CVE-2023-6544 is a vulnerability identified in Keycloak versions 22.0.0 and 23.0.0, stemming from a permissive regular expression hardcoded within the software's filtering mechanism for host validation during Dynamic Client Registration. Keycloak is an open-source identity and access management solution widely used for securing applications and services. The flaw allows malicious actors who have some level of authenticated access and knowledge about the environment to bypass intended restrictions on which hosts can register dynamic clients. This is possible because the regular expression used to filter allowed hosts is overly permissive, enabling unauthorized hosts to be accepted. Dynamic Client Registration is a feature that allows clients (applications) to register themselves dynamically with the authorization server, which is critical for flexible and scalable identity management. If an attacker successfully registers a rogue client, they could potentially gain unauthorized access to sensitive resources or manipulate identity tokens, thereby compromising confidentiality and integrity of the system. The vulnerability does not impact availability and does not require user interaction, but it does require some level of privilege (authenticated user). Currently, there are no known exploits in the wild, but the medium CVSS score of 5.4 reflects the moderate risk posed by this issue. The vulnerability was published on April 25, 2024, and assigned by Red Hat. Since no official patches are linked yet, organizations must rely on configuration hardening and monitoring until updates are released.

For European organizations, the impact of CVE-2023-6544 can be significant, especially for those relying on Keycloak for identity and access management in cloud environments, SaaS platforms, or internal applications. Unauthorized dynamic client registration can lead to unauthorized access to protected resources, data leakage, or privilege escalation within the identity management infrastructure. This could compromise sensitive personal data protected under GDPR, leading to regulatory and reputational damage. The vulnerability affects confidentiality and integrity but not availability, meaning systems remain operational but potentially compromised. Organizations in sectors such as finance, healthcare, government, and critical infrastructure, which often use Keycloak for secure authentication, are at higher risk. The ease of exploitation is moderate since it requires authenticated access and some environmental knowledge, but no user interaction is needed, making automated attacks feasible once the vulnerability is known. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as threat actors often develop exploits after public disclosure.

1. Monitor Keycloak dynamic client registrations closely for any unauthorized or suspicious activity, including unexpected new clients. 2. Review and tighten TrustedDomain configurations to restrict allowed hosts explicitly, avoiding overly permissive patterns or wildcards in regular expressions. 3. Limit authenticated user privileges to only those necessary for their roles to reduce the risk of exploitation by low-privilege users. 4. Implement network segmentation and access controls to restrict who can interact with the Keycloak server, minimizing exposure. 5. Stay updated with Keycloak vendor advisories and apply security patches promptly once released. 6. Conduct regular security audits and penetration testing focusing on identity management components. 7. Employ anomaly detection tools to identify unusual client registration patterns or authentication flows. 8. Educate administrators and developers about secure configuration practices for Dynamic Client Registration and TrustedDomain settings.