Check: UBTU-16-030271
Canonical Ubuntu 16.04 LTS STIG:
UBTU-16-030271
(in versions v2 r3 through v1 r4)
Title
The Ubuntu operating system must be configured so that all network connections associated with SSH traffic terminate after a period of inactivity. (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 the operating system automatically terminates a user session after inactivity time-outs have expired. Check for the value of the "ClientAliveCountMax" keyword with the following command: # grep -i clientalivecount /etc/ssh/sshd_config ClientAliveCountMax 0 If "ClientAliveCountMax" is not set to "0", or is commented out, this is a finding.
Fix Text
Configure the Ubuntu operating system to automatically terminates a user session after inactivity time-outs have expired. Modify or append the following line in the "/etc/ssh/sshd_config" file replacing "[CountMax] with a value of "0": ClientAliveCountMax 0 In order for the changes to take effect, the SSH daemon must be restarted. # sudo systemctl restart sshd.service
Additional Identifiers
Rule ID: SV-215130r610931_rule
Vulnerability ID: V-215130
Group Title: SRG-OS-000163-GPOS-00072
Expert Comments
CCIs
| Number | Definition |
|---|---|
| CCI-000879 |
The organization terminates sessions and network connections when nonlocal maintenance is completed. |
| CCI-001133 |
The information system terminates the network connection associated with a communications session at the end of the session or after an organization-defined time period of inactivity. |
| CCI-002361 |
The information system automatically terminates a user session after organization-defined conditions or trigger events requiring session disconnect. |