Home/CVE/ZimaOS is a fork of CasaOS, an operating system for Zima devices and x86-64 systems with UEFI. In versions up to and inc
CVE
CVE-2026-21891
ZimaOS is a fork of CasaOS, an operating system for Zima devices and x86-64 systems with UEFI. In versions up to and inc
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.
CRITICAL · CVSS 9.4
EPSS 0.06362
Act now
- EPSS percentile: top 9% of all CVEs by exploitation likelihood
- Public exploit or PoC is available
- SSVC automatable: yes - attacks can be scripted at scale
- CVSS base score ≥ 7.0
Sigma rules0
YARA rules0
Look this up elsewhere - one-click external pivots
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How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2026-21891, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.
Triage: should I act now? Four signals, and they are not interchangeable:
CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked.
EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal.
CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score.
Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.
How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.
Then what - two workflows:
Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits.
PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.
Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).
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ATT&CK techniques
8Techniques this CVE enables - linked via CWECAPECATT&CK. High◆ = named directly in ATT&CK or Nuclei templates.
T1040 · Network Sniffing T1134 · Access Token Manipulation T1185 · Browser Session Hijacking T1505.003 · Web Shell T1548 · Abuse Elevation Control Mechanism T1550.001 · Application Access Token T1557 · Adversary-in-the-Middle T1563 · Remote Service Session Hijacking
▤ Build a SIEM detection for these techniques
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CAPEC attack patterns
10Attack patterns this CVE enables - the bridge from weakness to ATT&CK technique.
CAPEC-CAPEC-114 · Authentication Abuse CAPEC-CAPEC-115 · Authentication Bypass CAPEC-CAPEC-151 · Identity Spoofing CAPEC-CAPEC-194 · Fake the Source of Data CAPEC-CAPEC-22 · Exploiting Trust in Client CAPEC-CAPEC-57 · Utilizing REST's Trust in the System Resource to Obtain Sensitive Data CAPEC-CAPEC-593 · Session Hijacking CAPEC-CAPEC-633 · Token Impersonation CAPEC-CAPEC-650 · Upload a Web Shell to a Web Server CAPEC-CAPEC-94 · Adversary in the Middle (AiTM)
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Weakness Classification
CWE-287Improper Authentication
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Affected Products & Versions
1zimaspace zimaos<= 1.5.0
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Public Exploits & PoCs
4These PoC and exploit links come from public sources and are not verified to be safe or functional. Review the code before running anything, and treat unverified entries as untrusted.
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Scoring & Timeline
9.4
CRITICAL · CVSS v3.1 · [email protected]
Attack Vector
Network
Adjacent
Local
Physical
Attack Complexity
Low
High
Privileges Required
None
Low
High
User Interaction
None
Required
Scope
Unchanged
Changed
Confidentiality
None
Low
High
Integrity
None
Low
High
Availability
None
Low
High
SSVC triage · cisa-vulnrichment
Exploitation
poc
Automatable
yes
Technical impact
total
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.