High-severity browser RCE in widely deployed Mozilla Firefox including ESR builds; enterprise-wide patching required.
CVE-2026-100780
Use-after-free in Firefox DOM enabling potential remote code execution
Is CVE-2026-100780 being exploited?
Not confirmed. CVE-2026-100780 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-2026-100780?
CVE-2026-100780 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-2026-100780?
Yes. A fix has been recorded for CVE-2026-100780. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100780 affect?
CVE-2026-100780 affects Mozilla Firefox (desktop) prior to 157, Firefox ESR prior to 153.4 / 140.17 / 115.42. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100780?
Update Firefox to 157 or ESR 153.4/140.17/115.42 immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Crafted web content can trigger a use-after-free, causing crashes or allowing arbitrary code execution in the browser context.
Immediate action required