---
id: CVE-2025-6424
title: A use-after-free in FontFaceSet resulted in a potentially exploitable crash
summary: >-
  A use-after-free in FontFaceSet resulted in a potentially exploitable crash.
  This vulnerability was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR
  128.12, Thunderbird 140, and Thunderbird 128.12.
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
vendor: mozilla
product: firefox
affected:
  - firefox < 115.25.0
  - firefox < 140.0
  - 'firefox >= 116.0, < 128.12.0'
patched:
  - firefox 128.12.0
published: '2025-06-24'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6424'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1966423'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-51/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-52/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-53/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-54/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-55/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/06/msg00029.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.0439
epssPercentile: 0.90986
ingestedAt: '2026-09-30T18:17:24.442Z'
---

## Overview

A use-after-free in FontFaceSet resulted in a potentially exploitable crash. This vulnerability was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

## Affected

- `firefox < 115.25.0`
- `firefox < 140.0`
- `firefox >= 116.0, < 128.12.0`

## Remediation

Upgrade past the affected range:

- `firefox 128.12.0`