CVE-2025-11419 is a vulnerability identified in Keycloak, an open-source identity and access management solution widely used for authentication and authorization services. The flaw arises from the lack of limits or throttling on TLS 1.2 client-initiated renegotiation requests. An unauthenticated remote attacker can exploit this by repeatedly initiating TLS renegotiations, which are computationally expensive operations for the server. This leads to excessive CPU consumption, effectively causing a denial of service (DoS) by exhausting server resources and rendering the Keycloak service unavailable. The vulnerability affects multiple versions of Keycloak, including 0, 26.2.0, and 26.4.0. Since no authentication or user interaction is required, the attack surface is broad, and exploitation can be automated. The CVSS v3.1 base score of 7.5 classifies this as a high-severity issue, primarily impacting availability (A:H) with no confidentiality or integrity impact. Although no known exploits are currently reported in the wild, the nature of the vulnerability makes it a significant risk for organizations relying on Keycloak for critical authentication services. The absence of patch links suggests that fixes may be forthcoming or that mitigations need to be applied at the network or configuration level. The vulnerability was reserved in October 2025 and published in December 2025, indicating recent discovery and disclosure.

For European organizations, the impact of CVE-2025-11419 can be substantial, especially for those that depend on Keycloak for identity and access management across internal and customer-facing applications. A successful DoS attack can disrupt authentication services, leading to denial of access for legitimate users, interruption of business processes, and potential cascading effects on other dependent systems. This can affect sectors such as finance, healthcare, government, and critical infrastructure where continuous authentication availability is essential. The attack requires no credentials or user interaction, increasing the risk of widespread exploitation. Additionally, service outages may lead to compliance issues under regulations like GDPR if they affect data access or processing. The inability to authenticate users can also hinder incident response and security monitoring activities, increasing overall organizational risk.

To mitigate CVE-2025-11419, organizations should implement specific controls beyond generic advice: 1) Deploy rate limiting or throttling mechanisms on TLS renegotiation requests at the network perimeter or load balancer to prevent excessive renegotiation attempts. 2) Configure Keycloak or underlying TLS libraries to disable or restrict client-initiated TLS renegotiation if possible. 3) Monitor server CPU utilization and network traffic patterns for unusual spikes indicative of renegotiation abuse. 4) Apply any official patches or updates from Keycloak or Red Hat as soon as they become available. 5) Use Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with signatures or heuristics to detect and block renegotiation-based DoS attempts. 6) Consider deploying redundant Keycloak instances with load balancing to improve resilience against resource exhaustion. 7) Maintain incident response plans that include procedures for DoS attacks targeting authentication infrastructure.