---
id: CVE-2025-0243
title: >-
  Memory safety bugs present in Firefox 133, Thunderbird 133, Firefox ESR 128.5,
  and Thunderbird 128.5
summary: >-
  Memory safety bugs present in Firefox 133, Thunderbird 133, Firefox ESR 128.5,
  and Thunderbird 128.5. Some of these bugs showed evidence of memory corruption
  and we presume that with enough effort some of these could have been exploited
  …
severity: medium
cvss: 5.1
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-787
vendor: mozilla
product: firefox
affected:
  - firefox < 128.6.0
  - firefox < 133.0
  - thunderbird < 128.6.0
  - 'thunderbird >= 129.0, < 134.0'
patched:
  - firefox 133.0
  - thunderbird 134.0
published: '2025-01-07'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T19:10:01.007'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-0243'
references:
  - url: 'https://bugzilla.mozilla.org/buglist.cgi?bug_id=1827142%2C1932783'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-01/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-02/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-04/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-05/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/01/msg00004.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.0025
epssPercentile: 0.14741
ingestedAt: '2026-09-30T19:21:07.219Z'
---

## Overview

Memory safety bugs present in Firefox 133, Thunderbird 133, Firefox ESR 128.5, and Thunderbird 128.5. 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 134, Firefox ESR 128.6, Thunderbird 134, and Thunderbird 128.6.

## Affected

- `firefox < 128.6.0`
- `firefox < 133.0`
- `thunderbird < 128.6.0`
- `thunderbird >= 129.0, < 134.0`

## Remediation

Upgrade past the affected range:

- `firefox 133.0`
- `thunderbird 134.0`