CVE-2026-21891 CRITICAL

CVE-2026-21891: ZimaOS has Authentication Bypass via System-Level Username

Vendor Icewhaletech
Product ZimaOS
Weakness CWE-287 · Improper authentication
Published January 8, 2026
Last update January 8, 2026

CVSS base score

9.4/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality High
Integrity High

CVSS vector

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

What the vulnerability does

01Description

ZimaOS is a fork of CasaOS, an operating system for Zima devices and x86-64 systems with UEFI. In versions up to and including 1.5.0, the application checks the validity of the username but appears to skip, misinterpret, or incorrectly validate the password when the provided username matches a known system service account. The application's login function fails to properly handle the password validation result for these users, effectively granting authenticated access to anyone who knows one of these common usernames and provides any password. As of time of publication, no known patched versions are available.

Key dates

02Disclosure timeline

January 8, 2026 CVE published
January 8, 2026 Record updated