CVE-2026-112936: filelock ReadWriteLock symlink following vulnerability

CVE-2026-112936 · Severity: medium · CVSS 6.1 · Published 2026-10-20

filelock is a Python library that provides platform-independent file locking. Versions 3.20.4 through 4.0.8 follow symbolic links in the database path, allowing a local attacker with write access to the lock directory to redirect lock operations to arbitrary files or create new files outside the intended location. This can break mutual exclusion between concurrent processes or cause unauthorized file creation and manipulation.

Technologies: filelock (PyPI), Tox-Dev Filelock. Vendors: PyPI, Tox-Dev.

Quick answers

Is CVE-2026-112936 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-112936 being exploited in the wild.
How severe is CVE-2026-112936?
Medium severity, with a CVSS score of 6.1, published 20 October 2026.
Which products and versions are affected?
filelock (PyPI) >= 3.20.4, <= 4.0.8, ECOSYSTEM:introduced=3.20.4,fixed=4.0.9; Tox-Dev Filelock 3.20.4 through 4.0.8.
Is there a fix for CVE-2026-112936?
Yes. filelock (PyPI): upgrade to 4.0.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-112936 attacked?
It is attacked with local access.
Am I affected by CVE-2026-112936?
Check whether you run filelock (PyPI) or Tox-Dev Filelock at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • filelock (PyPI): upgrade to 4.0.9 or later
    pip install "filelock>=4.0.9"

Technical details

ReadWriteLock and AsyncReadWriteLock resolve the lock database path using Path.resolve() and pass it directly to SQLite without rejecting symbolic links at the final path component. An attacker with local write access to the shared lock directory can plant a symlink that points to an alternate file, causing the victim process to open, lock, or create the symlink target, or to redirect between multiple targets across multiple lock attempts. The fix (version 4.0.9+) validates that the database path is a regular file using O_NOFOLLOW on POSIX systems and appropriate handle checks on Windows.

Affected products

  • tox-dev filelock 3.20.4 through 4.0.8

Identifiers

  • CVE-2026-112936
  • GHSA-j8f7-rjxc-mr56

Timeline

  • 2026-10-20: disclosed
  • 2026-10-01: patched

References

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