Affects widely deployed Mozilla products; bypasses enterprise policy controls protecting endpoints and configurations.
CVE-2026-16390
Mitigation bypass in Mozilla Enterprise Policies for Firefox and Thunderbird.
Is CVE-2026-16390 being exploited?
Not confirmed. CVE-2026-16390 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 0.32% probability of exploitation in the next 30 days.
How severe is CVE-2026-16390?
CVE-2026-16390 is rated Critical with a CVSS score of 9.1. 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-2026-16390?
Yes. A fix has been recorded for CVE-2026-16390. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16390 affect?
CVE-2026-16390 affects Firefox < 153, Firefox ESR < 140.13, Thunderbird < 153, Thunderbird ESR < 140.13. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16390?
Update to Firefox/Thunderbird patched versions (153 / ESR 140.13+) immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypasses enterprise policy enforcement, allowing attackers to alter settings, install extensions, disable protections, or maintain persistence.
Immediate action required