Browser engine vulnerability in widely used Firefox/Thunderbird can enable remote code execution; affects many users and enterprise endpoints, warrants org-wide notice.
CVE-2026-100773
Use-after-free in IndexedDB in Firefox/Thunderbird enabling potential remote code execution
Is CVE-2026-100773 being exploited?
Not confirmed. CVE-2026-100773 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-2026-100773?
CVE-2026-100773 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-2026-100773?
Yes. A fix has been recorded for CVE-2026-100773. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-100773 affect?
CVE-2026-100773 affects Mozilla Firefox (fixed in 157; ESR fixes: 153.4, 140.17, 115.42), Mozilla 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-2026-100773?
Apply Mozilla updates to the fixed versions immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Use-after-free in IndexedDB can lead to remote code execution or sandbox escape via crafted web content.
Immediate action required