GHSA-rfpc-qcw5-3pc4: filelock (CVE-2026-112939)

Package	Ecosystem	Affected	Fixed in
filelock	PyPI	>=3.22.0, <4.2.1	4.2.1

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

GHSA-rfpc-qcw5-3pc4 affects the PyPI package filelock from 3.22.0 through 4.2.0, in its soft-lock classes (SoftFileLock, MarkerSoftFileLock, SoftFileLease, their async variants, and FileLock falling back to a soft lock on ENOSYS). A local user who can write the lock marker file but not remove it can rewrite the holder's record to name a dead process, so a contender running as the holder's account or root removes the live marker and acquires the lock, letting two processes run the critical section together. Upgrade to filelock 4.2.1, which is the fixed version listed.

Written 31 Oct 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
4.7	Medium	3.1	CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0014, the 3rd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:07 UTC First seen by agentprime
31 Oct 2026, 14:07 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.