Cis Oke V150 3.2.10

3.2.10 Ensure that the --rotate-server-certificates argument is set to true (Automated)

Profile Applicability

• Level 1

Description

Enable kubelet server certificate rotation.

Rationale

--rotate-server-certificates causes the kubelet to both request a serving certificate after bootstrapping its client credentials and rotate the certificate as its existing credentials expire. This automated periodic rotation ensures that the there are no downtimes due to expired certificates and thus addressing availability in the CIA 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 take care of rotation yourself.

Impact

None

Audit Procedure

Audit Method 1: If using a Kubelet configuration file, check that there is an entry for --rotate-server-certificates is set to true. First, SSH to the relevant node: Run the following command on each node to find the appropriate Kubelet config file:

find / -name kubelet.service

The output of the above command should return the file and location /etc/systemd/system/kublet.service which is the location of the Kubelet service config file. Open the Kubelet service config file:

sudo more etc/systemd/system/kublet.service

Verify that the --rotate-server-certificates=true.

Audit Method 2: If using the api configz endpoint consider searching for the status of --rotate-server-certificates by extracting the live configuration from the nodes running kubelet. Set the local proxy port and the following variables and provide proxy port number and node name; HOSTNAME_PORT="localhost-and-port-number" NODE_NAME="The-Name-Of-Node-To-Extract-Configuration" from the output of "kubectl get nodes"

kubectl proxy --port=8001 &

export HOSTNAME_PORT=localhost:8001 (example host and port number)
export NODE_NAME=10.0.10.4 (example node name from "kubectl get nodes")

curl -sSL "http://${HOSTNAME_PORT}/api/v1/nodes/${NODE_NAME}/proxy/configz"

Remediation

Remediation Method 1: If modifying the Kubelet service config file, edit the kubelet.service file /etc/systemd/system/kubelet.service and set the below parameter

--rotate-server-certificates=true

Remediation Method 2: If using the api configz endpoint consider searching for the status of --rotate-server-certificates by extracting the live configuration from the nodes running kubelet. **See detailed step-by-step configmap procedures in Reconfigure a Node's Kubelet in a Live Cluster, and then rerun the curl statement from audit process to check for kubelet configuration changes

kubectl proxy --port=8001 &

export HOSTNAME_PORT=localhost:8001 (example host and port number)
export NODE_NAME=10.0.10.4 (example node name from "kubectl get nodes")

curl -sSL "http://${HOSTNAME_PORT}/api/v1/nodes/${NODE_NAME}/proxy/configz"

For all remediations: Based on your system, restart the kubelet service and check status

systemctl daemon-reload
systemctl restart kubelet.service
systemctl status kubelet -l

Default Value

See the OKE documentation for the default value.

References

1. https://github.com/kubernetes/kubernetes/pull/45059
2. https://kubernetes.io/docs/admin/kubelet-tls-bootstrapping/#kubelet-configuration
3. https://docs.cloud.oracle.com/en-us/iaas/Content/ContEng/Concepts/contengoverview.htm
4. https://kubernetes.io/docs/reference/access-authn-authz/kubelet-tls-bootstrapping/#certificate-rotation

CIS Controls

MITRE ATT&CK Mappings

Profile: Level 1 - CIS Oracle Cloud Infrastructure Container Engine for Kubernetes (OKE) Benchmark v1.5.0