CVE-2026-16365
Privilege escalation in Firefox/Thunderbird Workers (fixed in 153)
Is CVE-2026-16365 being exploited?
Not confirmed. CVE-2026-16365 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-2026-16365?
CVE-2026-16365 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-2026-16365?
Yes. A fix has been recorded for CVE-2026-16365. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16365 affect?
CVE-2026-16365 affects Firefox <153, Thunderbird <153. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16365?
Update to Firefox/Thunderbird 153+ immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Crafted web content can exploit Workers to escalate privileges, enabling sandbox escape, access to privileged APIs, or code execution in the browser process.
Immediate action required