CVE-2025-3501 is a vulnerability identified in Red Hat Build of Keycloak, an open-source identity and access management solution widely used for authentication and authorization. The vulnerability is triggered when the verification policy is configured to 'ALL'. Under this setting, the system unintentionally skips the verification of certificates in the trust store, specifically failing to validate that the certificate's hostname matches the expected host. This improper validation flaw allows an attacker to present a certificate with a mismatched hostname and still have it accepted as valid by the Keycloak server. The vulnerability does not require any privileges or user interaction to exploit, and it can be remotely triggered over the network. The CVSS v3.1 score of 8.2 reflects a high severity due to the potential for confidentiality compromise, as attackers could impersonate legitimate services or intercept sensitive authentication tokens. The integrity impact is rated low, and availability is unaffected. No known exploits have been reported yet, but the flaw presents a significant risk in environments where secure certificate validation is critical. The affected versions are 25.0.0, 26.0.0, and 26.2.0 of Red Hat Build of Keycloak. The vulnerability was published on April 29, 2025, and has been enriched by CISA, indicating recognition by US cybersecurity authorities.

For European organizations, the impact of CVE-2025-3501 can be substantial, especially for those relying on Keycloak for identity federation, single sign-on, and secure authentication services. The improper certificate validation can enable man-in-the-middle (MITM) attacks, allowing adversaries to intercept or manipulate authentication tokens and sensitive data, leading to unauthorized access to internal systems and services. Confidentiality breaches could expose user credentials and personal data, potentially violating GDPR and other data protection regulations. The flaw could also undermine trust in federated identity systems, affecting business continuity and user confidence. Organizations in sectors such as finance, healthcare, government, and critical infrastructure are particularly vulnerable due to the sensitive nature of their data and regulatory requirements. The lack of required authentication or user interaction for exploitation increases the risk of automated or widespread attacks. Although availability is not directly impacted, the indirect consequences of compromised authentication could lead to service disruptions or escalated attacks.

To mitigate CVE-2025-3501, European organizations should immediately review their Keycloak configurations, specifically the certificate verification policies. Avoid setting the verification policy to 'ALL' until a patch or official fix is applied. Instead, use stricter verification settings that enforce hostname validation and trust store checks. Monitor Keycloak vendor advisories and apply patches promptly once available. Implement network-level protections such as TLS interception detection and anomaly-based intrusion detection systems to identify suspicious certificate usage. Conduct regular audits of authentication logs to detect unusual access patterns that may indicate exploitation attempts. Employ certificate pinning where feasible to reduce reliance on trust stores. Additionally, organizations should educate administrators on secure certificate management and enforce multi-factor authentication to reduce the impact of compromised credentials. Finally, consider isolating Keycloak instances and limiting their network exposure to reduce attack surface.