CVE-2026-4711
Use-after-free in Mozilla Cocoa Widget; affects Firefox/Thunderbird older releases.
Is CVE-2026-4711 being exploited?
Not confirmed. CVE-2026-4711 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 0.40% probability of exploitation in the next 30 days.
How severe is CVE-2026-4711?
CVE-2026-4711 is rated Critical with a CVSS score of 9.8. 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-2026-4711?
Yes. A fix has been recorded for CVE-2026-4711. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4711 affect?
CVE-2026-4711 affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, Thunderbird < 140.9. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-4711?
Monitor and apply patch when released
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Potential arbitrary code execution or crash via memory corruption in browser UI.
Monitor only