Cross-service confused deputy prevention - AWS DataSync

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 and aws:SourceAccount global condition context keys in resource policies to limit the permissions that AWS DataSync gives another service to the resource. If you use both global condition context keys and the aws:SourceArn value contains the account ID, 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. Use aws:SourceArn if you want only one resource to be associated with the cross-service access. Use aws:SourceAccount if you want any resource in that account to be associated with the cross-service use.

The value of aws:SourceArn must include the DataSync location ARN with which DataSync is allowed to assume the IAM role.

The most effective way to protect against the confused deputy problem is to use the aws:SourceArn key with the full ARN of the resource. If you don't know the full ARN or if you're specifying multiple resources, use wildcard characters (*) for the unknown portions. Here are some examples of how to do this for DataSync:

  • To limit the trust policy to an existing DataSync location, include the full location ARN in the policy. DataSync will assume the IAM role only when dealing with that particular location.

  • When creating an Amazon S3 location for DataSync, you don't know the location's ARN. In these scenarios, use the following format for the aws:SourceArn key: arn:aws:datasync:us-east-2:123456789012:*. This format validates the partition (aws), account ID, and Region.

The following full example shows how you can use the aws:SourceArn and aws:SourceAccount global condition context keys in a trust policy to prevent the confused deputy problem with DataSync.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "Service": "datasync.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {
                "StringEquals": {
                    "aws:SourceAccount": "123456789012"
                },
                "StringLike": {
                    "aws:SourceArn": "arn:aws:datasync:us-east-2:123456789012:*"
                }
            }
        }
    ]
}

For more example policies that show how you can use the aws:SourceArn and aws:SourceAccount global condition context keys with DataSync, see the following topics: