CVE-2026-84128
Privilege escalation in WebDriver BiDi fixed in Firefox/Thunderbird 155.
Is CVE-2026-84128 being exploited?
Not confirmed. CVE-2026-84128 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-2026-84128?
CVE-2026-84128 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-2026-84128?
Yes. A fix has been recorded for CVE-2026-84128. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-84128 affect?
CVE-2026-84128 affects Mozilla Firefox <155, Mozilla Thunderbird <155, WebDriver BiDi component. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-84128?
Update Firefox and Thunderbird to 155+ immediately; restrict automated WebDriver access.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attackers can exploit WebDriver BiDi to escalate privileges or escape browser sandbox, enabling higher-privilege code execution on affected hosts.
Patch when possible