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

Vulnerability summary

CVE-2026-11940 is a high (CVSS 7.8) vulnerability in python software foundation cpython. EPSS estimates a 0.75% chance of exploitation in the next 30 days, higher than 55% of scored vulnerabilities.

Timeline

1. 23-06-2026
   PublishedVulnerability first disclosed.
2. 13-08-2026
   Last modifiedVulnerability information updated.

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.

• CWE-22Improper Limitation of a Pathname to a Restricted DirectoryThe product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
• CWE-59Improper Link Resolution Before File AccessThe product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.