CVE-2026-74939
Privilege escalation in DOM navigation in Firefox/Thunderbird allowing elevated in‑browser privileges.
Is CVE-2026-74939 being exploited?
Not confirmed. CVE-2026-74939 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-2026-74939?
CVE-2026-74939 is rated High with a CVSS score of 8.8. 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-2026-74939?
Yes. A fix has been recorded for CVE-2026-74939. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74939 affect?
CVE-2026-74939 affects Mozilla Firefox < 154, Firefox ESR prior to 115.39 / 140.14 / 153.1, Mozilla Thunderbird < 154, Thunderbird ESR prior to 140.14 / 153.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74939?
Update Firefox/Thunderbird to v154 or the listed ESR fixes immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attackers can escalate DOM privileges via the Navigation component, enabling elevated in‑browser actions, potential data access or privileged operations.
Immediate action required