From 91a9bd79cdbab8f8518c4a5e669b3f19680a2f31 Mon Sep 17 00:00:00 2001 From: Stan Ulbrych Date: Tue, 23 Jun 2026 14:31:38 +0100 Subject: [PATCH] gh-151558: Fix symlink escape via `tarfile` hardlink-extraction fallback (GH-151559) CVE: CVE-2026-11940 Upstream-Status: Backport [https://github.com/python/cpython/commit/27dd970bf6b17ebca7c8ed486a40ab043ed7af8f] Signed-off-by: Benjamin Robin --- Lib/tarfile.py | 3 +++ Lib/test/test_tarfile.py | 24 ++++++++++++++++++++++++ 2 files changed, 27 insertions(+) diff --git a/Lib/tarfile.py b/Lib/tarfile.py index 59d3f6e5cce1..83226e907e4b 100755 --- a/Lib/tarfile.py +++ b/Lib/tarfile.py @@ -2650,6 +2650,9 @@ def makelink_with_filter(self, tarinfo, targetpath, "makelink_with_filter: if filter_function is not None, " + "extraction_root must also not be None") try: + 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 759fa03ead70..29719d95b6c1 100644 --- a/Lib/test/test_tarfile.py +++ b/Lib/test/test_tarfile.py @@ -4080,6 +4080,30 @@ 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): + # (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 os_helper.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')) + @symlink_test def test_exfiltration_via_symlink(self): # (CVE-2025-4138) -- 2.54.0