From a235238fe0884e85cdacbc986a4749c5c4717212 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@python.org>
Date: Tue, 23 Jun 2026 14:31:38 +0100
Subject: [PATCH] gh-151558: Fix symlink escape via `tarfile`
 hardlink-extraction fallback (GH-151559)

---
 Lib/tarfile.py           |  3 +++
 Lib/test/test_tarfile.py | 23 +++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 3e03ebf..61d7e46 100755
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -2642,6 +2642,9 @@ class TarFile(object):
                     "makelink_with_filter: if filter_function is not None, "
                     + "extraction_root must also not be None")
             try:
+                filter_function(
+                    unfiltered.replace(name=tarinfo.name, deep=False),
+                    extraction_root)
                 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 0a7586a..d43559a 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -3543,6 +3543,29 @@ class TestExtractionFilters(unittest.TestCase):
                     self.expect_file("boom", symlink_to='../../link_here')
                     self.expect_file("c", symlink_to='b')
 
+    def test_sneaky_hardlink_fallback_deep(self):
+        # (CVE-2026-11940)
+        with ArchiveMaker() as arc:
+            arc.add("a/b/s", symlink_to=os.path.join("..", "escape"))
+            arc.add("s", hardlink_to=os.path.join("a", "b", "s"))
+
+        with self.check_context(arc.open(), 'data'):
+            e = self.expect_exception(
+                tarfile.LinkFallbackError,
+                "link 's' would be extracted as a copy of "
+                + "'a/b/s', which was rejected")
+            self.assertIsInstance(e.__cause__,
+                                  tarfile.LinkOutsideDestinationError)
+
+        for filter in 'tar', 'fully_trusted':
+            with self.subTest(filter), self.check_context(arc.open(), filter):
+                if not support.can_symlink():
+                    self.expect_file("a/")
+                    self.expect_file("a/b/")
+                else:
+                    self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
+                    self.expect_file("s", symlink_to=os.path.join('..', 'escape'))
+
     def test_exfiltration_via_symlink(self):
         # (CVE-2025-4138)
         # Test changing symlinks that result in a symlink pointing outside