High-severity sandbox escape in widely used Mozilla Firefox/Thunderbird enabling host code execution; affects many users and has available fixes warranting broad IT notification.
CVE-2026-16356
Use-after-free in Disability Access APIs allows Firefox/Thunderbird sandbox escape.
Is CVE-2026-16356 being exploited?
Not confirmed. CVE-2026-16356 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-2026-16356?
CVE-2026-16356 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-2026-16356?
Yes. A fix has been recorded for CVE-2026-16356. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-16356 affect?
CVE-2026-16356 affects Mozilla Firefox < 153, Firefox ESR < 115.38, Firefox ESR < 140.13, Mozilla Thunderbird < 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-2026-16356?
Upgrade to Firefox 153 / ESR 115.38 or 140.13 and Thunderbird 153/140.13 immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Sandbox escape enabling arbitrary code execution on host via crafted web content or email, leading to full compromise.
Immediate action required