CVE-2025-68146
filelock has TOCTOU race condition that allows symlink attacks during lock file creation
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Timeline
ID reserved
By GitHub_M
- 1 day later
· 1 day later
Published
- 1 day later
· 1 day later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Medium6.3 | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H |
| NVDNVD · Analyzed | 3.1 | Medium6.5 | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H |
- EPSS (exploitation in 30 days)
- 0.20% · top 90% of all CVEs (7 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.3.
Weakness
- CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition (opens in a new tab)All about CWE-367 and its CVEs
- CWE-59: Improper Link Resolution Before File Access ('Link Following') (opens in a new tab)All about CWE-59 and its CVEs
- CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') (opens in a new tab)All about CWE-362 and its CVEs
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- PyPIfilelockGHSA-w853-jp5j-5j7f (opens in a new tab)
References (4)
- https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f (opens in a new tab)x_refsource_CONFIRM
- https://github.com/tox-dev/filelock/pull/461 (opens in a new tab)x_refsource_MISC
- https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e (opens in a new tab)x_refsource_MISC
- https://github.com/tox-dev/filelock/releases/tag/3.20.1 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-w853-jp5j-5j7f (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2025-68146)Record last updated .