CVE-2026-4720
Memory safety bugs in Firefox/Thunderbird may allow arbitrary code execution.
Is CVE-2026-4720 being exploited?
Not confirmed. CVE-2026-4720 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 0.42% probability of exploitation in the next 30 days.
How severe is CVE-2026-4720?
CVE-2026-4720 is rated Low with a CVSS score of 3.1. 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-2026-4720?
Yes. A fix has been recorded for CVE-2026-4720. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4720 affect?
CVE-2026-4720 affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, Thunderbird < 140.9. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-4720?
Update to latest Firefox/Thunderbird.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Memory corruption could allow remote code execution via Firefox/Thunderbird.
Patch when possible