CVE-2026-4718: Mozilla Firefox

High severity, CVSS 8.1. EPSS: 0.5% chance of exploitation in the next 30 days.

Undefined behavior in the WebRTC: Signaling component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Affected products

• Mozilla Firefox: before 140.9.0 (fixed in 140.9.0); before 149.0 (fixed in 149.0)
• Mozilla Thunderbird: before 140.9.0 (fixed in 140.9.0); before 149.0 (fixed in 149.0)

Published 2026-03-24. Last modified 2026-06-17.