The SUSE operating system for all network connections associated with SSH traffic must immediately terminate at the end of the session or after 10 minutes of inactivity.

STIG ID: SLES-12-030191  |  SRG: SRG-OS-000163-GPOS-00072 |  Severity: medium |  CCI: CCI-001133,CCI-002361 |  Vulnerability Id: V-217273 | 

Vulnerability Discussion

Automatic session termination addresses the termination of user-initiated logical sessions in contrast to the termination of network connections that are associated with communications sessions (i.e., network disconnect). A logical session (for local, network, and remote access) is initiated whenever a user (or process acting on behalf of a user) accesses an organizational information system. Such user sessions can be terminated (and thus terminate user access) without terminating network sessions.

Session termination terminates all processes associated with a user's logical session except those processes that are specifically created by the user (i.e., session owner) to continue after the session is terminated.

Conditions or trigger events requiring automatic session termination can include, for example, organization-defined periods of user inactivity, targeted responses to certain types of incidents, and time-of-day restrictions on information system use.

This capability is typically reserved for specific SUSE operating system functionality where the system owner, data owner, or organization requires additional assurance.

Check

Verify that all network connections associated with SSH traffic are automatically terminated at the end of the session or after "10" minutes of inactivity.

Check that the "ClientAliveCountMax" variable is set to a value of "1" or less by performing the following command:

# sudo grep -i clientalive /etc/ssh/sshd_config

ClientAliveInterval 600

ClientAliveCountMax 1

If "ClientAliveCountMax" does not exist or "ClientAliveCountMax" is not set to a value of "1" in "/etc/ssh/sshd_config", or the line is commented out, this is a finding.

Fix

Configure the SUSE operating system to automatically terminate all network connections associated with SSH traffic at the end of a session or after a "10" minute period of inactivity.

Modify or append the following lines in the "/etc/ssh/sshd_config" file:

ClientAliveCountMax 1

In order for the changes to take effect, the SSH daemon must be restarted.

# sudo systemctl restart sshd.service
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