CVE-2026-42221

Name: CVE-2026-42221
Creator: NVD / NIST
Published: 2026-05-04T21:16:32.023+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 0.35%

Last modified Jun 17, 2026

CVE-2026-42221 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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. EPSS estimates a 0.35% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

0.35%

26.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-306

Affected Software

Vendor	Product	Versions
Nginxui	Nginx Ui	>= 2.0.0, < 2.3.8

References

https://github.com/0xJacky/nginx-ui/releases/tag/v2.3.8Release Notes
https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fpExploit, Mitigation, Vendor Advisory
https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fpExploit, Mitigation, Vendor Advisory

Timeline

Published: May 4, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-42221?

How severe is CVE-2026-42221?

CVE-2026-42221 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.35% probability of exploitation in the next 30 days.

How do I fix CVE-2026-42221?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-42221?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST