CVE-2026-42221: Nginxui Nginx UI

Critical severity, CVSS 9.8. EPSS: 1.6% chance of exploitation in the next 30 days.

Nginx UI is a web user interface for the Nginx web server. From version 2.0.0 to before version 2.3.8, an unauthenticated network attacker can claim the initial administrator account on a fresh nginx-ui instance during the first-run setup window. The public /api/install endpoint is reachable without authentication, and the request-encryption flow only protects payload confidentiality in transit; it does not authenticate who is allowed to perform installation. A remote attacker who reaches the service before the legitimate operator can set the admin email, username, and password, causing permanent initial-instance takeover. This issue has been patched in version 2.3.8.

Affected products

• Nginxui Nginx UI: from 2.0.0, before 2.3.8 (fixed in 2.3.8)

Published 2026-05-04. Last modified 2026-06-17.