CVE-2023-6544 in Keycloak
Summary
by MITRE • 04/25/2024
A flaw was found in the Keycloak package. This issue occurs due to a permissive regular expression hardcoded for filtering which allows hosts to register a dynamic client. A malicious user with enough information about the environment could jeopardize an environment with this specific Dynamic Client Registration and TrustedDomain configuration previously unauthorized.
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Analysis
by VulDB Data Team • 11/11/2025
The vulnerability identified as CVE-2023-6544 resides within the Keycloak identity and access management platform, specifically affecting the Dynamic Client Registration feature. This flaw represents a critical security weakness that undermines the integrity of the authentication and authorization mechanisms. The vulnerability stems from a hardcoded permissive regular expression that governs host filtering during dynamic client registration processes. Such a configuration allows unauthorized entities to register clients with hostnames that should normally be restricted or blocked, effectively bypassing security controls that were designed to prevent malicious registration attempts.
The technical implementation of this vulnerability involves a hardcoded regular expression pattern that fails to properly validate incoming hostnames during the dynamic client registration workflow. This permissive pattern enables attackers to register clients with arbitrary hostnames that would typically be rejected by stricter validation rules. When combined with TrustedDomain configurations, this weakness creates a pathway for malicious actors to establish unauthorized client registrations that can then be leveraged for further attacks. The vulnerability specifically impacts environments where dynamic client registration is enabled alongside trusted domain policies, creating a scenario where the security boundaries established by domain restrictions become ineffective.
The operational impact of CVE-2023-6544 extends beyond simple privilege escalation, potentially enabling sophisticated attack vectors that can compromise entire authentication ecosystems. An attacker exploiting this vulnerability could register malicious clients with trusted domains, potentially leading to unauthorized access to protected resources, data exfiltration, or the establishment of persistent access points within the environment. The attack surface is particularly concerning in multi-tenant environments or scenarios where Keycloak serves as a central identity provider, as successful exploitation could allow attackers to compromise the authentication infrastructure itself. This vulnerability directly relates to CWE-20 Improper Input Validation, which encompasses issues where input validation is insufficient or improperly implemented, and can be mapped to ATT&CK technique T1566.002 Phishing via Service Provider, as it enables the creation of malicious client registrations that could be used in social engineering campaigns.
Organizations affected by this vulnerability should immediately implement mitigations including updating to patched versions of Keycloak, reviewing and strengthening domain validation rules, and monitoring for unauthorized client registrations. Security teams should also consider implementing additional controls such as rate limiting for client registration requests, enhanced logging of registration activities, and periodic audits of registered clients to identify potential malicious entries. The vulnerability highlights the critical importance of proper input validation and the dangers of hardcoded security parameters that can be easily bypassed by determined attackers. Organizations should conduct thorough assessments of their Keycloak implementations to identify configurations that may be vulnerable to similar issues and establish robust monitoring procedures to detect anomalous client registration patterns that could indicate exploitation attempts.