AWS CDK EKS overly permissive trust policies

If you are using the eks.Cluster or eks.FargateCluster construct we need you to take action. Other users are not affected and can stop reading.

Impact

The AWS Cloud Development Kit (CDK) allows for the definition of Amazon Elastic Container Service for Kubernetes (EKS) clusters. eks.Cluster and eks.FargateCluster constructs create two roles that have an overly permissive trust policy.

The first, referred to as the CreationRole, is used by lambda handlers to create the cluster and deploy Kubernetes resources (e.g KubernetesManifest, HelmChart, ...) onto it. Users with CDK version higher or equal to 1.62.0 (including v2 users) will be affected.

The second, referred to as the default MastersRole, is provisioned only if the mastersRole property isn't provided and has permissions to execute kubectl commands on the cluster. Users with CDK version higher or equal to 1.57.0 (including v2 users) will be affected.

Both these roles use the account root principal in their trust policy, which allows any identity in the account with the appropriate sts:AssumeRole permissions to assume it. For example, this can happen if another role in your account has sts:AssumeRole permissions on Resource: "*".

CreationRole

Users with CDK version higher or equal to 1.62.0 (including v2 users).…