Vulnerability · Published Oct 20, 2026 · Assigned by GitHub_M
CVE-2026-112912filelock: Symlink swap during SoftFileLock's writability check leaks whether a path exists and is writable by the lock taker
Low 2.5
In plain English
A low-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 12% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory configuration that follows the link to infer whether a chosen path exists and is writable from the observable acquisition result. 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-2026-112912 |
| Debian:13 | python-filelock | no fix listed | DEBIAN-CVE-2026-112912 |
| Debian:14 | python-filelock | no fix listed | DEBIAN-CVE-2026-112912 |
| PyPI | filelock | 4.2.1 | GHSA-9j6q-wvj5-jgjg |
| Ubuntu:26.04:LTS | python-filelock | no fix listed | UBUNTU-CVE-2026-112912 |
| Ubuntu:26.10 | python-filelock | no fix listed | UBUNTU-CVE-2026-112912 |
Affected products (as reported)
Weakness: CWE-59 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
References
- https://github.com/tox-dev/filelock/security/advisories/GHSA-9j6q-wvj5-jgjg 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