CVE-2026-112938 (CVSS 5.8)

Description

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.

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CVSS v3.1 Score

5.8

MEDIUM

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

EPSS — Exploit Prediction

0.0011

Probability of exploitation

0.01%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-363 CWE-363

References

Other References

https://github.com/tox-dev/filelock/commit/aaa18595d29795fab599a69d6b184d9a505dab4b https://github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03 https://github.com/tox-dev/filelock/pull/839 https://github.com/tox-dev/filelock/releases/tag/4.2.1 https://github.com/tox-dev/filelock/security/advisories/GHSA-m462-7rxw-wvpg

Frequently Asked Questions

What is CVE-2026-112938? +

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. It has a CVSS v3.1 base score of 5.8 (MEDIUM).

How severe is CVE-2026-112938? +

CVE-2026-112938 has a CVSS v3.1 score of 5.8 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0011, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-112938? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-112938