CVE-2026-74978
Clickjacking in Firefox/Thunderbird Widget allows UI redress attacks.
Is CVE-2026-74978 being exploited?
Not confirmed. CVE-2026-74978 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 0.23% probability of exploitation in the next 30 days.
How severe is CVE-2026-74978?
CVE-2026-74978 is rated High with a CVSS score of 8.1. 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-2026-74978?
Yes. A fix has been recorded for CVE-2026-74978. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74978 affect?
CVE-2026-74978 affects Mozilla Firefox <154, Firefox ESR <153.1, Mozilla Thunderbird <154, Thunderbird ESR <153.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74978?
Upgrade to Firefox/Thunderbird 154 or ESR 153.1+ immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
UI redress (clickjacking) lets attackers trick users into clicking hidden controls to change settings, authorize actions, or trigger downloads.
Patch when possible