filelock ReadWriteLock: SQLite reopens the lock database by name, so a planted symlink or journal file makes the lock user's process overwrite or unlink its own files

Exploitation

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

CVSS

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

EPSS

• CVE-2026-112940: 0.19% estimated exploitation activity in the next 30 days; percentile 8.79 (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.

ReadWriteLock and AsyncReadWriteLock (the SQLite-backed reader/writer lock) hand SQLite a name they do not control. On Linux the lock validates its database through a descriptor (the number the kernel gives a process for an open file). It then connects SQLite to /proc/self/fd/<n, a Linux path that names the process's own open file n. SQLite turns that path back into a plain path and reopens it by name, following symlinks (a symlink is a file that points at another path). On every POSIX route SQLite also acts on -journal, -wal and -shm files it finds beside that name. Those are SQLite's side files: the rollback journal (pages saved to undo an interrupted write), the write-ahead log or WAL (changes kept outside the main file), and the shared-memory index for the WAL. Another local user who can create or rename entries in the directory that holds the lock database can turn this against the user running the lock (below: the lock user). Such a directory is a 0777 or group-writable cache,…

Published by the source

23 Oct 2026, 21:59 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-v4x8-3wr5-3wq8

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-v4x8-3wr5-3wq8

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-v4x8-3wr5-3wq8

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-112940

Advisory: filelock ReadWriteLock: SQLite reopens the lock database by name, so a planted symlink or journal file makes the lock user's process overwrite or unlink its own files
IDs: CVE-2026-112940, GHSA-v4x8-3wr5-3wq8
Record: https://patchnext.com/advisories/cve-2026-112940 (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: High (CVSS 7.1)
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 >= 3.20.4, <= 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-v4x8-3wr5-3wq8 (GitHub-reviewed advisory GHSA-v4x8-3wr5-3wq8 lists affected ranges: PyPI filelock >=3.20.4 <=4.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-v4x8-3wr5-3wq8 (OSV record GHSA-v4x8-3wr5-3wq8 lists affected ranges: PyPI filelock >=3.20.4 <4.2.1 (fixed))

Commands are suggestions: review each one before running it.