Single Sign OnApplication · Redhat
CVE-2021-3424
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 · uneditedA flaw was found in keycloak as shipped in Red Hat Single Sign-On 7.4 where IDN homograph attacks are possible. A malicious user can register himself with a name already registered and trick admin to grant him extra privileges.
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 · moderate confidenceKeycloak 7.4 does not properly validate Internationalized Domain Names (IDN) during user registration, allowing homograph attacks where malicious users can register usernames visually identical to existing users using confusable Unicode characters (e.g., Cyrillic vs Latin letters). This enables privilege escalation by tricking administrators into granting additional access to the wrong account.
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
Single Sign OnApplication
= 7.4CVSS 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
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
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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Identify the Keycloak or RH SSO versionCheck the server version through the admin console, server logs, or by querying the /auth/realms/{realm} endpoint. On RH SSO, also check rpm -q or the installation manifest.Affected if The installed version is Red Hat Single Sign-On 7.4 exactly
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Confirm user registration is enabledLog into the admin console, navigate to Authentication > Flows, and verify the 'Registration' flow is active. Alternatively, check the realm settings under Authentication > Required Actions to see if 'Register' is enabled for users.Affected if User self-registration is enabled and accessible to unauthenticated users
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Verify IDN homograph protection is configuredCheck the realm configuration for username validator settings. Inspect the 'Regex Pattern' validator applied to the username attribute in user registration or in the user storage configuration. Look for patterns that restrict or reject non-ASCII/confusable Unicode characters.Affected if No regex validator or homograph protection is configured to filter confusable Unicode characters like Cyrillic lookalikes
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Test for vulnerable IDN character acceptanceAttempt a test registration using a username containing confusable Unicode characters (for example, Cyrillic letters that visually match Latin letters in your admin account). Submit the registration form and observe whether it succeeds.Affected if The system accepts usernames with Unicode characters that are confusable with existing usernames
A user is affected if running RH SSO 7.4 with user registration enabled and without IDN homograph protection configured to reject confusable Unicode characters in usernames.
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 dataImplement IDN homograph protection by restricting confusable Unicode characters in usernames, enabling punycode representation for display, or implementing visual similarity detection to reject lookalike usernames during registration.
Fix this in Single Sign On
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-3424 — 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-2021-3424 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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- Version or environment caveats, and links to real fixes
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