Affects F5 BIG‑IP, a widely deployed enterprise load‑balancer; allows creation of administrative accounts leading to full appliance control—likely to impact many organizations.
CVE-2026-66842
Authenticated user can create admin accounts on F5 BIG‑IP via TMUI.
Is CVE-2026-66842 being exploited?
Not confirmed. CVE-2026-66842 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 0.28% probability of exploitation in the next 30 days.
How severe is CVE-2026-66842?
CVE-2026-66842 is rated High with a CVSS score of 8.7. 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-2026-66842?
Yes. A fix has been recorded for CVE-2026-66842. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-66842 affect?
CVE-2026-66842 affects F5 BIG-IP (TMUI / management interface). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-66842?
Apply F5 patch immediately; restrict TMUI to trusted networks, enable MFA, rotate creds.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Authenticated actor with network access to the BIG‑IP management interface can create administrative accounts and gain full control of the control plane.
Immediate action required
- affected>= 21.1.0 and < 21.1.0.1
- affected>= 21.0.0 and < 21.0.0.3
- affected>= 17.5.0 and < 17.5.1.8
- affected>= 17.1.0 and < 17.1.3.4
- affected>= 8.4.0 and < 8.4.2.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.