Affects widely used Mozilla Firefox and Thunderbird (including ESR); DOM use-after-free can enable remote code execution across organizations.
CVE-2026-100774
DOM use-after-free in Firefox/Thunderbird enabling possible remote code execution.
Is CVE-2026-100774 being exploited?
Not confirmed. CVE-2026-100774 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-2026-100774?
CVE-2026-100774 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-2026-100774?
Yes. A fix has been recorded for CVE-2026-100774. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100774 affect?
CVE-2026-100774 affects Firefox (fixed in 157; ESR fixed in 153.4, 115.42, 140.17), Thunderbird (fixed in 157, 153.4, 140.17). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-100774?
Update Firefox/Thunderbird to the listed fixed versions immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Crafted web content or email can trigger a DOM use-after-free to achieve remote code execution or memory corruption.
Immediate action required