Broad impact on widely used Firefox/Thunderbird clients; critical RCE risk via DOM WebIDL UAF.
CVE-2026-2770
Use-after-free in Firefox/Thunderbird DOM WebIDL bindings.
Is CVE-2026-2770 being exploited?
Not confirmed. CVE-2026-2770 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 0.47% probability of exploitation in the next 30 days.
How severe is CVE-2026-2770?
CVE-2026-2770 is rated Critical with a CVSS score of 9.8. 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-2026-2770?
Yes. A fix has been recorded for CVE-2026-2770. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-2770 affect?
CVE-2026-2770 affects Firefox < 148, Firefox ESR < 115.33, Firefox ESR < 140.8, Thunderbird < 148, 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-2026-2770?
Update to latest Firefox/Thunderbird
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via crafted content exploiting DOM WebIDL use-after-free.
Patch when possible