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 CodeDeploy 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.

For EC2/On-Premises, AWS Lambda, and regular Amazon ECS deployments, the value of aws:SourceArn should include the CodeDeploy deployment group ARN with which CodeDeploy is allowed to assume the IAM role.

For Amazon ECS blue/green deployments created through AWS CloudFormation, the value of aws:SourceArn should include the CloudFormation stack ARN with which CodeDeploy 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.

For example, you might use the following trust policy with a EC2/On-Premises, AWS Lambda, or regular Amazon ECS deployment:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "",
            "Effect": "Allow",
            "Principal": {
                "Service": "codedeploy.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {
                "StringEquals": {
                    "aws:SourceAccount": "111122223333"
                },
                "StringLike": {
                    "aws:SourceArn": "arn:aws:codedeploy:us-east-1:111122223333:deploymentgroup:myApplication/*"
                }
            }
        }
    ]
}

For an Amazon ECS blue/green deployment created through AWS CloudFormation, you might use:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "",
            "Effect": "Allow",
            "Principal": {
                "Service": "codedeploy.amazonaws.com"
            },
            "Action": "sts:AssumeRole",
            "Condition": {
                "StringEquals": {
                    "aws:SourceAccount": "111122223333"
                },
                "StringLike": {
                    "aws:SourceArn": "arn:aws:cloudformation:us-east-1:111122223333:stack/MyCloudFormationStackName/*"
                }
            }
        }
    ]
}