Fix bypass

Author: StanFromIreland

Lib/tarfile.py

@@ -2784,7 +2784,9 @@ def makelink_with_filter(self, tarinfo, targetpath,
                     "makelink_with_filter: if filter_function is not None, "
                     + "extraction_root must also not be None")
             try:
-                filtered = filter_function(unfiltered, extraction_root)
+                filtered = filter_function(
+                    unfiltered.replace(name=tarinfo.name, deep=False),
+                    extraction_root)
             except _FILTER_ERRORS as cause:
                 raise LinkFallbackError(tarinfo, unfiltered.name) from cause
         if filtered is not None:

Lib/test/test_tarfile.py

@@ -4413,6 +4413,33 @@ def test_sneaky_hardlink_fallback(self):
                     self.expect_file("boom", symlink_to='../../link_here')
                     self.expect_file("c", symlink_to='b')
 
+    @symlink_test
+    def test_sneaky_hardlink_fallback_deep(self):
+        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'):
+            if not os_helper.can_symlink() or sys.platform == "win32":
+                # See notes in test_sneaky_hardlink_fallback.
+                self.expect_exception(tarfile.LinkOutsideDestinationError)
+            else:
+                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 os_helper.can_symlink():
+                    self.expect_file("a/b/s")
+                    self.expect_file("s")
+                else:
+                    self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
+                    self.expect_file("s", symlink_to=os.path.join('..', 'escape'))
+
     @symlink_test
     def test_exfiltration_via_symlink(self):
         # (CVE-2025-4138)

Misc/NEWS.d/next/Security/2026-06-10-13-08-19.gh-issue-111111.mL74i2.rst

@@ -0,0 +1,3 @@
+Fixed an vulnerability in the :mod:`tarfile` ``data`` and ``tar`` extraction
+filters where crafted archives could create a symlink pointing outside the
+destination directory. This was a bypass of :cve:`2025-4330`.