From 3d66a90357160e7122f318c657076fabeca982fa Mon Sep 17 00:00:00 2001
From: Petr Viktorin <encukou@gmail.com>
Date: Wed, 26 Aug 2026 11:29:07 +0200
Subject: [PATCH 1/3] Honor None result of filter for link fallbacks

---
 Lib/tarfile.py           |  4 +++-
 Lib/test/test_tarfile.py | 32 +++++++++++++++++++++++++++++---
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 6e092f1dcee5e88..a4f9ce3311f6dad 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -2841,9 +2841,11 @@ def makelink_with_filter(self, tarinfo, targetpath,
                     "makelink_with_filter: if filter_function is not None, "
                     + "extraction_root must also not be None")
             try:
-                filter_function(
+                filtered = filter_function(
                     unfiltered.replace(name=tarinfo.name, deep=False),
                     extraction_root)
+                if filtered is None:
+                    return
                 filtered = filter_function(unfiltered, extraction_root)
             except _FILTER_ERRORS as cause:
                 raise LinkFallbackError(tarinfo, unfiltered.name) from cause
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index be5abfe211fb929..61201ee0b8c7617 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -4621,9 +4621,15 @@ def test_sneaky_hardlink_fallback(self):
         for filter in 'tar', 'fully_trusted':
             with self.subTest(filter), self.check_context(arc.open(), filter):
                 if not os_helper.can_symlink():
-                    self.expect_file("a/t/dummy")
-                    self.expect_file("b/")
-                    self.expect_file("c/")
+                    if filter == 'tar':
+                        self.expect_exception(
+                            tarfile.LinkFallbackError,
+                            "link 'boom' would be extracted as a copy of "
+                            + "'c/escape', which was rejected")
+                    else:
+                        self.expect_file("a/t/dummy")
+                        self.expect_file("b/")
+                        self.expect_file("c/")
                 else:
                     self.expect_file("a/t/dummy")
                     self.expect_file("b/")
@@ -4820,6 +4826,26 @@ def testing_filter(member, path):
             if os_helper.can_chmod():
                 self.assertFalse(path.stat().st_mode & stat.S_IWUSR)
 
+    @symlink_test
+    def test_extract_filters_target_none(self):
+        # Test that when extract() falls back to extracting (rather than
+        # linking) a hardlink target, the member is rejected if the filter
+        # returns None.
+        with ArchiveMaker() as arc:
+            arc.add('a/b/s', symlink_to='../escape')
+            arc.add('q', hardlink_to='a/b/s')
+        def filter_unsafe_members(member, path):
+            try:
+                return tarfile.data_filter(member, path)
+            except tarfile.FilterError as error:
+                return None
+        tempdir = pathlib.Path(TEMPDIR) / 'extract'
+        with self.check_context(arc.open(), filter_unsafe_members):
+            if os_helper.can_symlink():
+                self.expect_file('a/b/s', symlink_to='../escape')
+            else:
+                self.expect_file('a/b/')  # symlink is not extracted
+
     def test_link_fallback_normalizes(self):
         # Make sure hardlink fallbacks work for non-normalized paths for all
         # filters

From 5c3e14662b21f7b9b30f435ee2922eb905b24ee0 Mon Sep 17 00:00:00 2001
From: Petr Viktorin <encukou@gmail.com>
Date: Thu, 10 Sep 2026 13:12:40 +0200
Subject: [PATCH 2/3] Apply review suggestions

Co-authored-by: Stan Ulbrych <stan@python.org>
---
 Lib/test/test_tarfile.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index 61201ee0b8c7617..598179983a7cbc5 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -4829,7 +4829,7 @@ def testing_filter(member, path):
     @symlink_test
     def test_extract_filters_target_none(self):
         # Test that when extract() falls back to extracting (rather than
-        # linking) a hardlink target, the member is rejected if the filter
+        # linking) a hardlink target, the member is skipped if the filter
         # returns None.
         with ArchiveMaker() as arc:
             arc.add('a/b/s', symlink_to='../escape')
@@ -4839,7 +4839,6 @@ def filter_unsafe_members(member, path):
                 return tarfile.data_filter(member, path)
             except tarfile.FilterError as error:
                 return None
-        tempdir = pathlib.Path(TEMPDIR) / 'extract'
         with self.check_context(arc.open(), filter_unsafe_members):
             if os_helper.can_symlink():
                 self.expect_file('a/b/s', symlink_to='../escape')

From aebd409a795adbee5b7daaf71d5af57cc1b7fd1f Mon Sep 17 00:00:00 2001
From: Petr Viktorin <encukou@gmail.com>
Date: Thu, 10 Sep 2026 13:38:41 +0200
Subject: [PATCH 3/3] Add NEWS file

---
 .../Security/2026-09-10-13-38-11.gh-issue-157265.-vYuMp.rst    | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Security/2026-09-10-13-38-11.gh-issue-157265.-vYuMp.rst

diff --git a/Misc/NEWS.d/next/Security/2026-09-10-13-38-11.gh-issue-157265.-vYuMp.rst b/Misc/NEWS.d/next/Security/2026-09-10-13-38-11.gh-issue-157265.-vYuMp.rst
new file mode 100644
index 000000000000000..ba27e47f734bfb1
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-09-10-13-38-11.gh-issue-157265.-vYuMp.rst
@@ -0,0 +1,3 @@
+In :mod:`tarfile`, when extracting a link falls back to extracting a member
+of the archive, skip the member when the filter function returns None when
+called with the extracted member's name replaced with the link's.