CVE-2026-2777: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 0.6% chance of exploitation in the next 30 days.

Privilege escalation in the Messaging System component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Affected products

• Mozilla Firefox: before 115.33.0 (fixed in 115.33.0); before 148.0 (fixed in 148.0); from 128.0, before 140.8.0 (fixed in 140.8.0)
• Mozilla Thunderbird: before 140.8.0 (fixed in 140.8.0); before 148.0 (fixed in 148.0)

Published 2026-02-24. Last modified 2026-07-15.