What’s Vulnerable › Vulnerabilities

CVE-2026-112911: filelock: StrictSoftFileLock and SoftReadWriteLock adopt a protocol directory another user created first, losing mutual exclusion

• Severity: medium (CVSS 6.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-10-20 · updated 2026-10-28
• Weakness: CWE-283

Description

filelock is a platform-independent file lock for Python. From 3.30.0 until 4.2.1, StrictSoftFileLock versions from 3.30.0 and SoftReadWriteLock versions from 4.0.0 can adopt a protocol directory created first by another local user in a shared parent directory, allowing that user to alter protocol state and admit concurrent holders. This issue is fixed in version 4.2.1.

Affected products

• tox-dev filelock: from 3.30.0 before 4.2.1 — fixed in 4.2.1
• tox-dev filelock: from 3.30.0, < 4.2.1

How to fix

Upgrade to a fixed version: tox-dev filelock 4.2.1. Check the vendor advisory for mitigations.

References

• 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-9c4x-gm8v-wgc4
• https://github.com/tox-dev/filelock/security/advisories/GHSA-9c4x-gm8v-wgc4

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