---
id: "CVE-2026-112911"
kind: "vulnerability"
aliases: ["CVE-2026-112911"]
title: "filelock: local users can break lock state in shared directories"
severity: "medium"
cvss: 6.3
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "tox-dev filelock", "fixed": ["4.2.1"], "affected": ">= 3.30.0, < 4.2.1", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["filelock", "multi-user-hosts", "package", "python", "shared-tmp"]
not_affected_if: ["other-lock-classes", "private-lock-directory", "single-user-host"]
published_at: "2026-10-20T15:17:15+00:00"
first_seen_at: "2026-10-23T21:57:20+00:00"
updated_at: "2026-10-25T04:01:36+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-112911", "first_seen_at": "2026-10-23T21:57:20+00:00"}]
---

# filelock: local users can break lock state in shared directories

filelock is a Python library for cross-process file locks. Between versions 3.30.0 and 4.2.1, StrictSoftFileLock and SoftReadWriteLock can adopt a lock directory created first by another local user in a shared parent directory, letting that user alter lock state and let concurrent holders in.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:tox-dev filelock affected >= 3.30.0, < 4.2.1 fixed 4.2.1

## How to check

- Run `pip show filelock` or `pip freeze | grep -i filelock` and check whether the version is at least `3.30.0` and below `4.2.1`.
- Check whether code uses `StrictSoftFileLock` or `SoftReadWriteLock` with lock paths in a shared directory such as `/tmp`.

## Fix

- Upgrade filelock to `4.2.1` or later.
- Until upgraded, keep lock paths in directories only the application user can write to.

## Timeline

- 2026-10-23T21:57:20+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-112911

## From the sources

filelock is a platform-independent file lock for Python. From 3.30.0 until 4.2.1, StrictSoftFileLock versions from 3.30.0 and SoftReadWriteLock versions from 4.0.0 can adopt a protocol directory created first by another local user in a shared parent directory, allowing that user to alter protocol state and admit concurrent holders. This issue is fixed in version 4.2.1.

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