Vulnerability · Published Nov 5, 2026 · Assigned by GitHub_M
CVE-2026-112938filelock: StrictSoftFileLock follows a symbolic link swapped in at <path>.filelock and creates claim files in a directory another local user chooses
Medium 5.8
In plain English
A medium-severity security flaw in filelock from tox-dev. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 1% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
filelock is a platform-independent file lock for Python. From 3.30.0 until 4.2.1, On POSIX platforms, StrictSoftFileLock and AsyncStrictSoftFileLock validate the coordination directory in _ensure_protocol_directory but later reach the claims directory through _open_directory by pathname, allowing a local account that can rename the coordination name to swap in a symbolic link between check and use during acquisition. That race can create and leave claim files in another writable directory or strand claims in a different strict lock so the second lock times out. Separately, the claims property and force_break follow a resting symbolic link without a race when the lock user inspects or recovers the lock. Claims inspection discloses a file name to the other account only if the resulting exception text or claim_name reaches that account through a shared log, CI output, or error report. A blind force_break recovery that removes live claims from another strict lock can allow two processes into that lock's critical section; this path reaches other strict locks, not arbitrary files. 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-2026-112938 |
| Debian:13 | python-filelock | no fix listed | DEBIAN-CVE-2026-112938 |
| Debian:14 | python-filelock | no fix listed | DEBIAN-CVE-2026-112938 |
| PyPI | filelock | 4.2.1 | GHSA-m462-7rxw-wvpg |
| Ubuntu:26.04:LTS | python-filelock | no fix listed | UBUNTU-CVE-2026-112938 |
| Ubuntu:26.10 | python-filelock | no fix listed | UBUNTU-CVE-2026-112938 |
Affected products (as reported)
Weakness: CWE-363 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
References
- https://github.com/tox-dev/filelock/security/advisories/GHSA-m462-7rxw-wvpg x_refsource_CONFIRM
- https://github.com/tox-dev/filelock/pull/839 x_refsource_MISC
- https://github.com/tox-dev/filelock/commit/aaa18595d29795fab599a69d6b184d9a505dab4b 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