--client-ca-file argument is set as appropriate (Kubelet)
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--client-ca-file argument is set as appropriate (Kubelet)

kubernetes

Classification:

compliance

Framework:

cis-kubernetes

Control:

4.2.3

Set up the kubernetes integration.

Overview

Description

Enable Kubelet authentication using certificates.

Rationale

The connections from the API server 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 API server 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. Enabling Kubelet certificate authentication ensures that the API server could authenticate the Kubelet before submitting any requests.

Audit

Run the following command on each node: ps -ef | grep kubelet. Verify that the --client-ca-file argument exists and is set to the location of the client certificate authority file. If the --client-ca-file argument is not present, check that there is a Kubelet config file specified by --config, and that the file sets authentication: x509: clientCAFile to the location of the client certificate authority file.

Remediation

If using a Kubelet config file, edit the file to set authentication: x509: clientCAFile to the location of the client CA file. If using command line arguments, edit the kubelet service file /etc/systemd/system/kubelet.service.d/10-kubeadm.conf on each worker node and set the below parameter in KUBELET_AUTHZ_ARGS variable.

--client-ca-file=<path/to/client-ca-file>

Based on your system, restart the kubelet service. For example: systemctl daemon-reload systemctl restart kubelet.service

Impact

You require TLS to be configured on API server as well as kubelets.

Default Value

By default, --client-ca-file argument is not set.

References

  1. https://kubernetes.io/docs/admin/kubelet/
  2. https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-authentication-authorization/

CIS Controls

Version 6.14.2 Encrypt All Sensitive Information Over Less-trusted Networks - All communication of sensitive information over less-trusted networks should be encrypted. Whenever information flows over a network with a lower trust level, the information should be encrypted.

Version 7.14.4 Encrypt All Sensitive Information in Transit - Encrypt all sensitive information in transit.