9.8

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

Analyzed
AliasesGHSA-h27v-ph7w-m9fpGO-2026-5412
Published 04-05-2026Last modified 05-05-2026

Vulnerability summary

CVE-2026-42221 is a critical (CVSS 9.8) vulnerability in 0xjacky nginx-ui. EPSS estimates a 1.34% chance of exploitation in the next 30 days, higher than 71.3% of scored vulnerabilities. 1 public exploit is recorded.

Priority
Prioritisepublic exploit

Public exploit (GitHub, Date unknown)

Source freshness unavailable

How is this decided?
CVSS score
9.8/10
010
Critical · v3.1 (NVD)
EPSS score
1.34%
0%100%
Low · -0.26 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits1github

Advisory lineage

Upstream 0 · Downstream 1 · Related 1
OPENSUSE-SU-2026:21483-1

Timeline

  1. 04-05-2026
    PublishedVulnerability first disclosed.
  2. 05-05-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

1.34%

Chance of exploitation in the next 30 days

Percentile

71%

Versus all other CVEs

30-day change

Decrease -0.26 pp

From 1.60% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

1 found
  • githubUnverified

    Nginx Ui

    Maturity: poc

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

0xjacky1 product
Github.com/0xJacky1 product
  • Nginx-UI≥ 2.0.0, < 2.3.8 | All versions (No fix recorded)
Nginxui1 product

3 vendors · 3 products

References

4 links