CVE-2026-4717
Privilege escalation in Firefox/Thunderbird Netmonitor before fixed versions.
Is CVE-2026-4717 being exploited?
Not confirmed. CVE-2026-4717 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-2026-4717?
CVE-2026-4717 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-2026-4717?
Yes. A fix has been recorded for CVE-2026-4717. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4717 affect?
CVE-2026-4717 affects Mozilla Firefox <= 149, Mozilla Firefox ESR <= 140.9, Mozilla Thunderbird <= 149, Mozilla Thunderbird <= 140.9. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-4717?
Patch when available; enable auto-updates; sandbox Netmonitor if feasible.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Local privilege escalation via Netmonitor; could grant SYSTEM/administrator on host.
Patch when possible