CVE-2023-6717 is a Cross-Site Scripting (XSS) vulnerability identified in the SAML client registration component of Keycloak, an open-source identity and access management solution widely used for single sign-on and identity federation. The flaw arises from improper neutralization of input during web page generation, specifically allowing an administrator or a client with registration privileges to register malicious JavaScript URIs as Assertion Consumer Service POST Binding URLs (ACS). These URLs are critical endpoints in the SAML authentication flow where assertions are posted back to the service provider. By injecting malicious JavaScript into these URLs, an attacker can execute arbitrary scripts in the context of users interacting with different realms or applications managed by the same Keycloak instance. This cross-realm impact means that a compromised or malicious admin in one realm can target users in other realms, potentially bypassing typical isolation boundaries. The exploitation requires high privileges (administrator or client with registration access) and user interaction (form submission), but once triggered, it can lead to unauthorized access, session hijacking, data theft, or manipulation of the Keycloak instance’s confidentiality, integrity, and availability. The vulnerability affects Keycloak versions up to and including 24.0.0. Although no known exploits are reported in the wild yet, the medium CVSS score of 6.0 reflects the significant risk posed by this vulnerability, especially in environments where multiple realms and clients coexist and where administrative access is shared or delegated.

For European organizations, the impact of CVE-2023-6717 can be substantial, particularly for enterprises and public sector entities relying on Keycloak for centralized identity management across multiple applications and user groups. Exploitation could lead to unauthorized access to sensitive personal data protected under GDPR, resulting in regulatory penalties and reputational damage. The cross-realm nature of the vulnerability increases the risk of lateral attacks within an organization’s identity infrastructure, potentially compromising multiple business units or subsidiaries. Additionally, the ability to execute arbitrary JavaScript could facilitate further attacks such as credential theft, session hijacking, or injection of malicious payloads into trusted applications. This undermines trust in the authentication system and could disrupt critical services, impacting availability. Given the widespread adoption of Keycloak in European government, healthcare, finance, and large enterprises, the vulnerability poses a risk to confidentiality, integrity, and availability of identity services and downstream applications.

To mitigate CVE-2023-6717, European organizations should: 1) Immediately upgrade Keycloak to a version where this vulnerability is patched once available, or apply any vendor-provided patches or workarounds. 2) Restrict administrative and client registration privileges strictly to trusted personnel and systems, enforcing the principle of least privilege to minimize the risk of malicious registrations. 3) Implement rigorous input validation and sanitization on all user-supplied URLs and parameters within Keycloak configurations, especially for ACS URLs. 4) Monitor Keycloak logs and audit trails for unusual client registrations or changes to SAML configurations that could indicate exploitation attempts. 5) Employ Content Security Policy (CSP) headers and other browser security mechanisms to limit the impact of potential XSS payloads. 6) Conduct regular security assessments and penetration testing focused on identity management components to detect similar vulnerabilities. 7) Educate administrators on the risks of registering untrusted URLs and the importance of secure configuration management. These steps go beyond generic advice by focusing on administrative controls, configuration hygiene, and proactive monitoring specific to the nature of this vulnerability.