CVE-2026-112938

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CVE-2026-112938

Summary: filelock: StrictSoftFileLock follows a symbolic link swapped in at <path>.filelock and creates claim files in a directory another local user chooses

Details: 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.

References: https://github.com/tox-dev/filelock/releases/tag/4.2.1, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/112xxx/CVE-2026-112938.json, https://github.com/tox-dev/filelock/security/advisories/GHSA-m462-7rxw-wvpg, https://nvd.nist.gov/vuln/detail/CVE-2026-112938, https://github.com/tox-dev/filelock/commit/aaa18595d29795fab599a69d6b184d9a505dab4b, https://github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03, https://github.com/tox-dev/filelock/pull/839