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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
Mitigation details
CVE-2025-68146 NameCVE-2025-68146 Descriptionfilelock 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…
Workaround
s provide only partial mitigation. The race condition remains exploitable. Upgrading to version 3.20.1 is strongly recommended. SourceCVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more) Debian Bugs1123510 Vulnerable and fixed packages The table below lists information on source packages. Source PackageReleaseVersionStatus python-filelock (PTS)bullseye3.0.12-2vulnerable bookworm3.9.0-1vulnerable trixie3.18.0-1+deb13u1fixed forky, sid3.29.0-1fixed The information below is based on the following data on fixed versions. PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs python-filelocksourcetrixie3.18.0-1+deb13u1 python-filelocksource(unstable)3.20.2-11123510 Notes [bookworm] - python-filelock <no-dsa> (Minor issue) [bullseye] - python-filelock <postponed> (Minor issue) https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f https://github.com/tox-dev/filelock/pull/461 Fixed by: https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e (3.20.1)
CVE-2025-68146
| Name | 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. |
| Source | CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more) |
| Debian Bugs | 1123510 |
Vulnerable and fixed packages
The table below lists information on source packages.
| Source Package | Release | Version | Status |
|---|---|---|---|
| python-filelock (PTS) | bullseye | 3.0.12-2 | vulnerable |
| bookworm | 3.9.0-1 | vulnerable | |
| trixie | 3.18.0-1+deb13u1 | fixed | |
| forky, sid | 3.29.0-1 | fixed |
The information below is based on the following data on fixed versions.
| Package | Type | Release | Fixed Version | Urgency | Origin | Debian Bugs |
|---|---|---|---|---|---|---|
| python-filelock | source | trixie | 3.18.0-1+deb13u1 | |||
| python-filelock | source | (unstable) | 3.20.2-1 | 1123510 |
Notes
[bookworm] - python-filelock <no-dsa> (Minor issue)
[bullseye] - python-filelock <postponed> (Minor issue)
https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f
https://github.com/tox-dev/filelock/pull/461
Fixed by: https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e (3.20.1)
Apply commands
[bookworm] - python-filelock <no-dsa> (Minor issue)[bullseye] - python-filelock <postponed> (Minor issue)https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7fhttps://github.com/tox-dev/filelock/pull/461Fixed by: https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e (3.20.1)OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| sles | affected | | |
| debian | bookworm | affected | |
| debian | bullseye | affected | |
| debian | forky | fixed | 3.20.2-1 |
| debian | sid | fixed | 3.20.2-1 |
| debian | trixie | fixed | 3.18.0-1+deb13u1 |
Package impact
| Ecosystem | Package | Vulnerable | Fixed |
|---|---|---|---|
| PyPI | filelock | <3.20.1 | 3.20.1 |
References
- https://github.com/tox-dev/filelock/security/advisories/GHSA-w853-jp5j-5j7f
- https://github.com/tox-dev/filelock/commit/4724d7f8c3393ec1f048c93933e6e3e6ec321f0e
- https://github.com/tox-dev/filelock
- https://github.com/tox-dev/filelock/releases/tag/3.20.1
- https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants
- https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html
- https://www.suse.com/security/cve/CVE-2025-68146.html
- https://security-tracker.debian.org/tracker/CVE-2025-68146
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.