Which products and versions are affected by CVE-2026-42221?

Affected: Nginx Ui (Nginxui) versions >= >= 2.0.0, = 2.0.0. The full list is in the CVE brief.

Is CVE-2026-42221 being exploited in the wild?

It is not listed in any known-exploited vulnerabilities catalog.

Is CVE-2026-42221 in the CISA KEV catalog?

No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.

Is there a public exploit for CVE-2026-42221?

Public exploit code is available.

Is there a fix for CVE-2026-42221?

Fixed versions are available, including github.com/0xJacky/Nginx-UI 2.3.8, Nginx Ui 2.3.8.

How urgently should CVE-2026-42221 be patched?

Brandefense priority: patch immediately, because public exploit code exists for a high-severity flaw.

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Vulnerability Intelligence

CVE-2026-42221

CriticalPublic exploit

Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

Published May 6, 2026 · Updated Sep 14, 2026 · Also known as GHSA-h27v-ph7w-m9fp, GO-2026-5412

Key Facts

Patch immediately

CVE-2026-42221 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting Nginx Ui (Nginxui), github.com/0xJacky/Nginx-UI (go).
It is not listed in any known-exploited vulnerabilities catalog. Public exploit code is available.
EPSS estimates a 1.6% probability of exploitation in the next 30 days.
Fixed versions are available, including github.com/0xJacky/Nginx-UI 2.3.8, Nginx Ui 2.3.8.
Brandefense priority: patch immediately, because public exploit code exists for a high-severity flaw.

CVSS v3.1

9.8

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

EPSS (30-day exploit likelihood)

1.6%

Higher than 75.4% of all scored CVEs

Exploited in the wild

No known

Not in a known-exploited catalog

Public exploit code

Available

Proof-of-concept or weaponized module

Get the full CVE-2026-42221 brief as a PDF

Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.

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.

Affected Products

3 affected entries in total

Product	Affected versions	Fixed in
Nginx UiNginxui	>= >= 2.0.0, < 2.3.8	2.3.8
github.com/0xJacky/Nginx-UIgo	>= 2.0.0	2.3.8

Patched Releases

github.com/0xJacky/Nginx-UI

2.3.8

Nginx Ui

2.3.8

Timeline

Publicly disclosed
May 6, 2026
Last updated
Sep 14, 2026

Weakness Type

CWE-306 Missing Authentication for Critical Function

References

1 more references in the full CVE brief

FAQ

Common Questions.

Nginx UI is a web user interface for the Nginx web server.
Affected: Nginx Ui (Nginxui) versions >= >= 2.0.0, < 2.3.8; github.com/0xJacky/Nginx-UI (go) versions >= 2.0.0. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
Public exploit code is available.
Fixed versions are available, including github.com/0xJacky/Nginx-UI 2.3.8, Nginx Ui 2.3.8.
Brandefense priority: patch immediately, because public exploit code exists for a high-severity flaw.

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