---
id: CVE-2025-4919
title: >-
  An attacker was able to perform an out-of-bounds read or write on a JavaScript
  object by confusing array index sizes
summary: >-
  An attacker was able to perform an out-of-bounds read or write on a JavaScript
  object by confusing array index sizes. This vulnerability was fixed in Firefox
  138.0.4, Firefox ESR 128.10.1, Firefox ESR 115.23.1, Thunderbird 128.10.2, and
  …
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-125
  - CWE-787
vendor: mozilla
product: firefox
affected:
  - firefox < 115.23.1
  - firefox < 138.0.4
  - 'firefox >= 116.0, < 128.10.1'
  - thunderbird < 128.10.2
  - 'thunderbird >= 138.0, < 138.0.2'
patched:
  - firefox 128.10.1
  - thunderbird 138.0.2
published: '2025-05-17'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-4919'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1966614'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-36/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-37/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-38/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-40/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-41/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/05/msg00046.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.08627
epssPercentile: 0.94937
ingestedAt: '2026-09-30T18:17:24.437Z'
---

## Overview

An attacker was able to perform an out-of-bounds read or write on a JavaScript object by confusing array index sizes. This vulnerability was fixed in Firefox 138.0.4, Firefox ESR 128.10.1, Firefox ESR 115.23.1, Thunderbird 128.10.2, and Thunderbird 138.0.2.

## Affected

- `firefox < 115.23.1`
- `firefox < 138.0.4`
- `firefox >= 116.0, < 128.10.1`
- `thunderbird < 128.10.2`
- `thunderbird >= 138.0, < 138.0.2`

## Remediation

Upgrade past the affected range:

- `firefox 128.10.1`
- `thunderbird 138.0.2`