CVE-2026-112911 filelock: StrictSoftFileLock and SoftReadWriteLock adopt a protocol directory another user created first, losing mutual exclusion

What is CVE-2026-112911?

CVE-2026-112911 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. From 3.30.0 until 4.2.1, StrictSoftFileLock versions from 3.30.0 and SoftReadWriteLock versions from 4.0.0 can adopt a protocol directory created first by another local user in a shared parent directory, allowing that user to alter protocol state and admit concurrent holders. This issue is fixed in version 4.2.1.

Weakness: CWE-283

Which versions are affected by CVE-2026-112911?

2 open source packages ship an affected version, including filelock. It affects 1 product.

Products include Tox-Dev Filelock.

How do I fix CVE-2026-112911?

Upgrade filelock to 4.2.1 or later.

Is CVE-2026-112911 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-112911 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 High 7.1
• CVE-2025-68146 filelock has TOCTOU race condition that allows symlink attacks during lock file creation Medium 6.3
• CVE-2026-112909 filelock: UnixFileLock truncates and chmods any regular file another user renames or hard-links onto the lock path Medium 6.1
• 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 Medium 6.1
• CVE-2026-112936 filelock: ReadWriteLock follows a symlink at the lock path into SQLite Medium 6.1

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2026-XZ00463, DEBIAN-CVE-2026-112911, GHSA-9c4x-gm8v-wgc4, UBUNTU-CVE-2026-112911.