CVE-2023-6134 is a cross-site scripting (XSS) vulnerability identified in the Red Hat build of Keycloak version 22. Keycloak is an open-source identity and access management solution widely used for single sign-on and authentication services. The vulnerability stems from improper neutralization of input during web page generation, specifically in the handling of redirect schemes. While Keycloak attempts to restrict certain redirect schemes to prevent malicious redirects, this flaw allows an attacker to bypass these restrictions by appending a wildcard character to the token, effectively circumventing the validation logic. This incomplete fix is a regression or partial resolution of a prior vulnerability (CVE-2020-10748). An attacker with at least some level of authenticated access can craft a specially designed request that triggers the XSS vulnerability, potentially injecting malicious scripts into the victim's browser context. The CVSS 3.1 base score of 4.6 reflects that the attack vector is network-based, requires low attack complexity, privileges, and user interaction, and impacts confidentiality and integrity to a limited extent without affecting availability. No public exploits or widespread attacks have been reported to date. The vulnerability highlights the importance of robust input validation and output encoding in web applications, especially in identity management platforms that handle sensitive authentication flows.

For European organizations, the exploitation of CVE-2023-6134 could lead to unauthorized script execution within the context of authenticated users, potentially enabling session hijacking, credential theft, or further exploitation of user privileges. Although the confidentiality and integrity impacts are limited, the vulnerability undermines trust in the authentication process and could facilitate lateral movement or privilege escalation in complex environments. Organizations relying on Keycloak 22 for critical identity and access management services may face risks to user data privacy and security compliance, particularly under GDPR regulations. The absence of known exploits reduces immediate risk, but the presence of an incomplete fix suggests that attackers may develop exploits if the vulnerability is not addressed. The vulnerability does not affect availability directly but could indirectly impact service reliability if exploited at scale. Given Keycloak’s role in federated identity and single sign-on, exploitation could have cascading effects across multiple connected applications and services within European enterprises.

European organizations should immediately verify if they are running Red Hat build of Keycloak version 22 and prioritize upgrading to a patched version once available from Red Hat. In the interim, administrators should audit and restrict redirect URIs and schemes to trusted domains only, avoiding wildcard usage in tokens or redirect parameters. Implement strict Content Security Policy (CSP) headers to limit the impact of potential XSS payloads. Conduct thorough input validation and output encoding on all user-controllable inputs related to redirects and tokens. Monitor authentication logs for unusual redirect patterns or suspicious user activity indicative of attempted exploitation. Educate users about phishing and social engineering risks that could leverage this vulnerability. Engage with Red Hat support for any available backported patches or workarounds. Finally, integrate vulnerability scanning and penetration testing focused on authentication flows to detect similar issues proactively.