High-severity RCE-like JIT memory bug in Firefox/Thunderbird — widely used client software that warrants broad IT notice.
CVE-2026-100814
Firefox/Thunderbird JIT memory-bounds bug enabling remote code execution.
Is CVE-2026-100814 being exploited?
Not confirmed. CVE-2026-100814 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.
How severe is CVE-2026-100814?
CVE-2026-100814 is rated High with a CVSS score of 8.8. 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-2026-100814?
Yes. A fix has been recorded for CVE-2026-100814. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100814 affect?
CVE-2026-100814 affects Firefox < 157, Firefox ESR < 153.4, Thunderbird < 157, Thunderbird ESR < 153.4. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100814?
Upgrade Firefox/Thunderbird to the specified fixed versions immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Memory-corruption in JS JIT enabling remote code execution via crafted web content or messages.
Immediate action required