Cis K8S V1120 1.2.3

1.2.3 Ensure that the DenyServiceExternalIPs is set (Manual)

Profile Applicability

• Level 1 - Master Node

Description

This admission controller rejects all net-new usage of the Service field externalIPs.

Rationale

Most users do not need the ability to set the externalIPs field for a Service at all, and cluster admins should consider disabling this functionality by enabling the DenyServiceExternalIPs admission controller. Clusters that do need to allow this functionality should consider using some custom policy to manage its usage.

Impact

When enabled, users of the cluster may not create new Services which use externalIPs and may not add new values to externalIPs on existing Service objects.

Audit

Run the following command on the Control Plane node:

ps -ef | grep kube-apiserver

Verify that the DenyServiceExternalIPs argument exist as a string value in --enable-admission-plugins.

Remediation

Edit the API server pod specification file /etc/kubernetes/manifests/kube-apiserver.yaml on the master node and append the Kubernetes API server flag --enable-admission-plugins with the DenyServiceExternalIPs plugin. Note, the Kubernetes API server flag --enable-admission-plugins takes a comma-delimited list of admission control plugins to be enabled, even if they are in the list of plugins enabled by default.

kube-apiserver --enable-admission-plugins=DenyServiceExternalIPs

Default Value

By default, --enable-admission-plugins=DenyServiceExternalIP argument is not set, and the use of externalIPs is authorized.

References

1. https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/
2. https://kubernetes.io/docs/admin/kube-apiserver/

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