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

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), Nginxui Nginx Ui. Vendors: Go, 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
    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

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