# CVE-2026-42221: GO-2026-5412 - Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim in github.com/0xJacky/Nginx-UI

Source: https://junglewise.ai/threats/cve-2026-42221-nginx-ui-unauthenticated-first-run-installer-allows-remote  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-04  
License: CC BY 4.0 with a link back

CVE-2026-42221 · Severity: high · CVSS 8.1 · Published 2026-05-04

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.

Technologies: [github.com/0xJacky/Nginx-UI (Go)](https://junglewise.ai/threats/technologies/github-com-0xjacky-nginx-ui), [Nginxui Nginx Ui](https://junglewise.ai/threats/technologies/nginxui-nginx-ui). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Nginxui](https://junglewise.ai/threats/vendors/nginxui).

## Quick answers

**Is CVE-2026-42221 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42221 being exploited in the wild.

**How severe is CVE-2026-42221?** High severity, with a CVSS score of 8.1, published 4 May 2026.

**Which products and versions are affected?** github.com/0xJacky/Nginx-UI (Go) SEMVER:introduced=0, SEMVER:introduced=2.0.0,fixed=2.3.8.

**Is there a fix for CVE-2026-42221?** Yes. github.com/0xJacky/Nginx-UI (Go): upgrade to 2.3.8 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-42221?** Check whether you run github.com/0xJacky/Nginx-UI (Go) or Nginxui Nginx Ui at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/0xJacky/Nginx-UI (Go): upgrade to 2.3.8 or later

  ```sh
  go get github.com/0xJacky/Nginx-UI@v2.3.8
  ```


## Affected products

- github.com/0xJacky/Nginx-UI (Go) SEMVER:introduced=0, SEMVER:introduced=2.0.0,fixed=2.3.8
- Nginxui Nginx Ui

## Identifiers

- CVE-2026-42221
- GHSA-h27v-ph7w-m9fp
- GO-2026-5412

## Related threats

- [Nginx UI Casdoor SSO login CSRF via constant state parameter](https://junglewise.ai/threats/cve-2026-84312-nginx-ui-casdoor-sso-callback-uses-a-constant-state-parameter)
- [Nginx UI OTP secure-session step-up bypass via MCP](https://junglewise.ai/threats/cve-2026-84360-nginx-ui-otp-secure-session-step-up-can-be-bypassed-via-mcp)
- [Nginx UI short token cache bypass after account re-enable](https://junglewise.ai/threats/cve-2026-84321-nginx-ui-standalone-short-tokens-survive-administrative)
- [Nginx UI auto backup path traversal in storage boundary](https://junglewise.ai/threats/cve-2026-84320-nginx-ui-auto-backup-name-allows-path-traversal-outside-validated)
- [Nginx UI MCP configuration directive validation bypass](https://junglewise.ai/threats/cve-2026-84319-nginx-ui-mcp-configuration-tools-bypass-restricted-directive)