Vulnerability report

Exploited in the wild High confidence Not in CISA KEV

CVE-2026-21891

ZimaOS Has Authentication Bypass

IceWhale Tech / ZimaOS · <= 1.5.0

Watch CVE-2026-21891 Browse KEV feed
Severity
CVSS 9.4 · Critical
Confidence
High
Exploit status
Exploited in the wild
EPSS
2.3%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-21891 is an unauthenticated vulnerability affecting IceWhale Tech ZimaOS. 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,...

Is it exploited?

Yes. Previdian tracks this CVE as a known exploited vulnerability. Confidence is high. Also confirmed by third-party sources.

Who is affected?

IceWhale Tech / ZimaOS <= 1.5.0.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

ZimaOS is a fork of CasaOS, an operating system for Zima devices and x86-64 systems with UEFI

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.

IceWhaleTech Affected
ZimaOS
<= 1.5.0
Published
08 Jan 2026
Exploitation Reported
10 Apr 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

nuclei_scanner

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

The Shadowserver

Recorded 10 Apr 2026

A trusted third party reported exploitation.

Proof of concept available

Nuclei Templates

Recorded 12 Jun 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
The Shadowserver First 2026-04-10 00:00 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-21891.yaml 01 Jun 2026

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

9.4 Critical

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

2.3%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Improper Authentication CWE-287

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

ZimaOS - Authentication Bypass

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 14:21 UTC

    Public PoC available

    Public proof-of-concept code published

  2. 15:34 UTC

    Nuclei template available

    Scanner coverage available

  3. 00:00 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  4. 14:00 UTC

    CVE published

    Vulnerability disclosed publicly

  5. 17:24 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

Start 14-day Pro trial Read API docs
  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-21891

Sample API response 
{
  "cve_id": "CVE-2026-21891",
  "confidence": "High",
  "cvss_score": 9.4,
  "cvss_estimated": false,
  "epss_score": 0.02316,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}