CVE-2026-21891
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedZimaOS 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceZimaOS versions up to 1.5.0 contain an authentication bypass where password validation is skipped or incorrectly handled for known system service accounts. When a user provides a username matching a system service account, the login function grants authenticated access regardless of the password supplied, effectively allowing anyone with knowledge of these usernames to access the system.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 1.5.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed ZimaOS versionLocate the ZimaOS version information in the system settings, About page, or by running the command 'zimaos-version' or 'cat /etc/zimaos-release' if accessible via CLIAffected if The version is 1.5.0 or lower (no patch version specified, treat any version up to and including 1.5.0 as affected)
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Identify system service accountsReview the user management panel, user database, or configuration files that define system accounts. Look for usernames that appear to be built-in service accounts (commonly named after system services like admin, backup, sync, system, or service-related terms)Affected if Any system service accounts exist in the user directory (the vulnerability specifically affects known system service account usernames)
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Verify if service accounts are enabledCheck the account status in user management - look for whether these service accounts are marked as active, enabled, or have login privilegesAffected if System service accounts are active and have login permission enabled
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Review authentication configurationExamine the authentication configuration files or login module settings. Look for any code or settings that handle password validation differently based on username typeAffected if Authentication logic conditionally skips or weakens password validation for certain usernames
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Check for unauthorized access indicatorsReview access logs, authentication logs, or security event logs for login attempts using service account usernames that succeeded with incorrect passwords or from unexpected source IPsAffected if Any successful logins to service accounts occurred with incorrect passwords or from unauthorized sources
You are affected if running ZimaOS version 1.5.0 or lower and the system contains active service account usernames that could bypass password validation.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataSince no patch is available, implement network-level access controls to restrict login interface exposure, identify and disable or rename vulnerable service accounts, and monitor for unauthorized access attempts until an official patch is released.
- Consultation8.0 h
- Implementation16.0 h
- Testing12.0 h
- Review / QA6.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $11,776.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-21891 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-21891 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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