High-severity use-after-free enabling remote code execution in Mozilla Firefox — a widely used browser affecting many users and enterprise deployments; fixes released.
CVE-2026-100784
Use-after-free in Firefox text/fonts layout enabling remote code execution
Is CVE-2026-100784 being exploited?
Not confirmed. CVE-2026-100784 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 0.31% probability of exploitation in the next 30 days.
How severe is CVE-2026-100784?
CVE-2026-100784 is rated High with a CVSS score of 8.8. 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-2026-100784?
Yes. A fix has been recorded for CVE-2026-100784. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100784 affect?
CVE-2026-100784 affects Mozilla Firefox 157, Firefox ESR 153.4, Firefox ESR 140.17, Firefox ESR 115.42, 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-2026-100784?
Update Firefox to patched versions ASAP and restrict untrusted content.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote arbitrary code execution via crafted web content or fonts, enabling code execution in browser context and possible sandbox escape.
Immediate action required