CVE-2026-42222

Nginx-UI: Unauthenticated first-boot instance claim via POST /api/install allows remote bootstrap takeover

This issue allows full unauthenticated takeover of a fresh nginx-ui instance during the initial installation window.

The practical exposure window is limited, but the impact inside that window is complete administrative takeover. An attacker does not need to guess defaults or exploit an authenticated feature; they become the first administrator and define the instance trust material themselves.

In live testing, the attacker was able to:

• confirm that the target was still uninitialized
• submit attacker-chosen bootstrap credentials
• lock the installation under attacker control
• immediately authenticate as the newly set administrator

Observed values during live reproduction included:

INSTALL_BEFORE={"lock":false,"timeout":false}
INSTALL_POST={"message":"ok"}
INSTALL_AFTER={"lock":true,"timeout":false}
LOGIN_RESPONSE={"message":"ok","code":200,...,"short_token":"qIJAE3dQMm3afhaV"}

Because the bootstrap request also initializes the application's trust material, this is more severe than a simple default-admin issue. An attacker does not merely guess credentials; they define the initial administrator account and application secrets themselves.

A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.

CVE-2026-42222 has a CVSS score of 8.1 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. What is CVE-2026-42222? CVE-2026-42222 is a high-severity missing authentication for critical function vulnerability in github.com/0xJacky/nginx-ui (go), affecting versions = 2.3.5. No fixed version is listed yet. A critical operation is accessible without requiring any authentication.
2. How severe is CVE-2026-42222? CVE-2026-42222 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/0xJacky/nginx-ui are affected by CVE-2026-42222? github.com/0xJacky/nginx-ui (go) versions = 2.3.5 is affected.
4. Is there a fix for CVE-2026-42222? No fixed version is listed for CVE-2026-42222 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-42222 exploitable, and should I be worried? Whether CVE-2026-42222 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42222 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-42222? No fixed version is listed yet. In the interim: Keep the dependency up to date. Add authentication gating to all sensitive endpoints.