When creating a new environment with AEM as a Cloud Service, the resulting author tier is accessible from the Internet by default. It is possible to configure the network policies further in order to secure the access to your author tier. See Applying an IP Allow List for more details. The procedure is based on authorizing the IP ranges that should be granted network access to your author environment.
In order to put these rules in place, please file a Support ticket, from the Adobe Admin Console with the requested information: