cis-aks-v170-3.2.2

3.2.2 Ensure that the --authorization-mode argument is not set to AlwaysAllow (Automated)

Profile Applicability

• Level 1

Description

Do not allow all requests. Enable explicit authorization.

Rationale

Kubelets, by default, allow all authenticated requests (even anonymous ones) without needing explicit authorization checks from the apiserver. You should restrict this behavior and only allow explicitly authorized requests.

Impact

Unauthorized requests will be denied.

Audit Procedure

Audit Method 1:

If using a Kubelet configuration file, check that there is an entry for "authentication": "webhook": "enabled" set to true.

First, SSH to the relevant node:

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/kubelet-config.json which is the location of the Kubelet config file.

Open the Kubelet config file:

sudo more /etc/kubernetes/kubelet/kubelet-config.json

Verify that the "authentication": {"webhook": { "enabled": is set to true.

If the "authentication": {"mode": { argument is present check that it is not set to AlwaysAllow. If it is not present check that there is a Kubelet config file specified by --config, and that file sets "authentication": {"mode": { to something other than AlwaysAllow.

Audit Method 2:

If using the api configz endpoint consider searching for the status of authentication... "webhook":{"enabled":true} by extracting the live configuration from the nodes running kubelet.

Set the local proxy port and the following variables and provide proxy port number and node name; HOSTNAME_PORT="localhost-and-port-number" NODE_NAME="The-Name-Of-Node-To-Extract-Configuration" from the output of kubectl get nodes

kubectl proxy --port=8001 &

export HOSTNAME_PORT=localhost:8001 (example host and port number)
export NODE_NAME=ip-192.168.31.226.aks.internal (example node name from "kubectl get nodes")

curl -sSL "http://${HOSTNAME_PORT}/api/v1/nodes/${NODE_NAME}/proxy/configz"

Remediation

Remediation Method 1:

If modifying the Kubelet config file, edit the kubelet-config.json file /etc/kubernetes/kubelet/kubelet-config.json and set the below parameter to false:

"authentication"... "webhook":{"enabled":true

Remediation Method 2:

If using executable arguments, edit the kubelet service file /etc/systemd/system/kubelet.service.d/10-kubelet-args.conf on each worker node and add the below parameter at the end of the KUBELET_ARGS variable string.

--authorization-mode=Webhook

Remediation Method 3:

If using the api configz endpoint consider searching for the status of "authentication.*webhook":{"enabled":"true" by extracting the live configuration from the nodes running kubelet.

**See detailed step-by-step configmap procedures in Reconfigure a Node's Kubelet in a Live Cluster, and then rerun the curl statement from audit process to check for kubelet configuration changes.

For all three remediations: Based on your system, restart the kubelet service and check status:

systemctl daemon-reload
systemctl restart kubelet.service
systemctl status kubelet -l

Default Value

See the Azure AKS documentation for the default value.

References

1. https://kubernetes.io/docs/admin/kubelet/
2. https://kubernetes.io/docs/admin/kubelet-authentication-authorization/#kubelet-authentication
3. https://kubernetes.io/docs/tasks/administer-cluster/reconfigure-kubelet/
4. https://docs.microsoft.com/security/benchmark/azure/security-controls-v2-governance-strategy#gs-6-define-identity-and-privileged-access-strategy

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