CVE-2026-4692

38th percentile - higher than 38% of all known CVEs

A sandbox escape vulnerability exists in the Responsive Design Mode component. This flaw was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

An attacker could exploit this vulnerability to break out of the browser sandbox and gain access to the underlying operating system, potentially leading to full device compromise or data theft.

Immediately update Firefox to version 149 or later, and Thunderbird to version 149 or 140.9. For ESR users, apply updates to 115.34 or 140.9 accordingly.