gh-160097: Reject links replacing the destination in tarfile.tar_filter (#160098)

Author: StanFromIreland

Doc/library/tarfile.rst

@@ -1131,6 +1131,11 @@ reused in custom filters:
   - :ref:`Refuse <tarfile-extraction-refuse>` to extract files whose absolute
     path (after following symlinks) would end up outside the destination.
     This raises :class:`~tarfile.OutsideDestinationError`.
+  - :ref:`Refuse <tarfile-extraction-refuse>` to extract links (hard or soft)
+    whose name refers to the destination directory itself.
+    This raises :class:`~tarfile.OutsideDestinationError`.
+    Note that such files are refused even on platforms that do not support
+    symbolic links.
   - Clear high mode bits (setuid, setgid, sticky) and group/other write bits
     (:const:`~stat.S_IWGRP` | :const:`~stat.S_IWOTH`).
 

Lib/tarfile.py

@@ -854,6 +854,12 @@ def _get_filtered_attrs(member, dest_path, for_data=True):
                                    strict=os.path.ALLOW_MISSING)
     if os.path.commonpath([target_path, dest_path]) != dest_path:
         raise OutsideDestinationError(member, target_path)
+    # A link member named after the destination directory itself
+    # would replace it with a (sym)link, redirecting the destination
+    # for all subsequent members.
+    if ((member.islnk() or member.issym())
+            and os.path.normpath(name) == os.curdir):
+        raise OutsideDestinationError(member, target_path)
     # Limit permissions (no high bits, and go-w)
     mode = member.mode
     if mode is not None:
@@ -889,11 +895,6 @@ def _get_filtered_attrs(member, dest_path, for_data=True):
         if member.islnk() or member.issym():
             if os.path.isabs(member.linkname):
                 raise AbsoluteLinkError(member)
-            # A link member that resolves to the destination directory itself
-            # would replace it with a (sym)link, redirecting the destination
-            # for all subsequent members.
-            if target_path == dest_path:
-                raise OutsideDestinationError(member, target_path)
             normalized = os.path.normpath(member.linkname)
             if normalized != member.linkname:
                 new_attrs['linkname'] = normalized

Lib/test/test_tarfile.py

@@ -4671,8 +4671,10 @@ def test_link_at_destination(self):
                 t.linkname = '.'
                 arc.tar_w.addfile(t)
 
-            with self.check_context(arc.open(), 'data'):
-                self.expect_exception(tarfile.OutsideDestinationError)
+            for filter in 'tar', 'data':
+                with self.subTest(name=name, filter=filter):
+                    with self.check_context(arc.open(), filter):
+                        self.expect_exception(tarfile.OutsideDestinationError)
 
     @symlink_test
     @os_helper.skip_unless_symlink

Misc/NEWS.d/next/Security/2026-10-21-19-58-53.gh-issue-160097.-opfAL.rst

@@ -0,0 +1,5 @@
+.. cve: CVE-2026-114583
+
+:func:`tarfile.tar_filter` now rejects link members whose path resolves to
+the destination directory itself, as :func:`tarfile.data_filter` already
+did.