filelock: On Windows an oplock on a soft lock's marker holds SoftFileLock.acquire() past its timeout and blocks the stale break

Exploitation

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

CVSS

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

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

On Windows the soft locks (SoftFileLock, MarkerSoftFileLock, SoftFileLease, their async forms, and a FileLock that fell back to a soft lock) read their marker by path. The marker is the lock file whose presence says a process holds the lock. Each acquire() attempt that finds a marker opens it with os.open to read the holder's process id, and the lock renames and deletes a marker it judges stale, by path. On Windows each of these calls waits for an oplock. An oplock (opportunistic lock) is a request by a process that holds a handle on a file to be told before another process opens, renames or deletes that file; the other process waits until the holder answers the break or closes its handle. Another local account that can open the marker for reading can take a Level 1 oplock on it while no process holds it open, and leave the break unanswered. Every acquire() by the user running the lock (below: the lock user) then waits inside the open, past its timeout, blocking=False and…

Published by the source

23 Oct 2026, 22:27 UTC

Last modified by the source

23 Oct 2026, 22:45 UTC

Source last checked

26 Oct 2026, 13:56 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-567q-5qvw-pf92

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-567q-5qvw-pf92

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-567q-5qvw-pf92

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# Patch Next advisory brief: CVE-2026-112907

Advisory: filelock: On Windows an oplock on a soft lock's marker holds SoftFileLock.acquire() past its timeout and blocks the stale break
IDs: CVE-2026-112907, GHSA-567q-5qvw-pf92
Record: https://patchnext.com/advisories/cve-2026-112907 (revision 3, source checked 26 Oct 2026, 13:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.5)
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 >= 3.22.0, <= 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-567q-5qvw-pf92 (GitHub-reviewed advisory GHSA-567q-5qvw-pf92 lists affected ranges: PyPI filelock >=3.22.0 <=4.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-567q-5qvw-pf92 (OSV record GHSA-567q-5qvw-pf92 lists affected ranges: PyPI filelock >=3.22.0 <4.2.1 (fixed))

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