The vulnerability arises from the cluster-proxy service-proxy component appending impersonation group headers to proxied requests without removing caller-supplied values first. Because the spoke ServiceAccount has unrestricted impersonation permissions, an authenticated hub principal can inject an Impersonate-Group header to escalate privileges to cluster-admin on all managed clusters. This is classified as a Confused Deputy vulnerability (CWE-441). The CVSS 3.1 base score is 8.5, reflecting network attack vector, high impact on confidentiality, integrity, and availability, and requiring low privileges but high attack complexity. Red Hat published security advisories (RHSA-2026:46885 and RHSA-2026:47388) confirming the issue and releasing updated multicluster engine for Kubernetes images at version 2.10.4 that include security fixes.

An authenticated hub principal can exploit this vulnerability to escalate privileges to cluster-admin on every managed Kubernetes cluster under the multicluster engine management. This could lead to full control over the clusters, impacting confidentiality, integrity, and availability of the managed environments.

Red Hat has released updated multicluster engine for Kubernetes images in version 2.10.4 that address this vulnerability. Users should upgrade to version 2.10.4 or later to remediate the issue. Refer to Red Hat's official documentation for installation and upgrade instructions: https://access.redhat.com/documentation/en-us/red_hat_advanced_cluster_management_for_kubernetes/2.15/html/clusters/cluster_mce_overview#mce-install-intro. No temporary or alternative mitigations are indicated in the advisory.