Vulnerability · Published Oct 20, 2026 · Assigned by GitHub_M

CVE-2026-112909filelock: UnixFileLock truncates and chmods any regular file another user renames or hard-links onto the lock path

Medium 6.1

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 0.2% (higher than 13% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.1Medium

Exploit odds (30 days)0.2%top 87.3% 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. Prior to 4.2.1, UnixFileLock can truncate a regular file renamed onto the lock path when another local user has actual rename permission, or hard-linked there under a permissive hard-link policy; when an explicit mode is requested, affected versions from 3.10.2 can also change that file's mode. 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-2026-112909
Debian:13	python-filelock	no fix listed	DEBIAN-CVE-2026-112909
Debian:14	python-filelock	no fix listed	DEBIAN-CVE-2026-112909
PyPI	filelock	4.2.1	GHSA-69hj-f68j-2879
Ubuntu:26.04:LTS	python-filelock	no fix listed	UBUNTU-CVE-2026-112909
Ubuntu:26.10	python-filelock	no fix listed	UBUNTU-CVE-2026-112909

Affected products (as reported)

Vendor	Product	Versions
tox-dev	filelock	< 4.2.1

Weakness: CWE-706 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N

References

https://github.com/tox-dev/filelock/security/advisories/GHSA-69hj-f68j-2879 x_refsource_CONFIRM
https://github.com/tox-dev/filelock/pull/835 x_refsource_MISC
https://github.com/tox-dev/filelock/commit/e1e825b1992f69fb6b346dc395d5ae4893536c0a x_refsource_MISC
https://github.com/tox-dev/filelock/releases/tag/4.2.1 x_refsource_MISC