CVE-2026-4690
Sandbox escape in Firefox/Thunderbird XPCOM boundary overflow.
Is CVE-2026-4690 being exploited?
Not confirmed. CVE-2026-4690 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 0.77% probability of exploitation in the next 30 days.
How severe is CVE-2026-4690?
CVE-2026-4690 is rated High with a CVSS score of 8.6. 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-2026-4690?
Yes. A fix has been recorded for CVE-2026-4690. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4690 affect?
CVE-2026-4690 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-2026-4690?
Update to latest Firefox/Thunderbird (149+) or ESR versions (115.34+/140.9+).
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Sandbox escape enabling code execution outside browser sandbox via XPCOM overflow.
Patch when possible