Affects widely used Firefox/Thunderbird; critical mitigation bypass in browser components enabling persistent/remote compromise across organizations.
CVE-2026-16407
Mitigation bypass in Service Workers allowing attacker-controlled background scripts.
Is CVE-2026-16407 being exploited?
Not confirmed. CVE-2026-16407 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 0.28% probability of exploitation in the next 30 days.
How severe is CVE-2026-16407?
CVE-2026-16407 is rated Critical with a CVSS score of 9.8. 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-2026-16407?
Yes. A fix has been recorded for CVE-2026-16407. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16407 affect?
CVE-2026-16407 affects Firefox <153, Thunderbird <153, Gecko-based apps using vulnerable DOM Service Workers. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16407?
Upgrade Firefox/Thunderbird to 153+ immediately; apply vendor updates.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypasses Service Worker protections to run attacker scripts in worker context, enabling persistent malicious background code, privilege escalation, data theft, or RCE.
Immediate action required