CVE-2026-16351
Use-after-free sandbox escape in Firefox/Thunderbird enabling remote code execution.
Is CVE-2026-16351 being exploited?
Not confirmed. CVE-2026-16351 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 0.39% probability of exploitation in the next 30 days.
How severe is CVE-2026-16351?
CVE-2026-16351 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-2026-16351?
Yes. A fix has been recorded for CVE-2026-16351. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16351 affect?
CVE-2026-16351 affects Mozilla Firefox versions before 153, Firefox ESR before 115.38, Firefox ESR 140 before 140.13, Mozilla Thunderbird versions before 153, and 1 further product or version. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16351?
Update to Firefox/Thunderbird 153, ESR 115.38/140.13 or later immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via crafted web content; sandbox escape allows arbitrary code execution and potential system/user compromise.
Immediate action required