filelock: WindowsFileLock ignores mode: a 0o600 lock file and the ReadWriteLock database inherit the directory ACL

Exploitation

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

CVSS

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

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

filelock on Windows ignores the `mode` argument. `FileLock(path, mode=0o600)` creates the same file as `FileLock(path)`: one with no security descriptor of its own (the Windows record that says who may access a file). Its access list, or ACL, is whatever the lock directory hands down to new files. filelock creates the `ReadWriteLock` database, which it asks to be `0o600`, the same way. In a directory whose inheritable ACL grants other local accounts access to new files, those accounts can open the lock file or database. They can take the byte-range lock (a lock on a span of bytes in a file) once the owner releases it and keep the owner's later `acquire()` calls waiting or timing out. They can read holder metadata an `on_acquired` hook left in a `preserve_lock_file=True` file. Where the directory hands down modify access, they can write to both files. `lock.mode` still reports `0o600`. The documentation neither promises an ACL on Windows nor says that Windows drops the mode. On Unix…

Published by the source

28 Oct 2026, 21:08 UTC

Last modified by the source

28 Oct 2026, 21:15 UTC

Source last checked

29 Oct 2026, 06:10 UTC

1. Revision 2 · amended · 29 Oct 2026

   Amended from osv record GHSA-8mx5-7m5m-r77g

2. Revision 1 · created · 28 Oct 2026

   Published from ghsa record GHSA-8mx5-7m5m-r77g

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# Patch Next advisory brief: CVE-2026-112910

Advisory: filelock: WindowsFileLock ignores mode: a 0o600 lock file and the ReadWriteLock database inherit the directory ACL
IDs: CVE-2026-112910, GHSA-8mx5-7m5m-r77g
Record: https://patchnext.com/advisories/cve-2026-112910 (revision 2, source checked 29 Oct 2026, 06:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
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 >= 3.10.0, < 4.2.1; 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-8mx5-7m5m-r77g (GitHub-reviewed advisory GHSA-8mx5-7m5m-r77g lists affected ranges: PyPI filelock >=3.10.0 <=4.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-8mx5-7m5m-r77g (OSV record GHSA-8mx5-7m5m-r77g lists affected ranges: PyPI filelock >=3.10.0 <4.2.1 (fixed))

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