Critical sandbox escape in widely used Mozilla Firefox allowing host compromise via the browser; requires org-wide mitigation and rapid deployment.
CVE-2026-100804
Firefox use-after-free allows sandbox escape and potential code execution (fixed in 157)
Is CVE-2026-100804 being exploited?
Not confirmed. CVE-2026-100804 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-2026-100804?
CVE-2026-100804 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-2026-100804?
Yes. A fix has been recorded for CVE-2026-100804. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100804 affect?
CVE-2026-100804 affects Mozilla Firefox < 157. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100804?
Update to Firefox 157+ immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Use-after-free in Preferences backend enables sandbox escape and arbitrary code execution on the host via crafted content.
Immediate action required