CVE-2026-42221
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.17%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 1.17% probability · 66th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-306
- Affected
- nginxui/nginx ui
- Source
- security-advisories@github.com
References
- https://github.com/0xJacky/nginx-ui/releases/tag/v2.3.8Release Notes
- https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fpExploit, Mitigation, Vendor Advisory
- https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fpExploit, Mitigation, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.