Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.1 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2026-42221: 1.34% estimated exploitation activity in the next 30 days; percentile 71.38 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details The vulnerable route is exposed publicly through the main API router. router/routers.go:61-70 mounts system.InitPublicRouter(root) under /api, and api/system/router.go:16-19 registers both GET /api/install and POST /api/install without AuthRequired(). The install handler only checks whether the instance is already installed and whether more than ten minutes have elapsed since startup. api/system/install.go:26-33 treats the instance as uninstalled…

Published by the source

6 May 2026, 16:59 UTC

Last modified by the source

6 May 2026, 16:59 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-h27v-ph7w-m9fp

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# Patch Next advisory brief: CVE-2026-42221

Advisory: Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim
IDs: CVE-2026-42221, GHSA-h27v-ph7w-m9fp
Record: https://patchnext.com/advisories/cve-2026-42221 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/0xJacky/Nginx-UI 2.3.8. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/0xJacky/Nginx-UI: affected >= 2.0.0, <= 2.3.5; fixed in 2.3.8

## Suggested inspection (read-only)
- Go github.com/0xJacky/Nginx-UI: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/0xJacky/Nginx-UI.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-h27v-ph7w-m9fp (GitHub-reviewed advisory GHSA-h27v-ph7w-m9fp lists affected ranges: Go github.com/0xJacky/Nginx-UI >=2.0.0 <=2.3.5)

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