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Profile applicability: Level 1 - Master Node
The Kubernetes API stores secrets, which may be service account tokens for the Kubernetes API or credentials used by workloads in the cluster. Access to these secrets should be restricted to the smallest possible group of users to reduce the risk of privilege escalation.
Inappropriate access to secrets stored within the Kubernetes cluster can allow for an attacker to gain additional access to the Kubernetes cluster or external resources whose credentials are stored as secrets.
Note
Note
By default in a kubeadm cluster the following list of principals have get privileges on secret objects. 
CLUSTERROLEBINDING                                SUBJECT
TYPE                          SA-NAMESPACE
cluster-admin                                              system:masters
Group
system:controller:clusterrole-aggregation-controller       clusterroleaggregation-
controller ServiceAccount kube-system
system:controller:expand-controller                        expand-controller
ServiceAccount kube-system
system:controller:generic-garbage-collector                generic-garbagecollector
ServiceAccount kube-system
system:controller:namespace-controller                     namespace-controller
ServiceAccount kube-system
system:controller:persistent-volume-binder                 persistent-volumebinder
ServiceAccount kube-system
system:kube-controller-manager                             system:kube-controllermanager
User

Impact

Care should be taken not to remove access to secrets to system components which require this for their operation.

Audit

Review the users who have get, list, or watch access to secrets objects in the Kubernetes API.

Remediation

Where possible, restrict access to secret objects in the cluster by removing get, list, and watch permissions.