Cis Aks V180 3.2.8

3.2.8 Ensure that the --rotate-certificates argument is not set to false (Automated)

Profile Applicability

• Level 2

Description

Enable kubelet client certificate rotation.

Rationale

The --rotate-certificates setting causes the kubelet to rotate its client certificates by creating new CSRs as its existing credentials expire. This automated periodic rotation ensures that the there is no downtime due to expired certificates and thus addressing availability in the CIA (Confidentiality, Integrity, and Availability) security triad.

Note: This recommendation only applies if you let kubelets get their certificates from the API server. In case your kubelet certificates come from an outside authority/tool (e.g. Vault) then you need to implement rotation yourself.

Note: This feature also requires the RotateKubeletClientCertificate feature gate to be enabled.

Impact

None

Audit Procedure

Audit Method 1:

SSH to each node and run the following command to find the Kubelet process:

ps -ef | grep kubelet

If the output of the command above includes the --RotateCertificate executable argument, verify that it is set to true. If the output of the command above does not include the --RotateCertificate executable argument then check the Kubelet config file. The output of the above command should return something similar to --config /etc/kubernetes/kubelet/kubelet-config.json which is the location of the Kubelet config file.

Open the Kubelet config file:

cat /etc/kubernetes/kubelet/kubelet-config.json

Verify that the RotateCertificate argument is not present, or is set to true.

Remediation

Remediation Method 1:

If modifying the Kubelet config file, edit the kubelet-config.json file /etc/kubernetes/kubelet/kubelet-config.json and set the below parameter to true:

"RotateCertificate":true

Additionally, ensure the kubelet service file /etc/systemd/system/kubelet.service.d/10-kubelet-args.conf does not set the --RotateCertificate executable argument to false because this would override the Kubelet config file.

Remediation Method 2:

If using executable arguments, edit the kubelet service file /etc/systemd/system/kubelet.service.d/10-kubelet-args.conf on each worker node and add the below parameter at the end of the KUBELET_ARGS variable string.

--RotateCertificate=true

Default Value

See the AKS documentation for the default value.

References

1. https://github.com/kubernetes/kubernetes/pull/41912
2. https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/#kubelet-configuration
3. https://kubernetes.io/docs/imported/release/notes/
4. https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/
5. https://kubernetes.io/docs/tasks/administer-cluster/reconfigure-kubelet/
6. https://docs.microsoft.com/security/benchmark/azure/security-controls-v2-data-protection#dp-4-encrypt-sensitive-information-in-transit

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