All the pods in a cluster are essentially able to communicate with each other, with the nodes in their own cluster, and with any other IT systems. If this communication is not restricted, malware or an attacker can exploit this to attack the control plane, other pods, or the nodes, for example.

There is also a risk that pods in the cluster will be unintentionally accessible from the outside. This would allow an external attack against services that should only be accessible within the cluster. This threat is exacerbated by the fact that less attention is often paid to internal services. If a vulnerability is tolerated in a service that is only used internally but is also accessible from the outside, this puts the entire cluster at considerable risk.