CVE-2026-74956: Mozilla Firefox

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

Same-origin policy bypass in the DOM: Service Workers component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

Affected products

• Mozilla Firefox: before 153.1.0 (fixed in 153.1.0); before 154.0.0 (fixed in 154.0.0)
• Mozilla Thunderbird: before 153.1.0 (fixed in 153.1.0); before 154.0 (fixed in 154.0)

Published 2026-08-18. Last modified 2026-08-19.