Missing Authentication for Critical Function in nginx-ui - CVE-2026-42221
Published: July 17, 2026
Vulnerability identifier: #VU138332
CSH Severity: High
CVSS v4: 9.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-42221
CWE-ID: CWE-306
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to claim the initial administrator account.
The vulnerability exists due to missing authentication for critical functionality in the /api/install installer endpoint when processing first-run installation requests on a fresh instance. A remote attacker can send a specially crafted installation request to claim the initial administrator account.
Exploitation is only possible before setup completes and within ten minutes of startup on an uninitialized instance.
Affected software
nginx-ui
How to mitigate CVE-2026-42221
Install security update from vendor's website.
nginx-ui - update to 2.3.8