Cis Eks V160 3.1.3

3.1.3 Ensure that the kubelet configuration file has permissions set to 644 or more restrictive (Automated)

Profile Applicability

• Level 1

Description

Ensure that if the kubelet refers to a configuration file with the --config argument, that file has permissions of 644 or more restrictive.

Rationale

The kubelet reads various parameters, including security settings, from a config file specified by the --config argument. If this file is specified you should restrict its file permissions to maintain the integrity of the file. The file should be writable by only the administrators on the system.

Audit Procedure

Method 1 - SSH to the relevant worker node:

To check to see if the Kubelet Service is running:

sudo systemctl status kubelet

The output should return Active: active (running) since...

Run the following command on each node to find the appropriate Kubelet config file:

ps -ef | grep kubelet

The output of the above command should return something similar to --config /etc/kubernetes/kubelet/config.json which is the location of the Kubelet config file.

Run the following command:

stat -c %a /etc/kubernetes/kubelet/config.json

The output of the above command is the Kubelet config file's permissions. Verify that the permissions are 644 or more restrictive.

Method 2 - Create and Run a Privileged Pod:

You will need to run a pod that is privileged enough to access the host's file system. This can be achieved by deploying a pod that uses the hostPath volume to mount the node's file system into the pod.

apiVersion: v1
kind: Pod
metadata:
  name: file-check
spec:
  volumes:
    - name: host-root
      hostPath:
        path: /
        type: Directory
  containers:
    - name: nsenter
      image: busybox
      command: ["sleep", "3600"]
      volumeMounts:
        - name: host-root
          mountPath: /host
      securityContext:
        privileged: true

Save this to a file (e.g., file-check-pod.yaml) and create the pod:

kubectl apply -f file-check-pod.yaml

Once the pod is running, you can exec into it to check file permissions on the node:

kubectl exec -it file-check -- sh

Now you are in a shell inside the pod, but you can access the node's file system through the /host directory and check the permission level of the file:

ls -l /host/etc/kubernetes/kubelet/config.json

Verify that if a file is specified and it exists, the permissions are 644 or more restrictive.

Remediation

Run the following command (using the config file location identified in the Audit step):

chmod 644 /etc/kubernetes/kubelet/config.json

Default Value

See the AWS EKS documentation for the default value.

References

1. https://kubernetes.io/docs/tasks/administer-cluster/kubelet-config-file/

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