bpo-42051: Reject XML entity declarations in plist files (#22760)

1 files changed, 7 insertions, 0 deletions

diff --git a/Lib/plistlib.py b/Lib/plistlib.py
index aff5fe3..ba7ac19 100644
--- a/Lib/plistlib.py
+++ b/Lib/plistlib.py
@@ -173,9 +173,16 @@ 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)