Vulnerability · Published Oct 20, 2026 · Assigned by GitHub_M
CVE-2026-112939filelock: SoftFileLock removes a live holder's marker when another user forges the PID in a writable marker
Medium 4.7
In plain English
A medium-severity insufficient verification of data authenticity 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 3% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
filelock is a platform-independent file lock for Python. From 3.22.0 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | python-filelock | no fix listed | DEBIAN-CVE-2026-112939 |
| Debian:13 | python-filelock | no fix listed | DEBIAN-CVE-2026-112939 |
| Debian:14 | python-filelock | no fix listed | DEBIAN-CVE-2026-112939 |
| PyPI | filelock | 4.2.1 | GHSA-rfpc-qcw5-3pc4 |
| Ubuntu:26.04:LTS | python-filelock | no fix listed | UBUNTU-CVE-2026-112939 |
| Ubuntu:26.10 | python-filelock | no fix listed | UBUNTU-CVE-2026-112939 |
Affected products (as reported)
Weakness: CWE-345 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N
References
- https://github.com/tox-dev/filelock/security/advisories/GHSA-rfpc-qcw5-3pc4 x_refsource_CONFIRM
- https://github.com/tox-dev/filelock/pull/836 x_refsource_MISC
- https://github.com/tox-dev/filelock/commit/eeceaa846cbe4df72718d94c8371ca1ab8f5b3cc x_refsource_MISC
- https://github.com/tox-dev/filelock/releases/tag/4.2.1 x_refsource_MISC