The vulnerability arises because the service-proxy component appends impersonation group headers to proxied requests without removing caller-supplied values first. Since 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 a confused deputy type flaw affecting Red Hat Advanced Cluster Management for Kubernetes and multicluster-engine. The CVSS v3.1 score is 8.5 (high severity) with network attack vector, high impact on confidentiality, integrity, and availability, and requiring low privileges but high attack complexity. Red Hat has published advisories (RHSA-2026:46885 and RHSA-2026:47388) for multicluster engine for Kubernetes 2.10, including updated container images and documentation for remediation.

An authenticated hub principal can escalate privileges to cluster-admin on every managed Kubernetes cluster by exploiting the improper handling of impersonation group headers in the service-proxy component. This could lead to full control over managed clusters, impacting confidentiality, integrity, and availability of cluster resources.

Red Hat has released updated multicluster engine for Kubernetes images in version 2.10.4 that address this vulnerability. Users should apply the security update by installing the updated images as per Red Hat's documentation at 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 other specific mitigations are indicated in the advisory. Patch status is confirmed by the vendor advisory.