Critical Red Hat Kubernetes SSRF Flaw Exposes Internal Services
A critical Server-Side Request Forgery (SSRF) vulnerability in Red Hat's Multicluster Engine for Kubernetes allows unauthenticated attackers to access internal services across managed clusters.
Red Hat has disclosed CVE-2026-66794, a critical Server-Side Request Forgery (SSRF) vulnerability affecting the cluster-proxy-addon component within its Multicluster Engine for Kubernetes. This flaw, rated with a CVSS v3.1 score of 9.3, poses a significant risk by enabling unauthenticated remote attackers to reach internal services that would normally be inaccessible across managed Kubernetes clusters.
The vulnerability resides in a user-facing route exposed by the cluster proxy add-on. Red Hat's analysis indicates that this route lacks proper authentication and authorization enforcement before forwarding requests. Consequently, an attacker who can access this endpoint can manipulate URL path segments to trick the proxy into sending requests to arbitrary services within managed clusters. This mechanism is a classic example of SSRF (CWE-918), where an attacker abuses a vulnerable proxy as an intermediary rather than directly attacking an internal service from the internet.
In a multicluster Kubernetes environment, the implications of this SSRF vulnerability are particularly severe. Management-plane components often maintain connectivity to services distributed across multiple managed clusters. When exposed through a vulnerable route, these connections can be exploited by attackers to bypass network controls, service exposure restrictions, or cluster segmentation policies that are designed to protect sensitive internal resources.
Attackers could leverage this flaw to access internal APIs, retrieve sensitive application data, identify reachable internal endpoints, or interact with services that were never intended to be exposed externally. For instance, an attacker could craft a request that causes the affected proxy to contact an internal service within a managed cluster. If this internal service responds with configuration data, authentication tokens, debugging details, or application responses without requiring separate authentication, the attacker could gain valuable information to facilitate further intrusion.
While the CVSS score is a critical 9.3, Red Hat has classified the issue as 'Important' rather than 'Critical' in its advisory. This distinction is based on Red Hat's assessment that the confirmed impact is SSRF, not remote code execution. The vendor's analysis indicates a high confidentiality impact, a low integrity impact, and no demonstrated availability impact. The specific affected components are identified as multicluster-engine/cluster-proxy-addon-rhel9 and multicluster-engine/cluster-proxy-rhel9 within the Multicluster Engine for Kubernetes.
As of the publication of this advisory, Red Hat has listed both components as affected and has not yet identified associated security errata. Organizations utilizing Red Hat's Multicluster Engine for Kubernetes are strongly advised to take immediate action to mitigate this risk. The primary recommendation is to restrict network access to the user-facing cluster-proxy-addon route.
Red Hat suggests implementing firewall rules or equivalent network controls to ensure that only trusted networks and authorized sources can connect to the exposed port. Furthermore, administrators should conduct a thorough review of their route exposure configurations, inspect proxy access logs for any unusual path patterns or suspicious requests, and identify any sensitive internal services that are reachable from the management environment. Proactive monitoring and access control are crucial to prevent exploitation of this critical SSRF vulnerability.