Time-of-check Time-of-use (TOCTOU) Affecting python-filelock-doc package, versions <0:3.3.1-1.amzn2023.0.2


Severity

Recommended
0.0
medium
0
10

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.01% (1st percentile)

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  • Snyk IDSNYK-AMZN2023-PYTHONFILELOCKDOC-15246018
  • published6 Feb 2026
  • disclosed16 Dec 2025

Introduced: 16 Dec 2025

CVE-2025-68146  (opens in a new tab)
CWE-367  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 python-filelock-doc to version 0:3.3.1-1.amzn2023.0.2 or higher.
This issue was patched in ALAS2023-2026-1415.

NVD Description

Note: Versions mentioned in the description apply only to the upstream python-filelock-doc package and not the python-filelock-doc package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.

filelock is a platform-independent file lock for Python. In versions prior to 3.20.1, a Time-of-Check-Time-of-Use (TOCTOU) race condition allows local attackers to corrupt or truncate arbitrary user files through symlink attacks. The vulnerability exists in both Unix and Windows lock file creation where filelock checks if a file exists before opening it with O_TRUNC. An attacker can create a symlink pointing to a victim file in the time gap between the check and open, causing os.open() to follow the symlink and truncate the target file. All users of filelock on Unix, Linux, macOS, and Windows systems are impacted. The vulnerability cascades to dependent libraries. The attack requires local filesystem access and ability to create symlinks (standard user permissions on Unix; Developer Mode on Windows 10+). Exploitation succeeds within 1-3 attempts when lock file paths are predictable. The issue is fixed in version 3.20.1. If immediate upgrade is not possible, use SoftFileLock instead of UnixFileLock/WindowsFileLock (note: different locking semantics, may not be suitable for all use cases); ensure lock file directories have restrictive permissions (chmod 0700) to prevent untrusted users from creating symlinks; and/or monitor lock file directories for suspicious symlinks before running trusted applications. These workarounds provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended.

CVSS Base Scores

version 3.1