CVE-2026-74937
Use-after-free in Firefox/Thunderbird JS GC enabling remote code execution.
Is CVE-2026-74937 being exploited?
Not confirmed. CVE-2026-74937 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 0.29% probability of exploitation in the next 30 days.
How severe is CVE-2026-74937?
CVE-2026-74937 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-2026-74937?
Yes. A fix has been recorded for CVE-2026-74937. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74937 affect?
CVE-2026-74937 affects Mozilla Firefox <154, Firefox ESR <153.1, Mozilla 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-2026-74937?
Upgrade to Firefox 154 / ESR 153.1 and Thunderbird 154 / ESR 153.1 immediately.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via crafted JavaScript (use-after-free in JS GC); may allow arbitrary code execution or process crash, possible sandbox escape.
Immediate action required