Drop All Capabilities

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: drop-all-capabilities
  annotations:
    policies.kyverno.io/title: Drop All Capabilities
    policies.kyverno.io/category: Best Practices
    policies.kyverno.io/severity: medium
    policies.kyverno.io/minversion: 1.6.0
    policies.kyverno.io/subject: Pod
    policies.kyverno.io/description: "Capabilities permit privileged actions without giving full root access. All capabilities should be dropped from a Pod, with only those required added back. This policy ensures that all containers explicitly specify the `drop: [\"ALL\"]` ability. Note that this policy also illustrates how to cover drop entries in any case although this may not strictly conform to the Pod Security Standards."
spec:
  validationFailureAction: Audit
  background: true
  rules:
    - name: require-drop-all
      match:
        any:
          - resources:
              kinds:
                - Pod
      preconditions:
        all:
          - key: "{{ request.operation || 'BACKGROUND' }}"
            operator: NotEquals
            value: DELETE
      validate:
        message: Containers must drop `ALL` capabilities.
        foreach:
          - list: request.object.spec.[ephemeralContainers, initContainers, containers][]
            deny:
              conditions:
                all:
                  - key: ALL
                    operator: AnyNotIn
                    value: "{{ element.securityContext.capabilities.drop[].to_upper(@) || `[]` }}"