C-0117 - Ensure that the API Server --kubelet-certificate-authority argument is set as appropriate

Framework

cis-v1.23-t1.0.1

Severity

High

Description of the the issue

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.

Related resources

Pod

What does this control test

Verify kubelet's certificate before establishing connection.

How to check it manually

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.

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>

Impact Statement

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

Default Value

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

Example

No example