Widely used Firefox/Thunderbird; sandbox escape could enable remote code execution across endpoints, impacting multiple industries.
CVE-2026-2776
Sandbox escape in Telemetry allows browser RCE in Firefox/Thunderbird
Is CVE-2026-2776 being exploited?
Not confirmed. CVE-2026-2776 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 0.48% probability of exploitation in the next 30 days.
How severe is CVE-2026-2776?
CVE-2026-2776 is rated Critical with a CVSS score of 10.0. 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-2026-2776?
Yes. A fix has been recorded for CVE-2026-2776. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-2776 affect?
CVE-2026-2776 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-2026-2776?
Update to latest Firefox/Thunderbird; apply patch; disable Telemetry if feasible
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Sandbox escape enables arbitrary code execution in the browser context via Telemetry boundary flaw.
Patch when possible