Example: AppStream 2.0 Application Amazon S3 bucket policy cross-service confused deputy prevention - Amazon AppStream 2.0

Example: AppStream 2.0 Application Amazon S3 bucket policy cross-service confused deputy prevention

When you store data in an Amazon S3 bucket, the bucket might be exposed to confused deputy issues. This can leave data such as Elastic fleets, app blocks, setup scripts, application icons, and session scripts vulnerable to malicious actors.

To prevent confused deputy issues, you can specify the aws:SourceAccount condition or the aws:SourceArn condition in the Amazon S3 bucket policy for ELASTIC-FLEET-EXAMPLE-BUCKET.

The resource policies below show how to prevent the confused deputy problem with either of the following:

  • The aws:SourceAccount with your AWS account ID

  • The global condition context key aws:SourceArn

AppStream 2.0 currently doesn't support confused deputy prevention for application icons. The service only supports VHD files and setup scripts. If you try to add additional conditions for application icons, the icons won't be displayed to end users.

In the following example, the bucket policy only allows AppStream 2.0 Elastic fleet resources in the owner's account to access ELASTIC_FLEET_EXAMPLE_BUCKET.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "ConfusedDeputyPreventionExamplePolicy",
            "Effect": "Allow",
            "Principal": {
                "Service": "appstream.amazonaws.com"
            },
            "Action": "s3:GetObject",
            "Resource": [
                "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/vhd-folder/*",
                "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/scripts/*"
            ],
            "Condition": {
                "StringEquals": {
                    "aws:SourceAccount": "your AWS account ID"
                }
            }
        },
        {
            "Sid": "AllowRetrievalPermissionsToS3AppIconsForAppStream",
            "Effect": "Allow",
            "Principal": {
                "Service": "appstream.amazonaws.com"
            },
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/app-icons/*"
        }
    ]
}

You can also use the aws:SourceArn condition to limit resource access for specific resources.

Note

If you don’t know the full ARN of a resource, or you want to specify multiple resources, use the aws:SourceArn global context condition key with wildcards (*) for the unknown portions of the ARN.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "ConfusedDeputyPreventionExamplePolicy",
            "Effect": "Allow",
            "Principal": {
                "Service": "appstream.amazonaws.com"            
            },
            "Action": "s3:GetObject",
            "Resource": [
                "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/vhd-folder/*",
                "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/scripts/*"
            ],
            "Condition": {
                "ArnLike": {
                    "aws:SourceArn": "arn:{aws-partition}:appstream:{your region name}:{your AWS account ID}:app-block/*"
                }
            }
        },
        {
            "Sid": "AllowRetrievalPermissionsToS3AppIconsForAppStream",
            "Effect": "Allow",
            "Principal": {
                "Service": "appstream.amazonaws.com"
            },
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/app-icons/*"
        }
    ]
}

You can use the aws:SourceArn and aws:SourceAccount conditions to limit the resource access for specific resources and accounts.

Note

If you don’t know the full ARN of a resources, or if you want to specify multiple resources, use the aws:SourceArn global context condition key with wildcards (*) for the unknown portions of the ARN.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "ConfusedDeputyPreventionExamplePolicy",
            "Effect": "Allow",
            "Principal": {
                "Service": "appstream.amazonaws.com"            
            },
            "Action": "s3:GetObject",
            "Resource": [
                "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/vhd-folder/*",
                "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/scripts/*"
            ],
            "Condition": {
                "ArnLike": {
                    "aws:SourceArn": "arn:{aws partition}:appstream:{your region name}:{your AWS account ID}:app-block/*"
                }, 
                "StringEquals": {
                    "aws:SourceAccount": "your AWS account ID" 
                }
            }
        },
        {
            "Sid": "AllowRetrievalPermissionsToS3AppIconsForAppStream",
            "Effect": "Allow",
            "Principal": {
                "Service": "appstream.amazonaws.com"
            },
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::ELASTIC-FLEET-EXAMPLE-BUCKET/app-icons/*"
        }
    ]
}