# CVE-2026-112938: filelock: StrictSoftFileLock follows a symbolic link swapped in at <path>.filelock and creates claim files in a directory another local user chooses

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

filelock is a platform-independent file lock for Python. From 3.30.0 until 4.2.1, On POSIX platforms, StrictSoftFileLock and AsyncStrictSoftFileLock validate the coordination directory in _ensure_protocol_directory but later reach the claims directory through _open_directory by pathname, allowing a local account that can rename the coordination name to swap in a symbolic link between check and use during acquisition. That race can create and leave claim files in another writable directory or strand claims in a different strict lock so the second lock times out. Separately, the claims property and force_break follow a resting symbolic link without a race when the lock user inspects or recovers the lock. Claims inspection discloses a file name to the other account only if the resulting exception text or claim_name reaches that account through a shared log, CI output, or error report. A blind force_break recovery that removes live claims from another strict lock can allow two processes into that lock's critical section; this path reaches other strict locks, not arbitrary files. 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-m462-7rxw-wvpg) — https://github.com/advisories/GHSA-m462-7rxw-wvpg

## 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-m462-7rxw-wvpg

## Severity and prioritization

- CVSS 3.1: 5.8 (medium); CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-363

## 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-m462-7rxw-wvpg (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/aaa18595d29795fab599a69d6b184d9a505dab4b (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-m462-7rxw-wvpg (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-m462-7rxw-wvpg (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-112938; retrieved 2026-11-05; source updated 2026-11-05

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-m462-7rxw-wvpg; retrieved 2026-11-05; source updated 2026-10-28

Revision: cb530e37b4a8897fe88aed467acfe6b705028312f22d668ae8d24d6057dab820

Canonical: https://y2.dev/cve/CVE-2026-112938

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