AWS CDK EKS overly permissive trust policies

AWS Cloud Development Kit (AWS CDK) is an open-source software development framework to define cloud infrastructure in code and provision it through AWS CloudFormation. In the packages aws-cdk-lib 2.0.0 until 2.80.0 and @aws-cdk/aws-eks 1.57.0 until 1.202.0, eks.Cluster and eks.FargateCluster constructs create two roles, CreationRole and default MastersRole, 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) may 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) may be affected.

The issue has been fixed in @aws-cdk/aws-eks v1.202.0 and aws-cdk-lib v2.80.0. These versions no longer use the account root principal. Instead, they restrict the trust policy to the specific roles of lambda handlers that need it. There is no workaround available for CreationRole. To avoid creating the default MastersRole, use the mastersRole property to explicitly provide a role.