lexicon · filelock: Symlink swap during SoftFileLock's writability check leaks whether a path exists and is writable by the lock
Affects lexiconSource GCVE Database
Not known to be exploited · CVSS 2.5 Low : upgrade to 3.25.2_5 when convenient.
Data as of 30 Oct 2026, 07:32 UTC
- Patch
- Available – fixed in 3.25.2_5
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:NExploitation evidence
Disclosed: evidence found.
CVE published 20 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
Upgrade lexicon to 3.25.2_5.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Homebrewlexiconpkg:brew/lexiconOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available in filelock version 3.25.2_5 that fixes this vulnerability. Users should upgrade to this version or later. On Linux systems, enabling the fs.protected_symlinks kernel setting (which is typically enabled by default) helps block this attack in sticky world-writable directories such as /tmp. Avoid using lock directories with 0777 permissions without the sticky bit or sticky group-writable directories to reduce exposure. No other specific mitigation is required as the vulnerability does not allow modification or denial of service.
Description
A symlink swap vulnerability in filelock's SoftFileLock writability check allows a local user to leak one bit of information about whether a path exists and is writable by the lock user. This occurs because the check uses os.lstat followed by os.access, which follows symlinks, enabling a time-of-check to time-of-use (TOCTOU) race condition. The vulnerability affects filelock versions 3.32.6 through 4.2.0 and is mitigated on Linux by the fs.protected_symlinks kernel setting in sticky world-writable directories like /tmp. The impact is limited to leaking a single bit of information per lock acquire attempt, with no integrity or availability impact. The vulnerability requires local access, the ability to create entries in the lock directory, and a race condition timing that is complex to achieve.
References
- github.com/tox-dev/filelock/security/advisories/GHSA-9j6q-wvj5-jgjg (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2026-112912 (opens in a new tab)
- github.com/tox-dev/filelock/pull/835 (opens in a new tab)
- github.com/tox-dev/filelock/commit/e1e825b1992f69fb6b346dc395d5ae4893536c0a (opens in a new tab)
- github.com/tox-dev/filelock (opens in a new tab)
- github.com/tox-dev/filelock/releases/tag/4.2.1 (opens in a new tab)