---
id: CVE-2026-112911
title: >-
  filelock: StrictSoftFileLock and SoftReadWriteLock adopt a protocol directory
  another user created first, losing mutual exclusion
summary: >-
  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 s…
severity: medium
cvss: 6.3
cvssVector: 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-283
vendor: tox-dev
product: filelock
affected:
  - 'filelock >= 3.30.0, < 4.2.1'
published: '2026-10-20'
updated: '2026-10-20'
sourceUpdated: '2026-10-20T14:21:24.480Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-112911'
references:
  - url: >-
      https://github.com/tox-dev/filelock/security/advisories/GHSA-9c4x-gm8v-wgc4
    label: >-
      https://github.com/tox-dev/filelock/security/advisories/GHSA-9c4x-gm8v-wgc4
  - url: 'https://github.com/tox-dev/filelock/pull/839'
    label: 'https://github.com/tox-dev/filelock/pull/839'
  - url: >-
      https://github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03
    label: >-
      https://github.com/tox-dev/filelock/commit/bfa066d65a1ba9106f86ee9d027f7588b9c77e03
  - url: 'https://github.com/tox-dev/filelock/releases/tag/4.2.1'
    label: 'https://github.com/tox-dev/filelock/releases/tag/4.2.1'
tags:
  - cve.org
ingestedAt: '2026-10-20T15:09:24.127Z'
---

## Overview

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.

## Affected

- `filelock >= 3.30.0, < 4.2.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.