---
id: CVE-2025-9181
title: Uninitialized memory in the JavaScript Engine component
summary: >-
  Uninitialized memory in the JavaScript Engine component. This vulnerability
  was fixed in Firefox 142, Firefox ESR 128.14, Firefox ESR 140.2, Thunderbird
  142, Thunderbird 128.14, and Thunderbird 140.2.
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N'
cwe:
  - CWE-457
vendor: mozilla
product: firefox
affected:
  - firefox < 128.14.0
  - firefox < 142.0
  - 'firefox >= 140.0, < 140.2.0'
  - thunderbird < 128.14.0
  - thunderbird < 142.0
  - 'thunderbird >= 140.0, < 140.2.0'
patched:
  - firefox 140.2.0
  - thunderbird 140.2.0
published: '2025-08-19'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-9181'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1977130'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-64/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-66/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-67/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-70/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-71/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-72/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/08/msg00016.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/08/msg00018.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00374
epssPercentile: 0.28884
ingestedAt: '2026-09-30T18:17:24.456Z'
---

## Overview

Uninitialized memory in the JavaScript Engine component. This vulnerability was fixed in Firefox 142, Firefox ESR 128.14, Firefox ESR 140.2, Thunderbird 142, Thunderbird 128.14, and Thunderbird 140.2.

## Affected

- `firefox < 128.14.0`
- `firefox < 142.0`
- `firefox >= 140.0, < 140.2.0`
- `thunderbird < 128.14.0`
- `thunderbird < 142.0`
- `thunderbird >= 140.0, < 140.2.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.2.0`
- `thunderbird 140.2.0`