Authentication Bypass via Untrusted Headers in Keycloak

Executive Summary

This vulnerability affects Keycloak's Conditional OTP authenticator. It allows an attacker with a user's password to bypass two-factor authentication by sending a specially crafted HTTP header. The system fails to verify if the header comes from a trusted source before skipping OTP verification.

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Detection Guidance

To detect this vulnerability, inspect Keycloak server logs for login attempts where OTP was skipped without proper validation. Check for requests containing suspicious headers that match configured skip rules. Review Keycloak configuration files for Conditional OTP settings and proxy header configurations.

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Impact Analysis

If exploited, an attacker could gain unauthorized access to your account even with your password. They could then modify your data, perform administrative actions if you have elevated privileges, or access sensitive information. This requires the attacker to already know your password and the system to use a specific Conditional OTP configuration.

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Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating compliance requirements for data protection such as GDPR and HIPAA. It undermines multi-factor authentication, a key security measure required by these regulations to protect user data and privacy.

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Mitigation Strategies

Disable the Conditional OTP flow in Keycloak realms where it is configured with skip-header rules. Ensure no realms rely on proxy header-based OTP bypasses. Monitor for unusual login patterns or failed OTP attempts that may indicate exploitation attempts.

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