---
id: CVE-2026-112939
title: >-
  filelock: SoftFileLock removes a live holder's marker when another user forges
  the PID in a writable marker
summary: >-
  filelock is a platform-independent file lock for Python. From 3.22.0 until
  4.2.1, SoftFileLock can trust a forged process identifier in a marker that an
  attacker can modify but cannot remove, allowing an authorized contender such
  as anot…
severity: medium
cvss: 4.7
cvssVector: 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N'
cvssSource: cna
cwe:
  - CWE-345
vendor: tox-dev
product: filelock
affected:
  - 'filelock >= 3.22.0, < 4.2.1'
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-20T15:14:32.481979Z'
exploitAvailable: true
published: '2026-10-20'
updated: '2026-10-20'
sourceUpdated: '2026-10-20T15:14:56.836Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-112939'
references:
  - url: >-
      https://github.com/tox-dev/filelock/security/advisories/GHSA-rfpc-qcw5-3pc4
    label: >-
      https://github.com/tox-dev/filelock/security/advisories/GHSA-rfpc-qcw5-3pc4
  - url: 'https://github.com/tox-dev/filelock/pull/836'
    label: 'https://github.com/tox-dev/filelock/pull/836'
  - url: >-
      https://github.com/tox-dev/filelock/commit/eeceaa846cbe4df72718d94c8371ca1ab8f5b3cc
    label: >-
      https://github.com/tox-dev/filelock/commit/eeceaa846cbe4df72718d94c8371ca1ab8f5b3cc
  - 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
  - exploit-available
ingestedAt: '2026-10-20T15:09:24.119Z'
---

## Overview

filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can trust a forged process identifier in a marker that an attacker can modify but cannot remove, allowing an authorized contender such as another process of the holder's account or root to act as a confused deputy, remove the live marker, and admit another holder. This issue is fixed in version 4.2.1.

## Affected

- `filelock >= 3.22.0, < 4.2.1`

## Remediation

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