From 65894cac0835cb8f469f649e20aa1be8bf89f5ae Mon Sep 17 00:00:00 2001
From: "Miss Skeleton (bot)" <31488909+miss-islington@users.noreply.github.com>
Date: Mon, 19 Oct 2020 19:35:23 -0700
Subject: bpo-42051: Reject XML entity declarations in plist files (GH-22760)

(cherry picked from commit 05ee790f4d1cd8725a90b54268fc1dfe5b4d1fa2)

Co-authored-by: Ronald Oussoren <ronaldoussoren@mac.com>
---
 Lib/plistlib.py                                        |  7 +++++++
 Lib/test/test_plistlib.py                              | 18 ++++++++++++++++++
 .../Security/2020-10-19-10-56-27.bpo-42051.EU_B7u.rst  |  3 +++
 3 files changed, 28 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Security/2020-10-19-10-56-27.bpo-42051.EU_B7u.rst

diff --git a/Lib/plistlib.py b/Lib/plistlib.py
index 04f8a87..533ed13 100644
--- a/Lib/plistlib.py
+++ b/Lib/plistlib.py
@@ -285,9 +285,16 @@ class _PlistParser:
         self.parser.StartElementHandler = self.handle_begin_element
         self.parser.EndElementHandler = self.handle_end_element
         self.parser.CharacterDataHandler = self.handle_data
+        self.parser.EntityDeclHandler = self.handle_entity_decl
         self.parser.ParseFile(fileobj)
         return self.root
 
+    def handle_entity_decl(self, entity_name, is_parameter_entity, value, base, system_id, public_id, notation_name):
+        # Reject plist files with entity declarations to avoid XML vulnerabilies in expat.
+        # Regular plist files don't contain those declerations, and Apple's plutil tool does not
+        # accept them either.
+        raise InvalidFileException("XML entity declarations are not supported in plist files")
+
     def handle_begin_element(self, element, attrs):
         self.data = []
         handler = getattr(self, "begin_" + element, None)
diff --git a/Lib/test/test_plistlib.py b/Lib/test/test_plistlib.py
index 0d887e2..de1c848 100644
--- a/Lib/test/test_plistlib.py
+++ b/Lib/test/test_plistlib.py
@@ -105,6 +105,19 @@ TESTDATA={
         AAABOQ=='''),
 }
 
+XML_PLIST_WITH_ENTITY=b'''\
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd" [
+   <!ENTITY entity "replacement text">
+  ]>
+<plist version="1.0">
+  <dict>
+    <key>A</key>
+    <string>&entity;</string>
+  </dict>
+</plist>
+'''
+
 
 class TestPlistlib(unittest.TestCase):
 
@@ -525,6 +538,11 @@ class TestPlistlib(unittest.TestCase):
         with self.assertRaises(OverflowError):
             plistlib.dumps(huge_uid, fmt=plistlib.FMT_BINARY)
 
+    def test_xml_plist_with_entity_decl(self):
+        with self.assertRaisesRegex(plistlib.InvalidFileException,
+                                    "XML entity declarations are not supported"):
+            plistlib.loads(XML_PLIST_WITH_ENTITY, fmt=plistlib.FMT_XML)
+
 
 class TestBinaryPlistlib(unittest.TestCase):
 
diff --git a/Misc/NEWS.d/next/Security/2020-10-19-10-56-27.bpo-42051.EU_B7u.rst b/Misc/NEWS.d/next/Security/2020-10-19-10-56-27.bpo-42051.EU_B7u.rst
new file mode 100644
index 0000000..e865ed1
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2020-10-19-10-56-27.bpo-42051.EU_B7u.rst
@@ -0,0 +1,3 @@
+The :mod:`plistlib` module no longer accepts entity declarations in XML
+plist files to avoid XML vulnerabilities. This should not affect users as
+entity declarations are not used in regular plist files.
-- 
cgit v0.12