Affects widely-used Firefox/Thunderbird with CVSS 9.8; DOM security bypass could impact many organizations.
CVE-2026-2784
DOM mitigation bypass in Firefox/Thunderbird browsers.
Is CVE-2026-2784 being exploited?
Not confirmed. CVE-2026-2784 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 0.43% probability of exploitation in the next 30 days.
How severe is CVE-2026-2784?
CVE-2026-2784 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-2026-2784?
Yes. A fix has been recorded for CVE-2026-2784. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-2784 affect?
CVE-2026-2784 affects Mozilla Firefox < 148, Firefox ESR < 140.8, Mozilla Thunderbird < 148, Thunderbird < 140.8. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-2784?
Update to latest Firefox/Thunderbird when patch is released
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypass of DOM security mitigations enabling DOM-based attacks and potential cross-origin data access.
Immediate action required