Ensure there are no public file systems for AWS Elastic File System (EFS)

Allowing unrestricted, public access to cloud services could open an application up to external attack. Disallowing this access is typically considered best practice.

In AWS Console -

1. Sign in to the AWS Console and go to the Amazon EFS console.
2. Select File Systems.
3. Click the file system that you want to configure. Select Permissions.
4. In the File system policy, select the policy statement.
5. Click Edit and make the necessary changes.

In Terraform -

1. In the aws_efs_file_system_policy resource, configure the policy field accordingly.

References:
https://docs.aws.amazon.com/efs/latest/ug/auth-and-access-control.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/efs_file_system_policy