Cis Ubuntu2004 V300 1 7 3

1.7.3 Ensure GDM disable-user-list option is enabled (Automated)

Profile

• Level 1 - Server
• Level 1 - Workstation

Description

GDM is the GNOME Display Manager which handles graphical login for GNOME based systems.

The disable-user-list option controls if a list of users is displayed on the login screen.

Rationale

Displaying the user list eliminates half of the Userid/Password equation that an unauthorized person would need to log on.

Audit Procedure

Command Line

Run the following command to verify that a user profile exists:

# grep -Psi "user-db|system-db" /etc/dconf/profile/*/*

/etc/dconf/profile/local:user-db:user
/etc/dconf/profile/local:system-db:local

Run the following command and to verify that the disable-user-list option is enabled:

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

Expected Result

• A user profile should exist
• disable-user-list should be true

Remediation

Command Line

• IF - A user profile exists run the following command to enable the disable-user-list:

# gsettings set org.gnome.login-screen disable-user-list true

Note:

• gsettings commands in this section MUST be done from a command window on a graphical desktop or an error will be returned.

• The system must be restarted after all gsettings configurations have been set in order for CIS-CAT Assessor to appropriately assess.

• OR/IF - A user profile does not exist:

1. Create or edit the gdm profile in /etc/dconf/profile/gdm with the following lines:

user-db:user
system-db:gdm
file-db:/usr/share/gdm/greeter-dconf-defaults

Note: gdm is the name of a dconf database.

2. Create a gdm keyfile for machine-wide settings in /etc/dconf/db/gdm.d/00-login-screen:

[org/gnome/login-screen]
# Do not show the user list
disable-user-list=true

3. Update the system databases:

# dconf update

Note: When the user profile is created or changed, the user will need to log out and log in again before the changes will be applied.

Default Value

false

References

1. https://help.gnome.org/admin/system-admin-guide/stable/login-userlist-disable.html.en
2. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5

Additional Information

If a different GUI login service is in use and required on the system, consult your documentation to disable displaying the user list.

MITRE ATT&CK Mappings: T1078, T1078.001, T1078.002, T1078.003, T1087, T1087.001, T1087.002 | TA0007 | M1028