CVE-2023-6134 is a cross-site scripting vulnerability identified in the Red Hat build of Keycloak 22, an open-source identity and access management solution widely used for authentication and authorization. The vulnerability stems from an incomplete remediation of a prior issue (CVE-2020-10748) related to improper input neutralization during web page generation. Specifically, Keycloak's mechanism to prevent unsafe redirect schemes is flawed because it permits certain schemes if a wildcard character is appended to the token. This loophole allows an attacker to craft specially designed requests that bypass the intended validation and inject malicious scripts into web pages served by Keycloak. When a victim user interacts with such a crafted URL, the malicious script executes in their browser context, potentially compromising session tokens, stealing sensitive information, or enabling further attacks such as phishing or privilege escalation. The CVSS 3.1 base score is 4.6 (medium severity), reflecting that the attack vector is network-based with low complexity but requires privileges and user interaction. The impact primarily affects confidentiality and integrity, with no direct availability impact. No public exploits have been reported yet, but the vulnerability's presence in a critical authentication component makes it a significant concern. The flaw highlights the importance of thorough validation of redirect URIs and input sanitization in authentication flows to prevent XSS attacks.

For European organizations, the exploitation of CVE-2023-6134 could lead to unauthorized disclosure of sensitive authentication tokens and user data, undermining trust in identity management systems. This can facilitate session hijacking, unauthorized access to protected resources, and lateral movement within networks. Sectors such as finance, government, healthcare, and critical infrastructure that rely heavily on Keycloak for secure authentication are at heightened risk. The confidentiality breach could result in regulatory non-compliance under GDPR, leading to legal and financial penalties. Although the vulnerability does not directly impact system availability, the resulting compromise of user credentials or sessions can cause operational disruptions and reputational damage. The requirement for user interaction and privileges somewhat limits the attack scope but does not eliminate risk, especially in environments with many users and complex access hierarchies.

European organizations should immediately monitor for updates and patches from Red Hat addressing CVE-2023-6134 and apply them promptly once available. In the interim, administrators should audit and restrict allowed redirect URIs to a strict whitelist, avoiding wildcards or ambiguous schemes that could be exploited. Implementing robust Content Security Policies (CSP) can help mitigate the impact of injected scripts by restricting script execution sources. Additionally, organizations should review and enhance input validation and sanitization mechanisms within their Keycloak deployments. Logging and monitoring for unusual redirect requests or suspicious user activity can aid in early detection of exploitation attempts. Educating users about the risks of clicking on unsolicited or suspicious links related to authentication flows can reduce the likelihood of successful attacks. Finally, consider deploying web application firewalls (WAF) with rules tailored to detect and block XSS payloads targeting Keycloak endpoints.