From 17b1d5d4e36aa57a9b25a0e694affbd1ee637e45 Mon Sep 17 00:00:00 2001 From: Christian Heimes Date: Sun, 23 Sep 2018 09:50:25 +0200 Subject: [PATCH] bpo-17239: Disable external entities in SAX parser (GH-9217) 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. Signed-off-by: Christian Heimes https://bugs.python.org/issue17239 --- 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 56f545c0e6d..eb2b16bd6c0 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 63c24f80ac8..9b8ba6b17c8 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 78d6633e098..aa3ea9bfc55 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 9aaaa761cc8..e37a70f32d9 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 f454098c65b..4a1bad3442b 100644 --- a/Lib/test/test_pulldom.py +++ b/Lib/test/test_pulldom.py @@ -3,6 +3,7 @@ import unittest 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 @@ class PullDOMTestCase(unittest.TestCase): # 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 2eb62905ffa..3044960a0ed 100644 --- a/Lib/test/test_sax.py +++ b/Lib/test/test_sax.py @@ -13,13 +13,14 @@ except SAXReaderNotAvailable: 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 @@ class ExpatReaderTest(XmlTestBase): 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 @@ class ExpatReaderTest(XmlTestBase): [("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 @@ class ExpatReaderTest(XmlTestBase): 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 @@ class ExpatReaderTest(XmlTestBase): 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 a52529051bf..ecb910f04f5 100644 --- a/Lib/test/test_xml_etree.py +++ b/Lib/test/test_xml_etree.py @@ -91,6 +91,12 @@ ENTITY_XML = """\ &entity; """ +EXTERNAL_ENTITY_XML = """\ + +]> +&entity; +""" def checkwarnings(*filters, quiet=False): def decorator(test): @@ -861,6 +867,13 @@ class ElementTreeTest(unittest.TestCase): 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 421358fa5bc..5066ffc2fa5 100644 --- a/Lib/xml/sax/expatreader.py +++ b/Lib/xml/sax/expatreader.py @@ -95,7 +95,7 @@ class ExpatParser(xmlreader.IncrementalParser, xmlreader.Locator): 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 00000000000..8dd0fe8c1b5 --- /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.