Widely used browser (Mozilla Firefox) with a sandbox escape enabling remote code execution; broad enterprise impact and urgent patching required.
CVE-2026-100778
Firefox DOM use-after-free sandbox escape enabling remote code execution.
Is CVE-2026-100778 being exploited?
Not confirmed. CVE-2026-100778 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-2026-100778?
CVE-2026-100778 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-2026-100778?
Yes. A fix has been recorded for CVE-2026-100778. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100778 affect?
CVE-2026-100778 affects Mozilla Firefox (desktop) versions prior to 157, Firefox ESR releases prior to 153.4, 140.17, and 115.42. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100778?
Update Firefox to the listed fixed versions immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Sandbox escape via DOM use-after-free allowing arbitrary code execution and full host compromise through the browser.
Immediate action required