From 0c8828c60fb8b7087ecb0a5b1dafdc7f20c9d4a7 Mon Sep 17 00:00:00 2001 From: Christian Heimes Date: Tue, 11 Sep 2018 18:40:55 -0700 Subject: [PATCH] bpo-17239: Disable external entities in SAX parser The xml.sax and xml.dom.minidom parsers no longer processes external entities to increase security. Before, the parser created network connections to fetch remote files or loaded local files from the file system for DTD and entities. Signed-off-by: Christian Heimes --- Doc/library/xml.dom.pulldom.rst | 14 +++++ Doc/library/xml.rst | 6 +- Doc/library/xml.sax.rst | 8 +++ Doc/whatsnew/3.8.rst | 12 ++++ Lib/test/test_pulldom.py | 7 +++ Lib/test/test_sax.py | 60 ++++++++++++++++++- Lib/test/test_xml_etree.py | 13 ++++ Lib/xml/sax/expatreader.py | 2 +- .../2018-09-11-18-30-55.bpo-17239.kOpwK2.rst | 3 + 9 files changed, 120 insertions(+), 5 deletions(-) create mode 100644 Misc/NEWS.d/next/Security/2018-09-11-18-30-55.bpo-17239.kOpwK2.rst diff --git a/Doc/library/xml.dom.pulldom.rst b/Doc/library/xml.dom.pulldom.rst index 56f545c0e6d83e..eb2b16bd6c0b0c 100644 --- a/Doc/library/xml.dom.pulldom.rst +++ b/Doc/library/xml.dom.pulldom.rst @@ -25,6 +25,20 @@ events until either processing is finished or an error condition occurs. maliciously constructed data. If you need to parse untrusted or unauthenticated data see :ref:`xml-vulnerabilities`. +.. versionchanged:: 3.8 + + The SAX parser no longer processes general external entities by default to + increase security by default. To enable processing of external entities, + pass a custom parser instance in:: + + from xml.dom.pulldom import parse + from xml.sax import make_parser + from xml.sax.handler import feature_external_ges + + parser = make_parser() + parser.setFeature(feature_external_ges, True) + parse(filename, parser=parser) + Example:: diff --git a/Doc/library/xml.rst b/Doc/library/xml.rst index 63c24f80ac87c4..9b8ba6b17c8531 100644 --- a/Doc/library/xml.rst +++ b/Doc/library/xml.rst @@ -65,8 +65,8 @@ kind sax etree minidom p ========================= ============== =============== ============== ============== ============== billion laughs **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable** quadratic blowup **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable** -external entity expansion **Vulnerable** Safe (1) Safe (2) **Vulnerable** Safe (3) -`DTD`_ retrieval **Vulnerable** Safe Safe **Vulnerable** Safe +external entity expansion Safe (4) Safe (1) Safe (2) Safe (4) Safe (3) +`DTD`_ retrieval Safe (4) Safe Safe Safe (4) Safe decompression bomb Safe Safe Safe Safe **Vulnerable** ========================= ============== =============== ============== ============== ============== @@ -75,6 +75,8 @@ decompression bomb Safe Safe Safe S 2. :mod:`xml.dom.minidom` doesn't expand external entities and simply returns the unexpanded entity verbatim. 3. :mod:`xmlrpclib` doesn't expand external entities and omits them. +4. Since Python 3.8.0, external general entities are no longer processed by + default since Python. billion laughs / exponential entity expansion diff --git a/Doc/library/xml.sax.rst b/Doc/library/xml.sax.rst index 78d6633e098ba5..aa3ea9bfc55a98 100644 --- a/Doc/library/xml.sax.rst +++ b/Doc/library/xml.sax.rst @@ -24,6 +24,14 @@ the SAX API. constructed data. If you need to parse untrusted or unauthenticated data see :ref:`xml-vulnerabilities`. +.. versionchanged:: 3.8 + + The SAX parser no longer processes general external entities by default + to increase security. Before, the parser created network connections + to fetch remote files or loaded local files from the file + system for DTD and entities. The feature can be enabled again with method + :meth:`~xml.sax.xmlreader.XMLReader.setFeature` on the parser object + and argument :data:`~xml.sax.handler.feature_external_ges`. The convenience functions are: diff --git a/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst index 9aaaa761cc8a5c..e37a70f32d9952 100644 --- a/Doc/whatsnew/3.8.rst +++ b/Doc/whatsnew/3.8.rst @@ -155,6 +155,15 @@ venv activating virtual environments under PowerShell Core 6.1. (Contributed by Brett Cannon in :issue:`32718`.) +xml +--- + +* As mitigation against DTD and external entity retrieval, the + :mod:`xml.dom.minidom` and mod:`xml.sax` modules no longer process + external entities by default. + (Contributed by Christian Heimes in :issue:`17239`.) + + Optimizations ============= @@ -333,6 +342,9 @@ Changes in the Python API * :class:`uuid.UUID` now uses ``__slots__``, therefore instances can no longer be weak-referenced and attributes can no longer be added. +* :mod:`xml.dom.minidom` and mod:`xml.sax` modules no longer process + external entities by default. + (Contributed by Christian Heimes in :issue:`17239`.) CPython bytecode changes ------------------------ diff --git a/Lib/test/test_pulldom.py b/Lib/test/test_pulldom.py index f454098c65b1e9..4a1bad3442b25b 100644 --- a/Lib/test/test_pulldom.py +++ b/Lib/test/test_pulldom.py @@ -3,6 +3,7 @@ import xml.sax from xml.sax.xmlreader import AttributesImpl +from xml.sax.handler import feature_external_ges from xml.dom import pulldom from test.support import