filelock ReadWriteLock: a crafted lock database makes every acquire stall or hang regardless of timeout

Exploitation

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

CVSS

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

EPSS

• CVE-2026-112915: 0.22% estimated exploitation activity in the next 30 days; percentile 12.30 (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) run `PRAGMA journal_mode=MEMORY` on a fresh connection for every acquire. That statement makes SQLite load the whole schema (the `sqlite_master` table, which lists every table and index with its `CREATE` text) of whatever file sits at the lock path. The caller's `timeout` reaches SQLite only as `busy_timeout`, which bounds waits for another connection's lock, not schema loading. The only content checks reject non-regular files and WAL mode (write-ahead log, an SQLite mode that keeps changes in a side file). A local user who can place or overwrite the file at a `ReadWriteLock`'s database path can therefore make every `acquire_read` / `acquire_write` of every process using that lock ignore its `timeout` and `blocking=False`. That position needs a non-sticky shared directory, or a database owned by the user running the lock (below: the lock user) that other users may write. One 37 KB crafted file stalls each…

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, 06:25 UTC

1. Revision 2 · amended · 29 Oct 2026

   Amended from osv record GHSA-cwqr-hh33-gh44

2. Revision 1 · created · 28 Oct 2026

   Published from ghsa record GHSA-cwqr-hh33-gh44

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# Patch Next advisory brief: CVE-2026-112915

Advisory: filelock ReadWriteLock: a crafted lock database makes every acquire stall or hang regardless of timeout
IDs: CVE-2026-112915, GHSA-cwqr-hh33-gh44
Record: https://patchnext.com/advisories/cve-2026-112915 (revision 2, source checked 29 Oct 2026, 06:25 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
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 >= 3.20.4, < 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-cwqr-hh33-gh44 (GitHub-reviewed advisory GHSA-cwqr-hh33-gh44 lists affected ranges: PyPI filelock >=3.20.4 <=4.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-cwqr-hh33-gh44 (OSV record GHSA-cwqr-hh33-gh44 lists affected ranges: PyPI filelock >=3.20.4 <4.2.1 (fixed))

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