Affects widely used Firefox/Thunderbird with a sandbox escape enabling potential RCE.
CVE-2026-4692
Sandbox escape in Firefox/Thunderbird Responsive Design Mode
Is CVE-2026-4692 being exploited?
Not confirmed. CVE-2026-4692 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.49% probability of exploitation in the next 30 days.
How severe is CVE-2026-4692?
CVE-2026-4692 is rated Critical with a CVSS score of 10.0. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-4692?
Yes. A fix has been recorded for CVE-2026-4692. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4692 affect?
CVE-2026-4692 affects Firefox <149, Firefox ESR <115.34, Firefox ESR <140.9, Thunderbird <149, and 1 further product or version. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-4692?
Patch when available; monitor advisories and consider RDMode restrictions.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Arbitrary code execution in the browser process via sandbox escape; potential OS compromise.
Patch when possible