CVE-2026-74955
Privilege escalation in Firefox/Thunderbird Request Handling (fixed in Firefox 154).
Is CVE-2026-74955 being exploited?
Not confirmed. CVE-2026-74955 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 0.22% probability of exploitation in the next 30 days.
How severe is CVE-2026-74955?
CVE-2026-74955 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-2026-74955?
Yes. A fix has been recorded for CVE-2026-74955. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74955 affect?
CVE-2026-74955 affects Firefox <154, Firefox ESR <153.1, Thunderbird <154, Thunderbird <153.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74955?
Upgrade to Firefox 154 or ESR 153.1 and Thunderbird 154 (or later)
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Local privilege escalation allowing an attacker with local or sandboxed code to gain higher privileges or escape sandbox, enabling elevated actions on the host.
Patch when possible