cis-k8s-v1110-4.2.3

DevOps & Security

Ensure that the --client-ca-file argument is set as appropriate (Automated)

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4.2.3 Ensure that the --client-ca-file argument is set as appropriate (Automated)

Profile Applicability

Level 1 - Worker Node

Description

Enable Kubelet authentication using certificates.

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. Enabling Kubelet certificate authentication ensures that the apiserver could authenticate the Kubelet before submitting any requests.

Impact

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

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/kubernetes/kubelet.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

Default Value

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

References

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	3.10 Encrypt Sensitive Data in Transit		x	x
v7	14.4 Encrypt All Sensitive Information in Transit		x	x