cis-gke-v180-5-4-1

name	cis-gke-v180-5.4.1
description	Ensure the GKE Metadata Server is Enabled (Automated)
category	cis-gke
version	1.8.0
author	cyberstrike-official
tags	["cis","gke","kubernetes","gcp","node-metadata","metadata-server"]
cis_id	5.4.1
cis_benchmark	CIS Google Kubernetes Engine (GKE) Benchmark v1.8.0
tech_stack	["kubernetes","gcp","gke"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

5.4.1 Ensure the GKE Metadata Server is Enabled (Automated)

Profile Applicability

• Level 2

Description

Running the GKE Metadata Server prevents workloads from accessing sensitive instance metadata and facilitates Workload Identity.

Rationale

Every node stores its metadata on a metadata server. Some of this metadata, such as kubelet credentials and the VM instance identity token, is sensitive and should not be exposed to a Kubernetes workload. Enabling the GKE Metadata server prevents pods (that are not running on the host network) from accessing this metadata and facilitates Workload Identity.

When unspecified, the default setting allows running pods to have full access to the node's underlying metadata server.

Impact

The GKE Metadata Server must be run when using Workload Identity. Because Workload Identity replaces the need to use Metadata Concealment, the two approaches are incompatible.

When the GKE Metadata Server and Workload Identity are enabled, unless the Pod is running on the host network, Pods cannot use the the Compute Engine default service account.

Workloads may need modification in order for them to use Workload Identity as described within: https://cloud.google.com/kubernetes-engine/docs/how-to/workload-identity.

Audit

Using Google Cloud Console

1. Go to Kubernetes Engine by visiting https://console.cloud.google.com/kubernetes/list
2. From the list of clusters, click on the name of the cluster of interest and for each Node pool within the cluster, open the Details pane, and ensure that the GKE Metadata Server is set to Enabled.

Using Command Line To check whether the GKE Metadata Server is enabled for each Node pool within a cluster define 2 variables for Cluster Name and Zone and then run the following command:

gcloud container clusters describe $CLUSTER_NAME --zone $COMPUTE_ZONE --format json | jq '.nodePools[].config.workloadMetadataConfig'

This should return the following for each Node pool:

{
  "mode": "GKE_METADATA"
}

Null ({ }) is returned if the GKE Metadata Server is not enabled.

Remediation

The GKE Metadata Server requires Workload Identity to be enabled on a cluster. Modify the cluster to enable Workload Identity and enable the GKE Metadata Server.