Affects widely used Mozilla products (Firefox/Thunderbird); critical privilege escalation (CVSS 9.8) that can disrupt endpoints and enterprise DLP controls — broadly relevant to all orgs.
CVE-2026-16401
Critical privilege escalation in Firefox/Thunderbird DLP component allowing local privilege gain.
Is CVE-2026-16401 being exploited?
Not confirmed. CVE-2026-16401 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 0.21% probability of exploitation in the next 30 days.
How severe is CVE-2026-16401?
CVE-2026-16401 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-2026-16401?
Yes. A fix has been recorded for CVE-2026-16401. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16401 affect?
CVE-2026-16401 affects Mozilla Firefox < 153, Mozilla Thunderbird < 153, Data Loss Prevention component. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16401?
Update Firefox and Thunderbird to 153+ immediately; restrict local access until patched.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Local attacker can escalate privileges via the Data Loss Prevention component, bypass DLP and gain higher OS privileges.
Immediate action required