---
id: CVE-2025-4091
title: >-
  Memory safety bugs present in Firefox 137, Thunderbird 137, Firefox ESR 128.9,
  and Thunderbird 128.9
summary: >-
  Memory safety bugs present in Firefox 137, Thunderbird 137, Firefox ESR 128.9,
  and Thunderbird 128.9. Some of these bugs showed evidence of memory corruption
  and we presume that with enough effort some of these could have been exploited
  …
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-119
vendor: mozilla
product: firefox
affected:
  - firefox < 128.10
  - firefox < 138.0
  - thunderbird < 128.10.0
  - thunderbird < 138.0
patched:
  - firefox 138.0
  - thunderbird 138.0
published: '2025-04-29'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-4091'
references:
  - url: 'https://bugzilla.mozilla.org/buglist.cgi?bug_id=1951161%2C1952105'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-28/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-29/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-31/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-32/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00498
epssPercentile: 0.40385
ingestedAt: '2026-09-30T18:17:24.436Z'
---

## Overview

Memory safety bugs present in Firefox 137, Thunderbird 137, Firefox ESR 128.9, and Thunderbird 128.9. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 138, Firefox ESR 128.10, Thunderbird 138, and Thunderbird 128.10.

## Affected

- `firefox < 128.10`
- `firefox < 138.0`
- `thunderbird < 128.10.0`
- `thunderbird < 138.0`

## Remediation

Upgrade past the affected range:

- `firefox 138.0`
- `thunderbird 138.0`