High-severity sandbox escape in Mozilla Firefox — widely used browser; enables remote code execution and is newsworthy for IT orgs.
CVE-2026-100811
Firefox DOM use-after-free allows sandbox escape and remote code execution.
Is CVE-2026-100811 being exploited?
Not confirmed. CVE-2026-100811 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-2026-100811?
CVE-2026-100811 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-2026-100811?
Yes. A fix has been recorded for CVE-2026-100811. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100811 affect?
CVE-2026-100811 affects Firefox <157, Firefox ESR <153.4, Firefox ESR <140.17. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100811?
Update Firefox to 157, ESR 153.4 or ESR 140.17 immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
DOM use-after-free leads to sandbox escape enabling remote arbitrary code execution in affected Firefox versions.
Immediate action required