Applies to SUSE Linux Enterprise Server 12 SP5

9 Configuring Security Settings with YaST #

The YaST module Security Center and Hardening offers a central clearinghouse to configure security-related settings for SUSE Linux Enterprise Server. Use it to configure security aspects such as settings for the login procedure and for password creation, for boot permissions, user creation or for default file permissions. Launch it from the YaST control center by Security and Users › Security Center and Hardening. The Security Center dialog always starts with the Security Overview, and other configuration dialogs are available from the right pane.

9.1 Security Overview #

The Security Overview displays a comprehensive list of the most important security settings for your system. The security status of each entry in the list is clearly visible. A green check mark indicates a secure setting while a red cross indicates an entry as being insecure. Click Help to open an overview of the setting and information on how to make it secure. To change a setting, click the corresponding link in the Status column. Depending on the setting, the following entries are available:

Enabled/Disabled: Click this entry to toggle the status of the setting to either enabled or disabled.
Configure: Click this entry to launch another YaST module for configuration. You will return to the Security Overview when leaving the module.
Unknown: A setting's status is set to unknown when the associated service is not installed. Such a setting does not represent a potential security risk.

Figure 9.1: YaST Security Center and Hardening: Security Overview #

9.2 Predefined Security Configurations #

SUSE Linux Enterprise Server comes with three Predefined Security Configurations. These configurations affect all the settings available in the Security Center module. Each configuration can be modified to your needs using the dialogs available from the right pane changing its state to Custom Settings:

Workstation: A configuration for a workstation with any kind of network connection (including a connection to the Internet).
Roaming Device: This setting is designed for a laptop or tablet that connects to different networks.
Network Server: Security settings designed for a machine providing network services such as a Web server, file server, name server, etc. This set provides the most secure configuration of the predefined settings.
Custom Settings: A pre-selected Custom Settings (when opening the Predefined Security Configurations dialog) indicates that one of the predefined sets has been modified. Actively choosing this option does not change the current configuration—you will need to change it using the Security Overview.

9.3 Password Settings #

Passwords that are easy to guess are a major security issue. The Password Settings dialog provides the means to ensure that only secure passwords can be used.

Check New Passwords: By activating this option, a warning will be issued if new passwords appear in a dictionary, or if they are proper names (proper nouns).
Minimum Acceptable Password Length: If the user chooses a password with a length shorter than specified here, a warning will be issued.
Number of Passwords to Remember: When password expiration is activated (via Password Age), this setting stores the given number of a user's previous passwords, preventing their reuse.
Password Encryption Method: Choose a password encryption algorithm. Normally there is no need to change the default (Blowfish).
Password Age: Activate password expiration by specifying a minimum and a maximum time limit (in days). By setting the minimum age to a value greater than 0 days, you can prevent users from immediately changing their passwords again (and in doing so circumventing the password expiration). Use the values 0 and 99999 to deactivate password expiration.
Days Before Password Expires Warning: When a password expires, the user receives a warning in advance. Specify the number of days prior to the expiration date that the warning should be issued.

9.4 Boot Settings #

Configure which users can shut down the machine via the graphical login manager in this dialog. You can also specify how Ctrl–Alt–Del will be interpreted and who can hibernate the system.

9.5 Login Settings #

This dialog lets you configure security-related login settings:

Delay after Incorrect Login Attempt: To make it difficult to guess a user's password by repeatedly logging in, it is recommended to delay the display of the login prompt that follows an incorrect login. Specify the value in seconds. Make sure that users who have mistyped their passwords do not need to wait too long.
Allow Remote Graphical Login: When checked, the graphical login manager (GDM) can be accessed from the network. This is a potential security risk.

9.6 User Addition #

Set minimum and maximum values for user and group IDs. These default settings would rarely need to be changed.

9.7 Miscellaneous Settings #

Other security settings that do not fit the above-mentioned categories are listed here:

File Permissions: SUSE Linux Enterprise Server comes with three predefined sets of file permissions for system files. These permission sets define whether a regular user may read log files or start certain programs. Easy file permissions are suitable for stand-alone machines. These settings allow regular users to, for example, read most system files. See the file /etc/permissions.easy for the complete configuration. The Secure file permissions are designed for multiuser machines with network access. A thorough explanation of these settings can be found in /etc/permissions.secure. The Paranoid settings are the most restrictive ones and should be used with care. See /etc/permissions.paranoid for more information.
User Launching updatedb: The program updatedb scans the system and creates a database of all file locations which can be queried with the command locate. When updatedb is run as user nobody, only world-readable files will be added to the database. When run as user root, almost all files (except the ones root is not allowed to read) will be added.
Enable Magic SysRq Keys: The magic SysRq key is a key combination that enables you to have some control over the system even when it has crashed. The complete documentation can be found at https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html.