CVE-2026-8955
Privilege escalation in Firefox DOM Workers; fixed in Firefox 151/ESR 140.11 and Thunderbird 151.
Is CVE-2026-8955 being exploited?
Not confirmed. CVE-2026-8955 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 0.39% probability of exploitation in the next 30 days.
How severe is CVE-2026-8955?
CVE-2026-8955 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-2026-8955?
Yes. A fix has been recorded for CVE-2026-8955. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-8955 affect?
CVE-2026-8955 affects Mozilla Firefox, Mozilla Firefox ESR, Mozilla Thunderbird. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-8955?
Update to Firefox 151+ and Thunderbird 151+
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Browser DOM Workers privilege escalation; could allow higher-privilege actions in the browser process.
Patch when possible