CVE-2025-2559 is a resource allocation vulnerability found in Red Hat Build of Keycloak, specifically when configured to use JWT tokens for authentication. Keycloak caches JWT tokens until their expiration to optimize authentication performance. However, if clients issue JWT tokens with excessively long expiration times (e.g., 24 to 48 hours), the cache can grow indefinitely because tokens remain stored until they expire. This unchecked cache growth consumes increasing amounts of memory, eventually triggering an OutOfMemoryError in the Java runtime environment. The resulting failure causes Keycloak to become unresponsive or crash, leading to a denial of service (DoS) condition that blocks legitimate users from authenticating. The vulnerability requires high privileges to exploit (e.g., the ability to configure or influence token issuance) but does not require user interaction. The flaw impacts availability but does not compromise confidentiality or integrity of data. No public exploits have been reported yet, and no patches are currently linked, indicating the need for proactive configuration management. This issue highlights the importance of setting reasonable JWT token expiration times and implementing resource usage limits or throttling mechanisms within authentication services to prevent resource exhaustion attacks.

For European organizations, this vulnerability poses a risk of service disruption in identity and access management systems relying on Keycloak, particularly those using JWT tokens with long expiration times. A successful exploitation could cause authentication services to become unavailable, impacting business operations, user productivity, and access to critical applications. Sectors such as finance, healthcare, government, and telecommunications, which often depend on robust authentication infrastructure, could experience significant operational impact. The denial of service could also affect compliance with regulations requiring continuous availability of authentication services. Since the vulnerability does not affect confidentiality or integrity, data breaches are unlikely, but service outages could lead to reputational damage and financial losses. Organizations with large user bases or high authentication traffic are more vulnerable due to the potential for rapid cache growth. The absence of known exploits provides a window for remediation, but the medium severity rating indicates that the threat should not be underestimated.

To mitigate CVE-2025-2559, European organizations should: 1) Configure JWT token expiration times to reasonable durations, avoiding excessively long lifetimes (e.g., limit tokens to a few hours rather than days). 2) Monitor Keycloak's memory usage and cache size metrics closely to detect abnormal growth early. 3) Implement resource limits or throttling on token issuance rates to prevent abuse or accidental overload. 4) Regularly update Keycloak to the latest versions where fixes or improvements may be released. 5) Review and restrict privileges related to token configuration and issuance to minimize risk of malicious or misconfigured long-lived tokens. 6) Consider deploying additional caching or token validation layers that can enforce expiration and cleanup policies more aggressively. 7) Conduct load testing to understand the impact of token expiration settings on resource consumption. 8) Prepare incident response plans for potential denial of service scenarios affecting authentication services. These steps go beyond generic advice by focusing on configuration tuning, monitoring, and privilege management specific to this vulnerability.