CVE-2026-74940
Use-after-free in Firefox/Thunderbird text rendering enabling remote code execution.
Is CVE-2026-74940 being exploited?
Not confirmed. CVE-2026-74940 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 0.41% probability of exploitation in the next 30 days.
How severe is CVE-2026-74940?
CVE-2026-74940 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-2026-74940?
Yes. A fix has been recorded for CVE-2026-74940. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74940 affect?
CVE-2026-74940 affects Mozilla Firefox prior to 154, Firefox ESR prior to 115.39 / 140.14 / 153.1, Thunderbird prior to 154, Thunderbird ESR prior to 140.14 / 153.1. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74940?
Update Firefox and Thunderbird to the listed patched versions immediately
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote arbitrary code execution via crafted web pages or email content; attacker can execute code in the browser/email process.
Immediate action required