CVE-2026-84140
Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
- Published Sep 1, 2026
- CVSS 9.8 critical
- 0.3% chance of exploitation in the next 30 days (EPSS)
- A fix is available