Keycloak Wildcard Domain Validation Bypass in Keycloak-services

Executive Summary

This vulnerability is in Keycloak's keycloak-services component. It involves improper validation of wildcard domains used by realm administrators to restrict client registration or updates. Attackers can bypass these restrictions by controlling reverse DNS, allowing unauthorized client modifications even if they don't own a legitimate subdomain.

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Detection Guidance

To detect this vulnerability, inspect Keycloak's client policy configurations for wildcard domain restrictions (e.g., *.example.com). Check if the hostname matching logic improperly validates subdomains by verifying if it only checks suffixes without proper boundary validation. Review logs for unauthorized client registration or update attempts from unexpected hosts.

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Impact Analysis

If you are a Keycloak administrator using wildcard domains for client restrictions, attackers could exploit this to modify clients without proper authorization. This may lead to unauthorized access to services or data managed by Keycloak, depending on the compromised client's permissions.

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Compliance Impact

This vulnerability could undermine compliance efforts by allowing unauthorized access to sensitive data or systems. For GDPR, it may violate principles of data protection and access control. For HIPAA, it could lead to unauthorized access to protected health information, potentially breaching confidentiality requirements.

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Mitigation Strategies

Avoid using wildcard domains (like *.example.com) for host-based restrictions in Keycloak realm administrator settings. Replace them with explicit domain lists to prevent unauthorized client modifications.

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