CVE-2025-4083: Mozilla Firefox

Critical severity, CVSS 9.1. EPSS: 0.5% chance of exploitation in the next 30 days.

A process isolation vulnerability in Thunderbird stemmed from improper handling of javascript: URIs, which could allow content to execute in the top-level document's process instead of the intended frame, potentially enabling a sandbox escape. This vulnerability was fixed in Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, and Thunderbird 128.10.

Affected products

• Mozilla Firefox: before 115.23 (fixed in 115.23); before 138.0 (fixed in 138.0); from 128.0, before 128.10 (fixed in 128.10)
• Mozilla Thunderbird: before 128.10.0 (fixed in 128.10.0); before 138.0 (fixed in 138.0)

Published 2025-04-29. Last modified 2026-10-05.