Remote code execution in widely used Mozilla products (Firefox/Thunderbird) with CVSS 9.8; impacts many users and requires org-wide patching.
CVE-2026-16363
WebAssembly JIT miscompilation in Firefox/Thunderbird enabling remote code execution.
Is CVE-2026-16363 being exploited?
Not confirmed. CVE-2026-16363 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-2026-16363?
CVE-2026-16363 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-2026-16363?
Yes. A fix has been recorded for CVE-2026-16363. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16363 affect?
CVE-2026-16363 affects Firefox < 153, Firefox ESR < 140.13, 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-2026-16363?
Update to Firefox/Thunderbird patched versions immediately; block untrusted web content until patched.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via crafted web content/wasm exploiting JIT miscompile, enabling arbitrary code execution or sandbox escape.
Immediate action required