CVE-2026-42221

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

Nginx-Ui

Nginxui Nginx Ui

< 2.3.8

Fix

Available

CVSS 3.1

9.8 CRITICAL

EPSS

0.3% (27th percentile)

Weakness

CWE-306

NVD status

Analyzed

Published

2026-05-04