Vulnerability · Published Oct 20, 2026 · Assigned by GitHub_M

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

Medium 6.3

In plain English

A medium-severity security flaw in filelock from tox-dev. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 4% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.3Medium

Exploit odds (30 days)0.1%top 96.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	python-filelock	no fix listed	DEBIAN-CVE-2026-112911
Debian:13	python-filelock	no fix listed	DEBIAN-CVE-2026-112911
Debian:14	python-filelock	no fix listed	DEBIAN-CVE-2026-112911
PyPI	filelock	4.2.1	GHSA-9c4x-gm8v-wgc4
Ubuntu:26.04:LTS	python-filelock	no fix listed	UBUNTU-CVE-2026-112911
Ubuntu:26.10	python-filelock	no fix listed	UBUNTU-CVE-2026-112911

Affected products (as reported)

Vendor	Product	Versions
tox-dev	filelock	>= 3.30.0, < 4.2.1

Weakness: CWE-283 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H

References

https://github.com/tox-dev/filelock/security/advisories/GHSA-9c4x-gm8v-wgc4 x_refsource_CONFIRM
https://github.com/tox-dev/filelock/pull/839 x_refsource_MISC
https://github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03 x_refsource_MISC
https://github.com/tox-dev/filelock/releases/tag/4.2.1 x_refsource_MISC