filelock has a TOCTOU race condition which allows symlink attacks during lock file creation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.3 · CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H

EPSS

• CVE-2025-68146: 0.20% estimated exploitation activity in the next 30 days; percentile 9.57 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact A Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with OTRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. Who is impacted: All users of filelock on Unix, Linux, macOS, and Windows systems. The vulnerability cascades to dependent libraries: - virtualenv users: Configuration files can be overwritten with virtualenv metadata, leaking sensitive paths - PyTorch users: CPU ISA cache or model checkpoints can be corrupted, causing crashes or ML pipeline failures - poetry/tox users: through using virtualenv or filelock on their own. Attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix;…

Published by the source

16 Dec 2025, 20:52 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w853-jp5j-5j7f

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-w853-jp5j-5j7f

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2025-68146

Advisory: filelock has a TOCTOU race condition which allows symlink attacks during lock file creation
IDs: CVE-2025-68146, GHSA-w853-jp5j-5j7f
Record: https://patchnext.com/advisories/cve-2025-68146 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: filelock 3.20.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI filelock: affected < 3.20.1; fixed in 3.20.1

## Suggested inspection (read-only)
- `python -m pip show filelock`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on filelock.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-w853-jp5j-5j7f (OSV record GHSA-w853-jp5j-5j7f lists affected ranges: PyPI filelock >=0 <3.20.1 (fixed))
- Verified: https://github.com/advisories/GHSA-w853-jp5j-5j7f (GitHub-reviewed advisory GHSA-w853-jp5j-5j7f lists affected ranges: PyPI filelock >=0 <3.20.1)

Commands are suggestions: review each one before running it.