CRITICAL CVSS 9.4
Published: 2026-01-08

CVE-2026-21891

zimaspace zimaos Security Advisory (CVE-2026-21891)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-21891 impacting zimaspace zimaos. Evaluated with CVSS Base Score of 9.4 (CRITICAL).

Original NVD Description

Source: NIST NVD
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.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
None (PR:N)
Unauthenticated execution
User Interaction
None (UI:N)
Zero human interaction required
Scope
Unchanged (S:U)
Confined to same security context
Confidentiality
High (C:H)
Total information disclosure
Integrity
High (I:H)
Total modification of target system
Availability
Low (A:L)
Partial service performance degradation

🎯 Affected Versions Matrix

Affected Product zimaspace / zimaos
Affected Versions *
Weakness Enumeration CWE-287

Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe

High-Intent Research Tool

Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2026-21891 impacting zimaspace zimaos.

⚡ Nuclei Detection Template (YAML) cve-2026-21891.yaml
id: cve-2026-21891

info:
  name: zimaspace zimaos - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: critical
  description: |
    Automated signature & scanner for CVE-2026-21891 affecting zimaspace zimaos.
    Evaluation: 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 ...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-21891
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L
    cvss-score: 9.4
    cve-id: CVE-2026-21891
    cwe-id: CWE-287
  tags: cve,cve-2026-21891,zimaspace,zimaos,critical

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "zimaos"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-21891.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-21891
# Target: zimaspace zimaos | CVSS: 9.4 (CRITICAL)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-21891 (zimaspace zimaos)...")
    headers = {
        "User-Agent": "CyberVault-Audit-Scanner/2.0",
        "Accept": "*/*"
    }
    try:
        r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
        print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
        if r.status_code < 500:
            print(f"[!] Target reachable. Verify version against zimaspace zimaos scope (*).")
        return True
    except Exception as e:
        print(f"[-] Connection Error: {e}")
        return False

if __name__ == '__main__':
    url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
    verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash) patch_cve-2026-21891.sh
# Recommended Remediation & Patching Commands for CVE-2026-21891
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install zimaos 2>/dev/null || \
sudo dnf upgrade zimaos 2>/dev/null || \
sudo yum update zimaos

# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i zimaos 2>/dev/null || rpm -qa | grep -i zimaos

# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."

🛡️ Remediation & Security Action

  • Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
  • Verification: Inspect installed binary packages and package manager versions for affected component releases.
  • Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.

🔗 Verified Technical References

Authorities
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Distributions
  • No records filed in this category.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2026-21891 in zimaspace zimaos?

Review vendor-specific security notices and update zimaspace zimaos packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.

Is there an active exploit or public PoC for CVE-2026-21891?

No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.

What is the CVSS 3.1 severity rating and impact for CVE-2026-21891?

CVE-2026-21891 is classified with a CVSS 3.1 Base Score of 9.4 (CRITICAL). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
9.4
CRITICAL SEVERITY
CVE ID CVE-2026-21891
Weakness CWE-287
Vendor zimaspace
Product zimaos
Published 2026-01-08
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L