cenroq · securing your clusters.

Rejects unless

!has(object.rules) || object.rules.all(r,
  !(has(r.verbs) && has(r.resources) &&
    r.verbs.exists(v, v == "impersonate" || v == "*") &&
    r.resources.exists(res, variables.impersonateResources.exists(ir, ir == res))
  )
)

ClusterRoles must not grant the impersonate verb on users, groups or serviceaccounts.

Variables

impersonateResources

["users","groups","serviceaccounts","uids","userextras","*"]

Remediation

Remove the impersonate verb, and any wildcard verb, from every rule covering users, groups, serviceaccounts, uids or userextras. Fields: rules[*].resources, rules[*].verbs.

Applies to

clusterroles · rbac.authorization.k8s.io/v1 · CREATE, UPDATE

Manifest

apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingAdmissionPolicy
metadata:
  name: clusterrole-rbac-impersonate
  annotations:
    kubeapt.io/uuid: "e0406702-6119-41cd-9ee8-978e1f3b9689"
    security.kubeapt.io/displayName: "Grants the impersonate Verb"
    security.kubeapt.io/description: "Impersonation lets the holder send requests as any other user, group or service account, borrowing the permissions of cluster-admin identities without ever being granted those permissions in its own bindings."
    security.kubeapt.io/resource: "ClusterRoles"
    security.kubeapt.io/severity: "Critical"
    security.kubeapt.io/remediation: "Remove the impersonate verb, and any wildcard verb, from every rule covering users, groups, serviceaccounts, uids or userextras. Fields: rules[*].resources, rules[*].verbs."
    security.kubeapt.io/product: "Kubernetes"
spec:
  failurePolicy: Fail
  matchConstraints:
    resourceRules:
    - apiGroups:
      - rbac.authorization.k8s.io
      apiVersions:
      - v1
      operations:
      - CREATE
      - UPDATE
      resources:
      - clusterroles
  variables:
  - name: impersonateResources
    expression: |
      ["users","groups","serviceaccounts","uids","userextras","*"]
  validations:
  - expression: |
      !has(object.rules) || object.rules.all(r,
        !(has(r.verbs) && has(r.resources) &&
          r.verbs.exists(v, v == "impersonate" || v == "*") &&
          r.resources.exists(res, variables.impersonateResources.exists(ir, ir == res))
        )
      )
    message: |
      ClusterRoles must not grant the impersonate verb on users, groups or serviceaccounts.

Save it as clusterrole-rbac-impersonate.yaml — the commands below assume that name.

Validate with kubeapt

Check a workload against this one policy, before anything is installed on a cluster.

$ kubeapt validate -p ./clusterrole-rbac-impersonate.yaml -r ./workload.yaml

Or without the file, from the published policy set — -r takes a directory too:

$ kubeapt policies download && kubeapt validate --policy-name clusterrole-rbac-impersonate -r ./manifests

Or against every namespace in the cluster your kubeconfig points at:

$ kubeapt validate --policy-name clusterrole-rbac-impersonate -A

Bundles

cenroq-best-practices

Source

View policy.yaml on GitHub →