# CVE-2026-112908: filelock: StrictSoftFileLock creates its claim directories without the lock mode, so another local user with a write bit on them can end a live hold

Status: published. Published: 2026-11-05. Updated: 2026-11-05.

filelock is a platform-independent file lock for Python. From version 3.30.0 until version 4.2.1,  StrictSoftFileLock  and  AsyncStrictSoftFileLock  on POSIX systems create coordination and claim directories without applying the caller’s restrictive lock mode. A permissive umask or inherited default ACL can leave these directories writable by another local user, allowing that user to delete an active holder’s claims. Another authorized process can then acquire the lock while the original holder remains in its critical section. An attacker can also plant malformed claims to prevent acquisition. This issue is fixed in version 4.2.1.

## Remediation

- fix: filelock (PyPI): OSV reports a fixed version 4.2.1. Check the advisory for supported release branches. (source: OSV GHSA-6627-m3xw-93mp) — https://github.com/advisories/GHSA-6627-m3xw-93mp

## Affected products and versions

- tox-dev / filelock: >= 3.30.0, < 4.2.1 (affected). Source: CNA: GitHub_M
-  / filelock (filelock): 3.30.0 (affected, PyPI); 3.30.1 (affected, PyPI); 3.30.2 (affected, PyPI); 3.30.3 (affected, PyPI); 3.31.0 (affected, PyPI); 3.31.1 (affected, PyPI); 3.31.2 (affected, PyPI); 3.32.0 (affected, PyPI); 3.32.2 (affected, PyPI); 3.32.3 (affected, PyPI); 3.32.4 (affected, PyPI); 3.32.5 (affected, PyPI); 3.32.6 (affected, PyPI); 3.32.7 (affected, PyPI); 4.0.0 (affected, PyPI); 4.0.1 (affected, PyPI); 4.0.10 (affected, PyPI); 4.0.11 (affected, PyPI); 4.0.12 (affected, PyPI); 4.0.2 (affected, PyPI); 4.0.3 (affected, PyPI); 4.0.4 (affected, PyPI); 4.0.5 (affected, PyPI); 4.0.6 (affected, PyPI); 4.0.7 (affected, PyPI); 4.0.8 (affected, PyPI); 4.0.9 (affected, PyPI); 4.1.0 (affected, PyPI); 4.1.1 (affected, PyPI); 4.1.2 (affected, PyPI); 4.2.0 (affected, PyPI); Ecosystem version events: introduced 3.30.0; fixed 4.2.1. Source: OSV GHSA-6627-m3xw-93mp

## Severity and prioritization

- CVSS 3.1: 5.3 (medium); CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-732

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/tox-dev/filelock/security/advisories/GHSA-6627-m3xw-93mp (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/tox-dev/filelock/pull/839 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/tox-dev/filelock/commit/8cf51802158b9cf7e1fc560c2da30491a662cfde (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/tox-dev/filelock/releases/tag/4.2.1 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/advisories/GHSA-6627-m3xw-93mp (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-6627-m3xw-93mp (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-112908; retrieved 2026-11-05; source updated 2026-11-05

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-6627-m3xw-93mp; retrieved 2026-11-05; source updated 2026-10-28

Revision: 53aaecd47d6f5fd55cb3b415278ecb2a0c3d62fb1f9cef0289e62d91eef2ee3e

Canonical: https://y2.dev/cve/CVE-2026-112908

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