findfile @@ -166,6 +167,12 @@ def test_getitem_deprecation(self): # This should have returned 'END_ELEMENT'. self.assertEqual(parser[-1][0], pulldom.START_DOCUMENT) + def test_external_ges_default(self): + parser = pulldom.parseString(SMALL_SAMPLE) + saxparser = parser.parser + ges = saxparser.getFeature(feature_external_ges) + self.assertEqual(ges, False) + class ThoroughTestCase(unittest.TestCase): """Test the hard-to-reach parts of pulldom.""" diff --git a/Lib/test/test_sax.py b/Lib/test/test_sax.py index 2eb62905ffa882..3044960a0ed165 100644 --- a/Lib/test/test_sax.py +++ b/Lib/test/test_sax.py @@ -13,13 +13,14 @@ from xml.sax.saxutils import XMLGenerator, escape, unescape, quoteattr, \ XMLFilterBase, prepare_input_source from xml.sax.expatreader import create_parser -from xml.sax.handler import feature_namespaces +from xml.sax.handler import feature_namespaces, feature_external_ges from xml.sax.xmlreader import InputSource, AttributesImpl, AttributesNSImpl from io import BytesIO, StringIO import codecs import gc import os.path import shutil +from urllib.error import URLError from test import support from test.support import findfile, run_unittest, TESTFN @@ -911,6 +912,18 @@ def notationDecl(self, name, publicId, systemId): def unparsedEntityDecl(self, name, publicId, systemId, ndata): self._entities.append((name, publicId, systemId, ndata)) + + class TestEntityRecorder: + def __init__(self): + self.entities = [] + + def resolveEntity(self, publicId, systemId): + self.entities.append((publicId, systemId)) + source = InputSource() + source.setPublicId(publicId) + source.setSystemId(systemId) + return source + def test_expat_dtdhandler(self): parser = create_parser() handler = self.TestDTDHandler() @@ -927,6 +940,32 @@ def test_expat_dtdhandler(self): [("GIF", "-//CompuServe//NOTATION Graphics Interchange Format 89a//EN", None)]) self.assertEqual(handler._entities, [("img", None, "expat.gif", "GIF")]) + def test_expat_external_dtd_enabled(self): + parser = create_parser() + parser.setFeature(feature_external_ges, True) + resolver = self.TestEntityRecorder() + parser.setEntityResolver(resolver) + + with self.assertRaises(URLError): + parser.feed( + '\n' + ) + self.assertEqual( + resolver.entities, [(None, 'unsupported://non-existing')] + ) + + def test_expat_external_dtd_default(self): + parser = create_parser() + resolver = self.TestEntityRecorder() + parser.setEntityResolver(resolver) + + parser.feed( + '\n' + ) + parser.feed('') + parser.close() + self.assertEqual(resolver.entities, []) + # ===== EntityResolver support class TestEntityResolver: @@ -936,8 +975,9 @@ def resolveEntity(self, publicId, systemId): inpsrc.setByteStream(BytesIO(b"")) return inpsrc - def test_expat_entityresolver(self): + def test_expat_entityresolver_enabled(self): parser = create_parser() + parser.setFeature(feature_external_ges, True) parser.setEntityResolver(self.TestEntityResolver()) result = BytesIO() parser.setContentHandler(XMLGenerator(result)) @@ -951,6 +991,22 @@ def test_expat_entityresolver(self): self.assertEqual(result.getvalue(), start + b"") + def test_expat_entityresolver_default(self): + parser = create_parser() + self.assertEqual(parser.getFeature(feature_external_ges), False) + parser.setEntityResolver(self.TestEntityResolver()) + result = BytesIO() + parser.setContentHandler(XMLGenerator(result)) + + parser.feed('\n') + parser.feed(']>\n') + parser.feed('&test;') + parser.close() + + self.assertEqual(result.getvalue(), start + + b"") + # ===== Attributes support class AttrGatherer(ContentHandler): diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py index a52529051bf0d8..ecb910f04f5927 100644 --- a/Lib/test/test_xml_etree.py +++ b/Lib/test/test_xml_etree.py @@ -91,6 +91,12 @@ &entity; """ +EXTERNAL_ENTITY_XML = """\ + +]> +&entity; +""" def checkwarnings(*filters, quiet=False): def decorator(test): @@ -861,6 +867,13 @@ def test_entity(self): root = parser.close() self.serialize_check(root, 'text') + # 4) external (SYSTEM) entity + + with self.assertRaises(ET.ParseError) as cm: + ET.XML(EXTERNAL_ENTITY_XML) + self.assertEqual(str(cm.exception), + 'undefined entity &entity;: line 4, column 10') + def test_namespace(self): # Test namespace issues. diff --git a/Lib/xml/sax/expatreader.py b/Lib/xml/sax/expatreader.py index 421358fa5bc7f0..5066ffc2fa51f0 100644 --- a/Lib/xml/sax/expatreader.py +++ b/Lib/xml/sax/expatreader.py @@ -95,7 +95,7 @@ def __init__(self, namespaceHandling=0, bufsize=2**16-20): self._lex_handler_prop = None self._parsing = 0 self._entity_stack = [] - self._external_ges = 1 + self._external_ges = 0 self._interning = None # XMLReader methods diff --git a/Misc/NEWS.d/next/Security/2018-09-11-18-30-55.bpo-17239.kOpwK2.rst b/Misc/NEWS.d/next/Security/2018-09-11-18-30-55.bpo-17239.kOpwK2.rst new file mode 100644 index 00000000000000..8dd0fe8c1b533e --- /dev/null +++ b/Misc/NEWS.d/next/Security/2018-09-11-18-30-55.bpo-17239.kOpwK2.rst @@ -0,0 +1,3 @@ +The xml.sax and xml.dom.minidom parsers no longer processes external +entities by default. External DTD and ENTITY declarations no longer +load files or create network connections.