IIST-SI-000221 - Anonymous IIS 10.0 website access accounts must be restricted - Anonymous username
Many of the security problems that occur are not the result of a user gaining access to files or data for which the user does not have permissions, but rather users are assigned incorrect permissions to unauthorized data. The files, directories, and data stored on the web server must be evaluated and a determination made concerning authorized access to information and programs on the server. Only authorized users and administrative accounts will be allowed on the host server in order to maintain the web server, applications, and review the server operations.
Remove the Anonymous access account from all privileged accounts and all privileged groups.