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Vulnerabilities

Security fix · CVE-2026-112912

filelock is a platform-independent file lock for Python.

Published Oct 20, 2026 · catalog updated Oct 28, 2026 · filelock is a platform-independent

Last checked Nov 7, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-112912. EPSS is 0.21%. Act only if a listed version of filelock is a platform-independent is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (filelock is a platform-independent).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
Low2.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.21%
Remediation
Version ranges on file
Affected products
cpe tox-dev/filelock · pip filelock · pypi filelock

is the check that and the locks sharing its acquire path run before every attempt. It looks at the lock path with , so that it judges a planted symlink (a file that points at another path) by itself. When the node has no owner-write bit, it then calls , which follows symlinks. A local user who can create entries in the lock's directory can swap the path between a mode- file and a symlink to a path of their choosing. The second call then reports on the symlink's target with the permissions of the user running the lock (below: the lock user). The lock user's ends in within a fraction of a second when the target is missing or not writable by the lock user, and in the ordinary otherwise. That yields one bit per watched acquire. The bit says whether a path exists and is writable by the lock taker. It covers paths under directories the other user cannot search, or any path when root takes the lock. The lock does not open, create or modify anything through the symlink. On Linux, (a kernel setting that refuses to follow another user's symlink in a sticky world-writable directory) blocks it in a directory such as . It does not block it in a directory without the sticky bit (a directory flag that lets only a file's owner remove or rename it) or in a sticky group-writable one. This reopens the leak PR #567 closed. Affected versions are filelock 3.32.6 through 4.2.0. Anthropic's OSS Scanner reported this in private. Finding covered by this advisory: - [medium, CWE-59]: Symlink TOCTOU in raise_on_not_writable_file leaks file existence. ## Severity **CVSS 3.1 scores 2.5 (Low).** (local): the other user needs an account on the same host. (low privileges): an ordinary account is enough. (no user interaction). (high attack complexity): the swap has to land between two system calls a few bytecodes apart (6 to 12 % of back-to-back acquires with the other user on a second CPU, 1 in 8 000 on one CPU), and the other user has to observe how the lock user's acquire ended. (partial confiden

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe tox-dev/filelock< 4.2.1
  • pip filelock>= 3.32.6, <= 4.2.0
  • pypi filelockversion unspecified

How to fix CVE-2026-112912

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-112912. EPSS is 0.21%. Act only if a listed version of filelock is a platform-independent is installed.

Which versions are affected?

Compare what you have installed with < 4.2.1, >= 3.32.6, <= 4.2.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-59: Link Following. EPSS 0.21%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 20, 2026 · NIST NVD

    Detected

    filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory configuration that follows the link to infer whether a chosen path exists and is writable from the observable acquisition r

  2. Oct 20, 2026 · NIST NVD

    Updated

    filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory configuration that follows the link to infer whether a chosen path exists and is writable from the observable acquisition r

  3. Oct 20, 2026 · NIST NVD

    Updated

    filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory configuration that follows the link to infer whether a chosen path exists and is writable from the observable acquisition r

  4. Oct 21, 2026 · NIST NVD

    Updated

    filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory configuration that follows the link to infer whether a chosen path exists and is writable from the observable acquisition r

  5. Oct 28, 2026 · GitHub Advisory Database

    Updated

    is the check that and the locks sharing its acquire path run before every attempt. It looks at the lock path with , so that it judges a planted symlink (a file that points at another path) by itself. When the node has no owner-write bit, it then calls , which follows symlinks. A local user who can create entries in the lock's directory can swap the path between a mode- file and a symlink to a path

Sources

  • CVE.orgVulnerability recordCVE-2026-112912

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-112912

    30-day exploitation probability 0.21%

    first.org
  • GitHub Advisory DatabasePackage advisoryGHSA-9j6q-wvj5-jgjg

    filelock: Symlink swap during SoftFileLock's writability check leaks whether a path exists and is writable by the lock taker

    github.com
  • GitLab Advisory DatabasePackage advisoryCVE-2026-112912

    raise_on_not_writable_file() is the check that SoftFileLock and the locks sharing its acquire path run before every attempt. It looks at the lock path with os.lstat, so that it judges a planted symlink (a file that points at another path) by itself. When the node has no owner-write bit, it then calls os.access(filename, os.W_OK), which follows symlinks. A local user who can create entries in the l

    advisories.gitlab.com
  • NIST NVDVulnerability recordCVE-2026-112912

    filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory con

    nvd.nist.gov

References

Freshness

Last verified in this catalog Nov 7, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • GitLab Advisory DatabaseOct 30, 2026
  • GitHub Advisory DatabaseOct 29, 2026
  • FIRST EPSSOct 23, 2026
  • NIST NVDOct 22, 2026
  • CVE.orgOct 21, 2026