Cross-service confused deputy prevention

The confused deputy problem is a security issue where an entity that doesn't have permission to perform an action can coerce a more-privileged entity to perform the action. In Amazon, cross-service impersonation can result in the confused deputy problem. Cross-service impersonation can occur when one service (the calling service) calls another service (the called service). The calling service can be manipulated to use its permissions to act on another customer's resources in a way it shouldn't otherwise have permission to access. To prevent this, Amazon provides tools that help you protect your data for all services with service principals that have been given access to resources in your account.

To limit the permissions that Amazon IoT gives another service to the resource, we recommend using the aws:SourceArn and aws:SourceAccount global condition context keys in resource policies. If you use both global condition context keys, the aws:SourceAccount value and the account in the aws:SourceArn value must use the same account ID when used in the same policy statement.

The most effective way to protect against the confused deputy problem is to use the aws:SourceArn global condition context key with the full Amazon Resource Name (ARN) of the resource. For Amazon IoT, your aws:SourceArn must comply with the format: arn:aws:iot:region:account-id:*. Make sure that the region matches your Amazon IoT Region and the account-id matches your customer account ID.

The following example shows how to prevent the confused deputy problem by using the aws:SourceArn and aws:SourceAccount global condition context keys in the Amazon IoT role trust policy.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": "iot.amazonaws.com"
      },
      "Action": "sts:AssumeRole",
      "Condition": {
        "StringEquals": {
          "aws:SourceAccount": "123456789012"
        },
        "ArnLike": {
          "aws:SourceArn": "arn:aws:iot:us-east-1:123456789012:*"
        }
      }
    }
  ]
}