A hub cluster is the central management cluster in Red Hat Advanced Cluster Management for Kubernetes (RHACM). It hosts the control-plane components that coordinate policies, subscriptions, monitoring, and lifecycle actions across multiple managed clusters. In other words, it is the place where cluster-wide decisions are made and enforced.
This matters because the hub cluster concentrates trust and authority. If an attacker gains access to hub-cluster management paths, they may be able to influence many connected clusters, not just one workload namespace. In practice, hub-cluster components often run controllers and service accounts with broad permissions, so authorization bugs or misconfigurations can become privilege-escalation paths. Defenders treat the hub as a high-value target: harden RBAC, minimize controller privileges, protect secrets, and monitor management-plane activity closely.