Affects widely used Mozilla Firefox and Thunderbird; critical mitigation bypass enabling potential remote code execution across organizations and users.
CVE-2026-74938
Mitigation bypass in Firefox/Thunderbird JavaScript GC enabling potential remote code execution.
Is CVE-2026-74938 being exploited?
Not confirmed. CVE-2026-74938 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 0.32% probability of exploitation in the next 30 days.
How severe is CVE-2026-74938?
CVE-2026-74938 is rated Critical with a CVSS score of 9.1. 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-2026-74938?
Yes. A fix has been recorded for CVE-2026-74938. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74938 affect?
CVE-2026-74938 affects Firefox < 154, Firefox ESR < 153.1, Thunderbird < 154, Thunderbird ESR < 153.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74938?
Update Firefox/Thunderbird to fixed versions immediately; restrict untrusted content and apply standard mitigations.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Bypasses JavaScript GC mitigations to achieve remote code execution via crafted web content or email, enabling arbitrary code execution and system compromise.
Immediate action required