3.1.1 Ensure that the kubeconfig file permissions are set to 644 or more restrictive (Automated)
Profile Applicability
Description
If kubelet is running, and if it is configured by a kubeconfig file, ensure that the proxy kubeconfig file has permissions of 644 or more restrictive.
Rationale
The kubelet kubeconfig file controls various parameters of the kubelet service in the worker node. 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.
It is possible to run kubelet with the kubeconfig parameters configured as a Kubernetes ConfigMap instead of a file. In this case, there is no proxy kubeconfig file.
Impact
Ensuring that the kubeconfig file permissions are set to 644 or more restrictive significantly strengthens the security posture of the Kubernetes environment by preventing unauthorized modifications. This restricts write access to the kubeconfig file, ensuring only administrators can alter crucial kubelet configurations, thereby reducing the risk of malicious alterations that could compromise the cluster's integrity.
However, this configuration may slightly impact usability, as it limits the ability for non-administrative users to make quick adjustments to the kubelet settings. Administrators will need to balance security needs with operational flexibility, potentially requiring adjustments to workflows for managing kubelet configurations.
Audit
Using Google Cloud Console
- Go to Kubernetes Engine by visiting https://console.cloud.google.com/kubernetes/list
- Click on the desired cluster to open the Details page, then click on the desired Node pool to open the Node pool Details page
- Note the name of the desired node
- Go to VM Instances by visiting https://console.cloud.google.com/compute/instances
- Find the desired node and click on 'SSH' to open an SSH connection to the node.
Using Command Line
Method 1
SSH to the worker nodes.
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 kubeconfig file:
ps -ef | grep kubelet
The output of the above command should return something similar to --kubeconfig /var/lib/kubelet/kubeconfig which is the location of the kubeconfig file.
Run this command to obtain the kubeconfig file permissions:
stat -c %a /var/lib/kubelet/kubeconfig
The output of the above command gives you the kubeconfig file's permissions. Verify that if a file is specified and it exists, 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.
Here's an example of a simple pod definition that mounts the root of the host to /host within 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/var/lib/kubelet/kubeconfig
Verify that if a file is specified and it exists, the permissions are 644 or more restrictive.
Remediation
Run the below command (based on the file location on your system) on the each worker node. For example,
chmod 644 <kubeconfig file>
Default Value
See the GKE documentation for the default value.
References
- https://cloud.google.com/kubernetes-engine/docs/concepts/cis-benchmarks
CIS Controls
| Controls Version | Control | IG 1 | IG 2 | IG 3 |
|---|
| v8 | 3.3 Configure Data Access Control Lists - Configure data access control lists based on a user's need to know. Apply data access control lists, also known as access permissions, to local and remote file systems, databases, and applications. | X | X | X |
| v8 | 13.4 Perform Traffic Filtering Between Network Segments - Perform traffic filtering between network segments, where appropriate. | | X | X |
| v8 | 13.6 Collect Network Traffic Flow Logs - Collect network traffic flow logs and/or network traffic to review and alert upon from network devices. | | X | X |
| v7 | 5.2 Maintain Secure Images - Maintain secure images or templates for all systems in the enterprise based on the organization's approved configuration standards. Any new system deployment or existing system that becomes compromised should be imaged using one of those images or templates. | | X | X |
