filelock: StrictSoftFileLock follows a symbolic link swapped in at <path>.filelock and creates claim files in a directory another local user chooses

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-112938
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-05 22:17:47 UTC
Updated2026-11-05 22:17:47 UTC
Descriptionfilelock is a platform-independent file lock for Python. From 3.30.0 until 4.2.1, On POSIX platforms, StrictSoftFileLock and AsyncStrictSoftFileLock validate the coordination directory in _ensure_protocol_directory but later reach the claims directory through _open_directory by pathname, allowing a local account that can rename the coordination name to swap in a symbolic link between check and use during acquisition. That race can create and leave claim files in another writable directory or strand claims in a different strict lock so the second lock times out. Separately, the claims property and force_break follow a resting symbolic link without a race when the lock user inspects or recovers the lock. Claims inspection discloses a file name to the other account only if the resulting exception text or claim_name reaches that account through a shared log, CI output, or error report. A blind force_break recovery that removes live claims from another strict lock can allow two processes into that lock's critical section; this path reaches other strict locks, not arbitrary files. This issue is fixed in version 4.2.1.

Risk And Classification

Primary CVSS: v3.1 5.8 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H

Problem Types: CWE-363 | CWE-363 CWE-363: Race Condition Enabling Link Following

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.8MEDIUMCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
3.1CNADECLARED5.8MEDIUMCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
High

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Tox-dev Filelock affected >= 3.30.0, < 4.2.1 Not specified

References

ReferenceSourceLinkTags
github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03 [email protected] github.com
github.com/tox-dev/filelock/releases/tag/4.2.1 [email protected] github.com
github.com/tox-dev/filelock/commit/aaa18595d29795fab599a69d6b184d9a505dab4b [email protected] github.com
github.com/tox-dev/filelock/pull/839 [email protected] github.com
github.com/tox-dev/filelock/security/advisories/GHSA-m462-7rxw-wvpg [email protected] github.com
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