CVE-2026-4729
Memory safety bugs in Firefox 148 and Thunderbird 148 may allow arbitrary code execution.
Is CVE-2026-4729 being exploited?
Not confirmed. CVE-2026-4729 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 0.33% probability of exploitation in the next 30 days.
How severe is CVE-2026-4729?
CVE-2026-4729 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-2026-4729?
Yes. A fix has been recorded for CVE-2026-4729. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4729 affect?
CVE-2026-4729 affects Mozilla Firefox, Mozilla Thunderbird. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-4729?
Update to latest Firefox/Thunderbird once fix is released; enable auto-update.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution via memory corruption in Firefox <149 and Thunderbird <149.
Patch when possible