Cis K8S V1111 4.2.2

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

Profile Applicability

• Level 1 - Worker Node

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

Run the following command on each node:

ps -ef | grep kubelet

If the --authorization-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 authorization: mode to something other than AlwaysAllow.

It is also possible to review the running configuration of a Kubelet via the /configz endpoint on the Kubelet API port (typically 10250/TCP). Accessing these with appropriate credentials will provide details of the Kubelet's configuration.

Remediation

If using a Kubelet config file, edit the file to set authorization: mode to Webhook. If using executable arguments, edit the kubelet service file /etc/kubernetes/kubelet.conf on each worker node and set the below parameter in KUBELET_AUTHZ_ARGS variable.

--authorization-mode=Webhook

Based on your system, restart the kubelet service. For example:

systemctl daemon-reload
systemctl restart kubelet.service

Default Value

By default, --authorization-mode argument is set to AlwaysAllow.

References

1. https://kubernetes.io/docs/admin/kubelet/
2. https://kubernetes.io/docs/admin/kubelet-authentication-authorization/#kubelet-authentication

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