CVE-2026-74960: Mozilla Firefox

High severity, CVSS 8.1. EPSS: 0.2% chance of exploitation in the next 30 days.

Site isolation issue in the WebExtensions component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

Affected products

• Mozilla Firefox: before 140.14.0 (fixed in 140.14.0); from 141.0, before 153.1.0 (fixed in 153.1.0)
• Mozilla Thunderbird: before 140.14.0 (fixed in 140.14.0); from 141.0, before 153.1.0 (fixed in 153.1.0)

Published 2026-08-18. Last modified 2026-08-24.