CVE-2026-16381
Same-origin bypass in Firefox/Thunderbird DNS enabling cross-origin data exposure.
Is CVE-2026-16381 being exploited?
Not confirmed. CVE-2026-16381 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 0.17% probability of exploitation in the next 30 days.
How severe is CVE-2026-16381?
CVE-2026-16381 is rated Critical with a CVSS score of 9.1. 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-2026-16381?
Yes. A fix has been recorded for CVE-2026-16381. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16381 affect?
CVE-2026-16381 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-2026-16381?
Update Firefox/Thunderbird to 153 or ESR 140.13+ immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote sites can bypass same-origin checks to read cross-origin resources, exfiltrate sensitive data, or hijack sessions in affected browsers.
Immediate action required