Cis K8S V1120 1.2.5

1.2.5 Ensure that the --kubelet-certificate-authority argument is set as appropriate (Automated)

Profile Applicability

• Level 1 - Master Node

Description

Verify kubelet's certificate before establishing connection.

Rationale

The connections from the apiserver to the kubelet are used for fetching logs for pods, attaching (through kubectl) to running pods, and using the kubelet's port-forwarding functionality. These connections terminate at the kubelet's HTTPS endpoint. By default, the apiserver does not verify the kubelet's serving certificate, which makes the connection subject to man-in-the-middle attacks, and unsafe to run over untrusted and/or public networks.

Impact

You require TLS to be configured on apiserver as well as kubelets.

Audit

Run the following command on the Control Plane node:

ps -ef | grep kube-apiserver

Verify that the --kubelet-certificate-authority argument exists and is set as appropriate.

Alternative Audit

kubectl get pod -nkube-system -lcomponent=kube-apiserver -o=jsonpath='{range .items[]}{.spec.containers[].command} {"\n"}{end}' | grep '--kubelet-certificate-Authority' | grep -i false

If the exit code is '1', then the control isn't present / failed

Remediation

Follow the Kubernetes documentation and setup the TLS connection between the apiserver and kubelets. Then, edit the API server pod specification file /etc/kubernetes/manifests/kube-apiserver.yaml on the Control Plane node and set the --kubelet-certificate-authority parameter to the path to the cert file for the certificate authority.

--kubelet-certificate-authority=<ca-string>

Default Value

By default, --kubelet-certificate-authority argument is not set.

References

1. https://kubernetes.io/docs/admin/kube-apiserver/
2. https://kubernetes.io/docs/admin/kubelet-authentication-authorization/
3. https://kubernetes.io/docs/concepts/cluster-administration/master-node-communication/#apiserver---kubelet

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