Restrict Binding System Groups

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: restrict-binding-system-groups
 5  annotations:
 6    policies.kyverno.io/title: Restrict Binding System Groups
 7    policies.kyverno.io/category: Security, EKS Best Practices
 8    policies.kyverno.io/severity: medium
 9    policies.kyverno.io/subject: RoleBinding, ClusterRoleBinding, RBAC
10    kyverno.io/kyverno-version: 1.8.0
11    policies.kyverno.io/minversion: 1.6.0
12    kyverno.io/kubernetes-version: "1.23"
13    policies.kyverno.io/description: >-
14      Certain system groups exist in Kubernetes which grant permissions that
15      are used for certain system-level functions yet typically never appropriate
16      for other users. This policy prevents creating bindings to some of these
17      groups including system:anonymous, system:unauthenticated, and system:masters.      
18spec:
19  validationFailureAction: audit
20  background: true
21  rules:
22    - name: restrict-anonymous
23      match:
24        any:
25        - resources:
26            kinds:
27              - RoleBinding
28              - ClusterRoleBinding
29      validate:
30        message: "Binding to system:anonymous is not allowed."
31        pattern:
32          subjects:
33            - name: "!system:anonymous"
34    - name: restrict-unauthenticated
35      match:
36        any:
37        - resources:
38            kinds:
39              - RoleBinding
40              - ClusterRoleBinding
41      validate:
42        message: "Binding to system:unauthenticated is not allowed."
43        pattern:
44          subjects:
45            - name: "!system:unauthenticated"
46    - name: restrict-masters
47      match:
48        any:
49        - resources:
50            kinds:
51              - RoleBinding
52              - ClusterRoleBinding
53      validate:
54        message: "Binding to system:masters is not allowed."
55        pattern:
56          subjects:
57            - name: "!system:masters"
58