CVE-2025-4919: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 8.6% chance of exploitation in the next 30 days.

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 products

• Mozilla Firefox: before 115.23.1 (fixed in 115.23.1); before 138.0.4 (fixed in 138.0.4); from 116.0, before 128.10.1 (fixed in 128.10.1)
• Mozilla Thunderbird: before 128.10.2 (fixed in 128.10.2); from 138.0, before 138.0.2 (fixed in 138.0.2)

Published 2025-05-17. Last modified 2026-09-30.