Vulnerability Discussion

Leaving the user list enabled is a security risk since it allows anyone with physical access to the system to enumerate known user accounts without authenticated access to the system.

Check

Verify that RHEL 9 disables the user logon list for graphical user interfaces with the following command:

Note: This requirement assumes the use of the RHEL 9 default graphical user interface, the GNOME desktop environment. If the system does not have any graphical user interface installed, this requirement is Not Applicable.

$ sudo gsettings get org.gnome.login-screen disable-user-list
true

If the setting is "false", this is a finding.

Fix

Configure RHEL 9 to disable the user list at logon for graphical user interfaces.

Create a database to contain the system-wide screensaver settings (if it does not already exist) with the following command:
Note: The example below is using the database "local" for the system, so if the system is using another database in "/etc/dconf/profile/user", the file should be created under the appropriate subdirectory.

$ sudo touch /etc/dconf/db/local.d/02-login-screen

[org/gnome/login-screen]
disable-user-list=true

Update the system databases:

$ sudo dconf update