Critical sandbox escape in widely used Mozilla products (Firefox/Thunderbird) enabling remote code execution and broad user compromise; merits org-wide notification.
CVE-2026-75874
Sandbox escape in Remote Settings Client enables remote code execution in Firefox/Thunderbird
Is CVE-2026-75874 being exploited?
Not confirmed. CVE-2026-75874 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 0.46% probability of exploitation in the next 30 days.
How severe is CVE-2026-75874?
CVE-2026-75874 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-2026-75874?
Yes. A fix has been recorded for CVE-2026-75874. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-75874 affect?
CVE-2026-75874 affects Firefox <154, Thunderbird <154, Mozilla products using Remote Settings Client. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-75874?
Upgrade to Firefox/Thunderbird 154+ immediately and patch all endpoints.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via Remote Settings Client sandbox escape, enabling full user‑level compromise and arbitrary code execution.
Immediate action required