Cross-service confused deputy prevention - AWS Clean Rooms

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 AWS, 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 should not otherwise have permission to access. To prevent this, AWS provides tools that help you protect your data for all services with service principals that have been given access to resources in your account.

We recommend using the aws:SourceArn global condition context keys in resource policies to limit the permissions that AWS Clean Rooms gives another service to the resource. Use aws:SourceArn if you want only one resource to be associated with the cross-service access.

The most effective way to protect against the confused deputy problem is to use the aws:SourceArn global condition context key with the full ARN of the resource. In AWS Clean Rooms, you also have to compare against the sts:ExternalId condition key.

The value of aws:SourceArn must be set to the ARN of the membership of the assumed role.

The following example shows how you can use the aws:SourceArn global condition context key in AWS Clean Rooms to prevent the confused deputy problem.

Note

The example policy applies to the trust policy of the service role that AWS Clean Rooms uses to access customer data.

The value of membershipID is your AWS Clean Rooms membership ID in the collaboration. 

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowIfExternalIdMatches",
            "Effect": "Allow",
            "Principal": {
                "Service": "cleanrooms.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {
                "StringLike": {
                    "sts:ExternalId": "arn:aws:*:aws-region:*:dbuser:*/membershipID*"
                }
            }
        },
        {
            "Sid": "AllowIfSourceArnMatches",
            "Effect": "Allow",
            "Principal": {
                "Service": "cleanrooms.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {
                "ForAnyValue:ArnEquals": {
                    "aws:SourceArn": "arn:aws:cleanrooms:aws-region:123456789012:membership/membershipID"
                }
            }
        }
    ]
}