Restrict Binding System Groups

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: restrict-binding-system-groups
  annotations:
    policies.kyverno.io/title: Restrict Binding System Groups
    policies.kyverno.io/category: Security, EKS Best Practices
    policies.kyverno.io/severity: medium
    policies.kyverno.io/subject: RoleBinding, ClusterRoleBinding, RBAC
    kyverno.io/kyverno-version: 1.8.0
    policies.kyverno.io/minversion: 1.6.0
    kyverno.io/kubernetes-version: "1.23"
    policies.kyverno.io/description: Certain system groups exist in Kubernetes which grant permissions that are used for certain system-level functions yet typically never appropriate for other users. This policy prevents creating bindings to some of these groups including system:anonymous, system:unauthenticated, and system:masters.
spec:
  validationFailureAction: Audit
  background: true
  rules:
    - name: restrict-anonymous
      match:
        any:
          - resources:
              kinds:
                - RoleBinding
                - ClusterRoleBinding
      validate:
        message: Binding to system:anonymous is not allowed.
        pattern:
          subjects:
            - name: "!system:anonymous"
    - name: restrict-unauthenticated
      match:
        any:
          - resources:
              kinds:
                - RoleBinding
                - ClusterRoleBinding
      validate:
        message: Binding to system:unauthenticated is not allowed.
        pattern:
          subjects:
            - name: "!system:unauthenticated"
    - name: restrict-masters
      match:
        any:
          - resources:
              kinds:
                - RoleBinding
                - ClusterRoleBinding
      validate:
        message: Binding to system:masters is not allowed.
        pattern:
          subjects:
            - name: "!system:masters"