Auth bypass in 0xjacky Nginx-Ui
CVE-2026-42221
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.
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.016 (75.4th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 75th percentile — 75.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.012 · newest: 0.016 · change: +0.004
Affected products
- 0xjacky Nginx-Ui — versions >= 2.0.0, < 2.3.8
- Nginxui nginx Ui
Weakness classification (CWE)
Public proof-of-concept exploits
References
- github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fp (Exploit, Mitigation, Vendor Advisory)
- github.com/0xJacky/nginx-ui/releases/tag/v2.3.8 (Release Notes)
Frequently asked questions
- What is CVE-2026-42221?
- CVE-2026-42221 is a high-severity vulnerability in 0xjacky Nginx-Ui, classified under Missing Authentication for Critical Function. CVSS score: 8.1/10. Published 2026-05-04.
- How severe is CVE-2026-42221?
- High severity. CVSS v3 base score is 8.1 out of 10.
- Is CVE-2026-42221 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.