What’s Vulnerable › Vulnerabilities

CVE-2026-112939: filelock: SoftFileLock removes a live holder's marker when another user forges the PID in a writable marker

• Severity: medium (CVSS 4.7 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 2026-10-21
• Weakness: CWE-345

Description

filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can trust a forged process identifier in a marker that an attacker can modify but cannot remove, allowing an authorized contender such as another process of the holder's account or root to act as a confused deputy, remove the live marker, and admit another holder. This issue is fixed in version 4.2.1.

Affected products

• tox-dev filelock: from 3.22.0 before 4.2.1 — fixed in 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/eeceaa846cbe4df72718d94c8371ca1ab8f5b3cc
• https://github.com/tox-dev/filelock/pull/836
• https://github.com/tox-dev/filelock/releases/tag/4.2.1
• https://github.com/tox-dev/filelock/security/advisories/GHSA-rfpc-qcw5-3pc4
• https://github.com/tox-dev/filelock/security/advisories/GHSA-rfpc-qcw5-3pc4

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