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CVE-2026-42221— nginx-ui: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

Quick assessment

Affected
0xJacky nginx-ui
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Nginx UI是Jacky个人开发者的一个 Nginx 的 WebUI。 Nginx UI 2.0.0版本至2.3.8之前版本存在访问控制错误漏洞，该漏洞源于首次运行设置期间公共/api/install端点无需认证，可能导致未认证网络攻击者声明初始管理员账户。

CVSS 8.1 · High EPSS 1.60% · P75

Public Exploits 1

Nuclei · 1 CVE-2026-42221.yaml [template]

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
0xJacky nginx-ui >= 2.0.0, < 2.3.8 affected
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I. Basic Information for CVE-2026-42221

Vulnerability Information
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Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

Vulnerability Title
nginx-ui: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
关键功能的认证机制缺失
Source: CVE Program / CVE List V5
Vulnerability Title
Nginx UI 访问控制错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Nginx UI是Jacky个人开发者的一个 Nginx 的 WebUI。 Nginx UI 2.0.0版本至2.3.8之前版本存在访问控制错误漏洞，该漏洞源于首次运行设置期间公共/api/install端点无需认证，可能导致未认证网络攻击者声明初始管理员账户。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
0xJacky nginx-ui >= 2.0.0, < 2.3.8 -

II. Public POCs for CVE-2026-42221

# POC Description Source Link Shenlong Link
1 Nginx UI 2.0.0 to 2.3.8 contains an authentication bypass caused by unauthenticated access to /api/install during first-run setup, letting remote attackers claim the initial admin account, exploit requires attacker to access the service before legitimate operator. https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-42221.yaml POC Details
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III. Intelligence Information for CVE-2026-42221

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Vendor Advisories for CVE-2026-42221 (1)

Other References for CVE-2026-42221 (1)

Same Patch Batch · 0xJacky · 2026-05-04 · 5 CVEs total

CVE-2026-42222 8.1 HIGH nginx-ui: Unauthenticated first-boot instance claim via POST /api/install allows remote bo
CVE-2026-42220 6.5 MEDIUM nginx-ui: Authenticated settings disclosure exposes node.secret and enables trusted-node a
CVE-2026-42223 6.5 MEDIUM nginx-ui: Settings API Exposes Protected Secrets
CVE-2026-42238 Unauthenticated Remote Code Execution via Backup Restore in nginx-ui

IV. Related Vulnerabilities

Same product: nginx-ui
Same vendor: 0xJacky
Same weakness: CWE-306

V. Comments for CVE-2026-42221

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