High-severity sandbox escape enabling remote code execution in widely used Mozilla products (Firefox/Thunderbird), impacting many endpoints and likely to be urgent for all IT teams.
CVE-2026-16388
Sandbox escape in Firefox/Thunderbird enabling remote code execution.
Is CVE-2026-16388 being exploited?
Not confirmed. CVE-2026-16388 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 0.38% probability of exploitation in the next 30 days.
How severe is CVE-2026-16388?
CVE-2026-16388 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-2026-16388?
Yes. A fix has been recorded for CVE-2026-16388. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16388 affect?
CVE-2026-16388 affects Mozilla Firefox < 153, Mozilla Thunderbird < 153. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-16388?
Upgrade to Firefox/Thunderbird 153+ immediately; restrict untrusted content until patched.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution: crafted web or network content can escape the DOM sandbox to execute arbitrary code on the host.
Immediate action required