---
id: CVE-2025-0247
title: Memory safety bugs present in Firefox 133 and Thunderbird 133
summary: >-
  Memory safety bugs present in Firefox 133 and Thunderbird 133. 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
  vulnerabili…
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-787
vendor: mozilla
product: firefox
affected:
  - firefox < 134.0
  - thunderbird < 134.0
patched:
  - firefox 134.0
  - 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-2025-0247'
references:
  - url: >-
      https://bugzilla.mozilla.org/buglist.cgi?bug_id=1835193%2C1910021%2C1919803%2C1931576%2C1931948%2C1932173
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-01/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-04/'
    label: security@mozilla.org
tags:
  - nvd
epss: 0.09273
epssPercentile: 0.95212
ingestedAt: '2026-09-30T19:21:07.221Z'
---

## Overview

Memory safety bugs present in Firefox 133 and Thunderbird 133. 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 and Thunderbird 134.

## Affected

- `firefox < 134.0`
- `thunderbird < 134.0`

## Remediation

Upgrade past the affected range:

- `firefox 134.0`
- `thunderbird 134.0`