cis-gke-v190-4-1-8

name	cis-gke-v190-4.1.8
description	Avoid bindings to system:anonymous (Automated)
category	cis-gke
version	1.9.0
author	cyberstrike-official
tags	["cis","gke","kubernetes","gcp","rbac","service-accounts","cluster-roles","secrets","wildcards"]
cis_id	4.1.8
cis_benchmark	CIS Google Kubernetes Engine (GKE) Benchmark v1.9.0
tech_stack	["kubernetes","gcp","gke"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

4.1.8 Avoid bindings to system:anonymous (Automated)

Profile Applicability

• Level 2

Description

Avoid ClusterRoleBindings nor RoleBindings with the user system:anonymous.

Rationale

Kubernetes assigns user system:anonymous to API server requests that have no authentication information provided. Binding a role to user system:anonymous gives any unauthenticated user the permissions granted by that role and is strongly discouraged.

Impact

Unauthenticated users will have privileges and permissions associated with roles associated with the configured bindings.

Care should be taken before removing any clusterrolebindings or rolebindings from the environment to ensure they were not required for operation of the cluster. Use a more specific and authenticated user for cluster operations.

Audit

Both CusterRoleBindings and RoleBindings should be audited. Use the following command to confirm there are no ClusterRoleBindings to system:anonymous:

$ kubectl get clusterrolebindings -o json   | jq -r '["Name"], ["-----"], (.items[] | select((.subjects | length) > 0) | select(any(.subjects[]; .name == "system:anonymous")) | [.metadata.namespace, .metadata.name]) | @tsv'

There should be no ClusterRoleBindings listed. If any bindings exist, review their permissions with the following command and reassess their privilege.

$ kubectl get clusterrolebinding [CLUSTER_ROLE_BINDING_NAME] -o json \
    | jq ' .roleRef.name +" " + .roleRef.kind' \
    | sed -e 's/"//g' \
    | xargs -l bash -c 'kubectl get $1 $0 -o yaml'

Confirm that there are no RoleBindings including the system:anonymous user:

$ kubectl get rolebindings -A -o json \
  | jq -r '["Namespace", "Name"], ["---------", "-----"], (.items[] | select((.subjects | length) > 0) | select(any(.subjects[]; .name == "system:anonymous")) | [.metadata.namespace, .metadata.name]) | @tsv'

There should be no RoleBindings listed. If any bindings exist, review their permissions with the following command and reassess their privilege.

$ kubectl get rolebinding [ROLE_BINDING_NAME] --namespace [ROLE_BINDING_NAMESPACE] -o json \
    | jq  \
    | sed -e  \
    | xargs -l bash -c