[oss-security][CVE-2026-11940] Cpython: tarfile extraction filter bypass allows escaping the destination directory

[Alan Coopersmith <alan.coopersmith () oracle com>]

-------- Forwarded Message --------
Subject: 	[Security-announce][CVE-2026-11940] tarfile extraction filter bypass 
allows escaping the destination directory
Date:   Tue, 23 Jun 2026 16:55:19 +0100
From:   Stan Ulbrych via Security-announce <security-announce () python org>
Reply-To:       security-sig () python org
To:     security-announce () python org
CC:     Stan Ulbrych <stanulbrych () gmail com>



There is a HIGH severity vulnerability affecting CPython.

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.

Please see the linked CVE ID for the latest information on affected versions:

* https://www.cve.org/CVERecord?id=CVE-2026-11940
* https://github.com/python/cpython/pull/151559

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