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Cross-service confused deputy prevention - AWS End User Messaging

Cross-service confused deputy prevention

The confused deputy problem is a security issue where an entity that does not 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 the resources of another customer 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 End User Messaging gives another service to 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. If you do not know the full ARN of the resource, or if you are specifying multiple resources, use the aws:SourceArn global condition context key with wildcard characters (*) for the unknown portions of the ARN. For example, arn:aws:servicename:*:123456789012:*.

If the aws:SourceArn value does not contain the account ID, such as an Amazon S3 bucket ARN, you must use both global condition context keys to limit permissions. The value of aws:SourceArn must be the ARN of the phone number.

The following example shows how you can use the aws:SourceArn and aws:SourceAccount global condition context keys in AWS End User Messaging to prevent the confused deputy problem.

{
  "Version": "2012-10-17",
  "Statement": {
    "Sid": "ConfusedDeputyPreventionExamplePolicy",
    "Effect": "Allow",
    "Principal": {
      "Service": "sms-voice.amazonaws.com"
    },
    "Action": "sns:Publish",
    "Resource": "*",
    "Condition": {
      "StringEquals": {
        "aws:SourceAccount": "111122223333"
      },
      "ArnLike": {
        "aws:SourceArn": "arn:aws:sms-voice:us-east-1:111122223333:phone-number/PhoneNumberID"
      }
    }
  }
 }

The preceding example applies to the SMS, MMS, voice, and RCS channels, which use the sms-voice.amazonaws.com service principal and sms-voice resource ARNs. For the WhatsApp channel, use the social-messaging.amazonaws.com service principal and social-messaging resource ARNs instead. For example, set aws:SourceArn to arn:aws:social-messaging:*:123456789012:* to scope access to resources in your account.