Critical RCE in widely used Mozilla desktop products (Firefox/Thunderbird) with CVSS 9.8; affects many enterprise endpoints and user systems.
CVE-2026-16369
Integer overflow in Firefox/Thunderbird WebAssembly allows remote code execution.
Is CVE-2026-16369 being exploited?
Not confirmed. CVE-2026-16369 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 0.44% probability of exploitation in the next 30 days.
How severe is CVE-2026-16369?
CVE-2026-16369 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-2026-16369?
Yes. A fix has been recorded for CVE-2026-16369. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16369 affect?
CVE-2026-16369 affects Mozilla Firefox < 153, Firefox ESR < 140.13, Mozilla Thunderbird < 153, Thunderbird ESR < 140.13. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16369?
Update to Firefox 153/ESR 140.13 and Thunderbird 153/140.13 immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via JavaScript/WebAssembly integer overflow in Firefox/Thunderbird; attackers can run arbitrary code and compromise endpoints.
Immediate action required