Time-of-check Time-of-use (TOCTOU) Race Condition Affecting filelock package, versions [4.1.0,4.2.1)
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-2026-112937 (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 ReadWriteLock cleanup logic in _read_write.py, which removes a randomized .filelock-* private hard-link directory during sweep operations. A local attacker with rename access in a non-sticky parent directory can observe a live link-directory name or forge a dead-owner sweep name, then rename a sibling directory onto it before the cleanup removes it, causing an arbitrary directory to be deleted. The link-directory name is derived from a digest that includes output from host_name(), which only adds a PID-namespace tag when /proc/self/ns/pid is readable, making the name predictable to any local user on macOS or systems without /proc.
Note: Exploitation requires either a macOS host or a Linux attacker that can enter a private mount namespace and mount an empty tmpfs over /proc, obscuring the PID-namespace tag.