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Nginx UiWeb server / proxy · Nginxui

CVE-2026-42221

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-04
Fix available
A fix is available. Upgrade to 2.3.8 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Nginx UI versions 2.0.0 through 2.3.7 have an unauthenticated install endpoint (/api/install) that allows remote attackers to claim the initial administrator account during first-run setup before the legitimate operator. The lack of authentication on this endpoint combined with the timing window enables permanent initial-instance takeover.

MitigationUpgrade to nginx-ui version 2.3.8 or later, and ensure the service is network-isolated from untrusted networks during initial setup to prevent pre-emptive admin account creation.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Nginx UiWeb server / proxy
Affected:>= 2.0.0, < 2.3.8

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify nginx-ui version
    Check the installed nginx-ui version. If using Docker, check the image tag; if using a package manager, run 'nginx-ui --version' or check the package version; if running from binary, check the binary or its metadata.
    Affected if The installed version is 2.0.0 through 2.3.7 inclusive.
  2. Verify admin account exists
    Check whether an administrator account has already been created. This can be done by querying the application database or configuration (commonly found in a SQLite database file or user configuration file in the application data directory). Look for entries indicating an admin user or superuser exists.
    Affected if No admin account exists yet, meaning the application is in a first-run setup state and the /api/install endpoint would be active.
  3. Assess network exposure of /api/install
    Test whether the /api/install endpoint is accessible from the network. Use a curl command such as: curl -s -o /dev/null -w '%{http_code}' http://<your-server>/api/install or equivalent HTTP request to check for a response. If the service is behind a reverse proxy, ensure the check reaches the nginx-ui service directly.
    Affected if The endpoint returns an HTTP response (any status code) indicating it is reachable, rather than a 404 or connection refused error.
  4. Check initial setup completion status
    Inspect the application's state file or database for a flag or record indicating whether initial setup has been completed. Many applications store a 'initialized', 'setup_complete', or similar flag. Check configuration files, database files, or environment variables for this indicator.
    Affected if The application indicates initial setup has NOT been completed, leaving the /api/install endpoint active and exploitable.

You are affected if nginx-ui version 2.0.0-2.3.7 is running, the /api/install endpoint is network-accessible, and no administrator account has been created yet (first-run state).

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.3.8 or later
Fixed in 2.3.8
Interim mitigation

Upgrade to nginx-ui version 2.3.8 or later, and ensure the service is network-isolated from untrusted networks during initial setup to prevent pre-emptive admin account creation.

Recommended fix High confidence

2.3.8 or later

  1. Upgrade Nginx UI to version 2.3.8 or later to apply the security patch that adds authentication to the /api/install endpoint

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Nginx Ui Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42221 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data