filelock: SoftFileLock evicts a fresh lock file whose watched age another local user's pre-dated file passed on through inode reuse

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-112906: 0.17% estimated exploitation activity in the next 30 days; percentile 6.21 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

SoftFileLock and MarkerSoftFileLock evict an unparsable marker (the lock file at <path, whose presence says a process holds the lock) once a waiting contender has watched it unchanged for two seconds. SoftFileLease expires a lease the same way. The watch tells two looks apart by the marker's modification time (mtime) and inode number (the kernel's identity for a file, independent of its name) alone. Another local user (the other user below) who can create files in the lock's directory, a sticky /tmp included (the sticky bit is a directory flag that lets only a file's owner remove it), parks an empty file of its own at the lock path. It dates that file to a future tick of the kernel's coarse clock (a clock that advances in steps of 4 ms), lets the waiters of the user running the lock (the lock user below) watch it past two seconds, and unlinks it in that tick. On a filesystem that hands a freed inode number straight back (ext4, overlayfs on ext4) the lock user's next marker repeats…

Published by the source

23 Oct 2026, 22:00 UTC

Last modified by the source

23 Oct 2026, 22:15 UTC

Source last checked

26 Oct 2026, 13:55 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-2g95-wg33-c5x2

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-2g95-wg33-c5x2

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-2g95-wg33-c5x2

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# Patch Next advisory brief: CVE-2026-112906

Advisory: filelock: SoftFileLock evicts a fresh lock file whose watched age another local user's pre-dated file passed on through inode reuse
IDs: CVE-2026-112906, GHSA-2g95-wg33-c5x2
Record: https://patchnext.com/advisories/cve-2026-112906 (revision 3, source checked 26 Oct 2026, 13:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: filelock 4.2.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI filelock: affected >= 4.1.0, <= 4.2.0; fixed in 4.2.1

## Suggested inspection (read-only)
- `python -m pip show filelock`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on filelock.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-2g95-wg33-c5x2 (GitHub-reviewed advisory GHSA-2g95-wg33-c5x2 lists affected ranges: PyPI filelock >=4.1.0 <=4.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-2g95-wg33-c5x2 (OSV record GHSA-2g95-wg33-c5x2 lists affected ranges: PyPI filelock >=4.1.0 <4.2.1 (fixed))

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