CVE-2026-11940tarfile extraction filter bypass allows escaping the destination directory

Official description

tarfile.extractall() with the 'data' or 'tar' filter could be bypassed by a crafted archive where a hardlink references a symlink stored at a deeper name than the hardlink itself.  The extraction fallback validated the symlink at it's archived location but recreated it at the hardlink's shallower path, letting a relative target the filter judged contained escape the destination directory.  This allowed a malicious tar archive to create a symlink pointing outside the destination, enabling out-of-destination file reads or writes. This was an incomplete fix of CVE-2025-4330.

Affected packages & fixed versions

Affected products (as reported)

References

• https://github.com/python/cpython/pull/151559 patch
• https://mail.python.org/archives/list/security-announce@python.org/thread/LD6QIISNQFQYOIEPJNEUIPV7S3V76FZH/ vendor-advisory
• https://github.com/python/cpython/issues/151558 issue-tracking
• https://github.com/python/cpython/commit/27dd970bf6b17ebca7c8ed486a40ab043ed7af8f patch
• https://github.com/python/cpython/commit/672825e2f36a57e173959b0d9d409d4560dab8df patch
• https://github.com/python/cpython/commit/771d12dda5140313db0ac550292987975651bbde patch
• https://github.com/python/cpython/commit/79c06bd5c6afa3c440d50faf7ee1b147c8832b4c patch
• https://github.com/python/cpython/commit/be13e86f6b9788a6f4d0419dffef72cbae5865c9 patch
• https://github.com/python/cpython/commit/e5fdbd8d5aa923bd9111b112ea73bd6ec7c47877 patch
• https://github.com/python/cpython/commit/0f852b3f07dd8e71e40326a51c02afbf16a42cc5 patch