CVE-2025-68146

Description

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.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
python-filelock	25.10 questing	Vulnerable
	25.04 plucky	Ignored end of life, was needs-triage
	24.04 LTS noble	Fixed 3.13.1-1ubuntu0.1~esm1
	22.04 LTS jammy	Fixed 3.6.0-1ubuntu0.1~esm1
	20.04 LTS focal	Fixed 3.0.12-2ubuntu0.1~esm1
	18.04 LTS bionic	Fixed 3.0.4-1ubuntu0.1~esm1

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Severity score breakdown

Parameter	Value
Base score	6.3 · Medium
Attack vector	Local
Attack complexity	High
Privileges required	Low
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	High
Availability impact	High
Vector	CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H

References

Related Ubuntu Security Notices (USN)

USN-7999-1
Filelock vulnerabilities
2 February 2026