# filelock: StrictSoftFileLock follows a symbolic link swapped in at \<path>.filelock and creates claim files in a directory another local user chooses

Advisory record · `GHSA-m462-7rxw-wvpg`

- **Identifiers:** `GHSA-m462-7rxw-wvpg` · `CVE-2026-112938`
- **State:** Confirmed
- **Severity:** CVSS 5.8 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-363](https://cwe.mitre.org/data/definitions/363.html)
- **Tags:** [CWE-363](https://agentprime.io/advisories/tag/cwe-363.md)
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 28 Oct 2026, 21:08 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `filelock` (PyPI): affected `>=3.30.0, <4.2.1`; fixed in `4.2.1`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> filelock versions 3.30.0 through 4.2.0 are vulnerable in StrictSoftFileLock and AsyncStrictSoftFileLock, which can follow a symbolic link placed in the lock's coordination directory. A local user with an account who can rename that directory, which depends on the directory's permissions, can make the lock create claim files in a directory they choose, and this can block other processes from taking the lock. Upgrade to filelock 4.2.1, the fixed version. The source text is cut off in places.

Written 31 Oct 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.8 Medium, CVSS 3.1: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** No score.

## Timeline

- 31 Oct 2026, 14:07 UTC: First seen by agentprime
- 31 Oct 2026, 14:07 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-m462-7rxw-wvpg)
- 5 Nov 2026, 21:51 UTC: [Confirmed by the CVE List](https://www.cve.org/CVERecord?id=CVE-2026-112938)
- 5 Nov 2026, 22:17 UTC: [Confirmed by NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-112938)

## Sources

- [GitHub Advisory Database: GHSA-m462-7rxw-wvpg](https://github.com/advisories/GHSA-m462-7rxw-wvpg)
- [OSV: GHSA-m462-7rxw-wvpg](https://osv.dev/vulnerability/GHSA-m462-7rxw-wvpg)
- <https://github.com/tox-dev/filelock/security/advisories/GHSA-m462-7rxw-wvpg>
- <https://github.com/tox-dev/filelock/pull/839>
- <https://github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03>
- <https://github.com/tox-dev/filelock>
- <https://github.com/tox-dev/filelock/releases/tag/4.2.1>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-m462-7rxw-wvpg>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-m462-7rxw-wvpg/>. Everything for agents: <https://agentprime.io/llms.txt>.