Confused deputy prevention in EventBridge Scheduler

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 your schedule execution role to limit the permissions that EventBridge Scheduler gives another service to access the resource. Use aws:SourceArn if you want only one resource to be associated with the cross-service access. Use aws:SourceAccount if you want to allow any resource in that account to be associated with the cross-service use.

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. The following condition is scoped to an individual schedule group: arn:aws:scheduler:*:123456789012:schedule-group/your-schedule-group

If you don't know the full ARN of the resource or if you are specifying multiple resources, use the aws:SourceArn global context condition key with wildcard characters (*) for the unknown portions of the ARN. For example: arn:aws:scheduler:*:123456789012:schedule-group/*.

The value of aws:SourceArn must be your EventBridge Scheduler schedule group ARN to which you want to scope this condition.

Important

Do not scope the aws:SourceArn statement to a specific schedule or a schedule name prefix. The ARN you specify must be a schedule group.

The following example shows how you can use the aws:SourceArn and aws:SourceAccount global condition context keys in your execution role trust policy to prevent the confused deputy problem:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "Service": "scheduler.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {
                "StringEquals": {
                    "aws:SourceAccount": "123456789012",
                    "aws:SourceArn": "arn:aws:scheduler:us-west-2:123456789012:schedule-group/your-schedule-group"
                }
            }
        }
    ]
}