CVE-2026-112909 filelock: UnixFileLock truncates and chmods any regular file another user renames or hard-links onto the lock path
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-112909?
CVE-2026-112909 is a medium-severity vulnerability in tox-dev filelock, published on 20 Oct 2026.
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.
Weakness: CWE-706
Which versions are affected by CVE-2026-112909?
2 open source packages ship an affected version, including filelock. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
filelock PyPI | All versions | 4.2.1 |
filelock PyPI | All versions | 4.2.1 |
Products include Tox-Dev Filelock.
How do I fix CVE-2026-112909?
Upgrade filelock to 4.2.1 or later.
Is CVE-2026-112909 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-112909 exists.
Other vulnerabilities in tox-dev filelock
- CVE-2026-112940 filelock ReadWriteLock: SQLite reopens the lock database by name, so a planted symlink or journal file makes the lock user's process overwrite or unlink its own files
- CVE-2026-112911 filelock: StrictSoftFileLock and SoftReadWriteLock adopt a protocol directory another user created first, losing mutual exclusion
- CVE-2025-68146 filelock has TOCTOU race condition that allows symlink attacks during lock file creation
- CVE-2026-112934 filelock: SoftReadWriteLock holder refresh writes through a hard link and hangs on a named pipe that another local user renames over its record
- CVE-2026-112936 filelock: ReadWriteLock follows a symlink at the lock path into SQLite
Sources
Also known as AZL-110067, CLEANSTART-2026-ZN36596, DEBIAN-CVE-2026-112909, GHSA-69hj-f68j-2879, MINI-5vrg-6385-j6xg, MINI-vmj9-r77g-8m2h and 1 more.