Title

The Ubuntu operating system must be configured so that all network connections associated with SSH traffic are terminated at the end of the session or after 10 minutes of inactivity, except to fulfill documented and validated mission requirements. (Cat II impact)

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 Ubuntu operating system functionality where the system owner, data owner, or organization requires additional assurance.

Check Content

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 "ClientAliveInterval" variable is set to a value of "600" or less by performing the following command: # sudo grep -i clientalive /etc/ssh/sshd_config ClientAliveInterval 600 If "ClientAliveInterval" has a value that is greater than "600" and is not documented with the Information System Security Officer (ISSO) as an operational requirement, or is commented out, this is a finding.

Fix Text

Configure the Ubuntu 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 replacing "[Interval]" with a value of "600" or less: ClientAliveInterval 600 In order for the changes to take effect, the SSH daemon must be restarted. # sudo systemctl restart sshd.service

Additional Identifiers

Rule ID: SV-215129r610931_rule

Vulnerability ID: V-215129

Group Title: SRG-OS-000163-GPOS-00072

Expert Comments

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