Time-of-check Time-of-use (TOCTOU) Race Condition Affecting filelock package, versions [3.22.0,4.2.1)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published20 Oct 2026
- disclosed20 Oct 2026
- creditAnthropic's OSS Scanner
Introduced: 20 Oct 2026
NewCVE-2026-112935 (opens in a new tab)How to fix?
Upgrade filelock to version 4.2.1 or higher.
Overview
Affected versions of this package are vulnerable to Time-of-check Time-of-use (TOCTOU) Race Condition via the stale-lock-breaking logic in _try_break_expired_lock and _try_break_stale_lock, where a race condition allows an attacker with write access to the lock directory to replace a held lock file with a new file between the time the inode is read and the time the break is executed. Because the original code did not pin the inode before acting on the stale marker, an attacker can cause the stale-break logic to evict a live lock, allowing two processes to hold the same lock simultaneously and corrupting the integrity guarantee that filelock provides.
Note: This is only exploitable when another local user has write access to the lock file's directory or any of its ancestor directories.