CVE-2026-112935: filelock — Exploit & Fix

Description

filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can break a stale marker after an attacker frees its own marker following the stale read, an honest contender creates a live successor on the reused inode, and the successor's modification time is not newer than the saved observation, causing the live marker to be removed and two holders to be admitted. This issue is fixed in version 4.2.1.

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CVSS v3.1 Score

4.7

MEDIUM

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

EPSS — Exploit Prediction

0.0013

Probability of exploitation

0.03%

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-367 CWE-367

Affected Products

Vendor	Product	Versions
tox-dev	filelock	3.22.0 — 4.2.1

References

Advisories & Patches

https://github.com/tox-dev/filelock/commit/740ff666b62a88496c8d7394e4e6230605e4d62b https://github.com/tox-dev/filelock/pull/843 https://github.com/tox-dev/filelock/security/advisories/GHSA-fq56-3cx3-fjxp

Exploits

https://github.com/tox-dev/filelock/security/advisories/GHSA-fq56-3cx3-fjxp

Other References

https://github.com/tox-dev/filelock/releases/tag/4.2.1

Frequently Asked Questions

What is CVE-2026-112935? +

filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can break a stale marker after an attacker frees its own marker following the stale read, an honest contender creates a live successor on the reused inode, and the successor's modification time is not newer than the saved observation, causing the live marker to be removed and two holders to be admitted. This issue is fixed in version 4.2.1. It has a CVSS v3.1 base score of 4.7 (MEDIUM).

How severe is CVE-2026-112935? +

CVE-2026-112935 has a CVSS v3.1 score of 4.7 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0013, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-112935? +

CVE-2026-112935 affects products from tox-dev, specifically: filelock. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-112935? +

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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