CVE-2026-16371
DOM Navigation privilege escalation in Firefox/Thunderbird allowing elevation of browser privileges.
Is CVE-2026-16371 being exploited?
Not confirmed. CVE-2026-16371 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 0.30% probability of exploitation in the next 30 days.
How severe is CVE-2026-16371?
CVE-2026-16371 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-2026-16371?
Yes. A fix has been recorded for CVE-2026-16371. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16371 affect?
CVE-2026-16371 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-2026-16371?
Upgrade to Firefox 153 / ESR 140.13 or Thunderbird 153 / ESR 140.13 immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Malformed web content can exploit a DOM Navigation flaw to escalate privileges in the browser process, enabling arbitrary code execution or elevated browser/extension access.
Immediate action required