filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock

Exploitation

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

CVSS

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

EPSS

• CVE-2026-22701: 0.13% estimated exploitation activity in the next 30 days; percentile 2.34 (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.

Vulnerability Summary Title: Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock Affected Component: filelock package - SoftFileLock class File: src/filelock/soft.py lines 17-27 CWE: CWE-362, CWE-367, CWE-59 --- Description A TOCTOU race condition vulnerability exists in the SoftFileLock implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the acquire() method between raiseonnotwritablefile() (permission check) and os.open() (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. Attack Scenario --- Impact What kind of vulnerability is it? Who is impacted? This is a Time-of-Check-Time-of-Use…

Published by the source

13 Jan 2026, 18:44 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-qmgc-5h2g-mvrw

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-qmgc-5h2g-mvrw

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# Patch Next advisory brief: CVE-2026-22701

Advisory: filelock Time-of-Check-Time-of-Use (TOCTOU) Symlink Vulnerability in SoftFileLock
IDs: CVE-2026-22701, GHSA-qmgc-5h2g-mvrw
Record: https://patchnext.com/advisories/cve-2026-22701 (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 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: filelock 3.20.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI filelock: affected < 3.20.3; fixed in 3.20.3

## 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-qmgc-5h2g-mvrw (OSV record GHSA-qmgc-5h2g-mvrw lists affected ranges: PyPI filelock >=0 <3.20.3 (fixed))
- Verified: https://github.com/advisories/GHSA-qmgc-5h2g-mvrw (GitHub-reviewed advisory GHSA-qmgc-5h2g-mvrw lists affected ranges: PyPI filelock >=0 <3.20.3)

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