Browser sandbox escape in Mozilla Firefox enables remote arbitrary code execution in a widely deployed application, posing enterprise-wide desktop and data risk that requires broad IT action.
CVE-2026-100818
Firefox sandbox escape (Gtk use-after-free) enabling arbitrary code execution.
Is CVE-2026-100818 being exploited?
Not confirmed. CVE-2026-100818 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.
How severe is CVE-2026-100818?
CVE-2026-100818 is rated Critical with a CVSS score of 9.6. 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-2026-100818?
Yes. A fix has been recorded for CVE-2026-100818. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100818 affect?
CVE-2026-100818 affects Mozilla Firefox (desktop, Gtk builds), Firefox < 157, Firefox ESR < 153.4, Firefox ESR 140 < 140.17. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100818?
Update to Firefox 157+ or ESR 153.4/140.17+ immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Escape Firefox sandbox via a Gtk use-after-free to execute arbitrary code as the user from crafted web content.
Immediate action required