Vulnerability Description
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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Nginxui | Nginx Ui | >= 2.0.0, < 2.3.8 |
Related Weaknesses (CWE)
References
- https://github.com/0xJacky/nginx-ui/releases/tag/v2.3.8Release Notes
- https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fpExploitMitigationVendor Advisory
- https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fpExploitMitigationVendor Advisory
FAQ
What is CVE-2026-42221?
CVE-2026-42221 is a vulnerability with a CVSS score of 8.1 (HIGH). 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-...
How severe is CVE-2026-42221?
CVE-2026-42221 has been rated HIGH with a CVSS base score of 8.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-42221?
Check the references section above for vendor advisories and patch information. Affected products include: Nginxui Nginx Ui.