The username is one part of logon credentials that could be used to gain access to a system. Preventing the enumeration of users limits this information to authorized personnel.
Check
This applies to member servers. For domain controllers and stand-alone or nondomain-joined systems, this is not applicable.
If the following registry value does not exist or is not configured as specified, this is a finding:
Configure the policy value for Computer Configuration >> Administrative Templates >> System >> Logon >> Enumerate local users on domain-joined computers to "Disabled".