======5.2.13 Ensure SSH Idle Timeout Interval is configured (Scored)======
=====Profile Applicability=====  
<code>
Level 1 - Server
Level 1 - Workstation 
</code>

=====Description=====
The two options ''ClientAliveInterval'' and ''ClientAliveCountMax'' control the timeout of ssh sessions. When the ''ClientAliveInterval'' variable is set, ssh sessions that have no activity for the specified length of time are terminated. When the ''ClientAliveCountMax'' variable is set, sshd will send client alive messages at every ''ClientAliveInterval'' interval. When the number of consecutive client alive messages are sent with no response from the client, the ssh session is terminated. For example, if the ''ClientAliveInterval'' is set to 15 seconds and the ''ClientAliveCountMax'' is set to 3, the client ''ssh'' session will be terminated after 45 seconds of idle time.

=====Rationale=====
Having no timeout value associated with a connection could allow an unauthorized user access to another user's ''ssh'' session (e.g. user walks away from their computer and doesn't lock the screen). Setting a timeout value at least reduces the risk of this happening..
While the recommended setting is 300 seconds (5 minutes), set this timeout value based on site policy. The recommended setting for ''ClientAliveCountMax'' is 0. In this case, the client session will be terminated after 5 minutes of idle time and no keepalive messages will be sent.

=====Audit===== 
Run the following commands and verify ''ClientAliveInterval'' is 300 or less and ''ClientAliveCountMax'' is 3 or less:
<Code:bash>
# grep "^ClientAliveInterval" /etc/ssh/sshd_config 
ClientAliveInterval 300 
# grep "^ClientAliveCountMax" /etc/ssh/sshd_config 
ClientAliveCountMax 0
</Code>

=====Remediation===== 
Edit the ''/etc/ssh/sshd_config'' file to set the parameter as follows:
<Code:bash>
ClientAliveInterval 300 
ClientAliveCountMax 0
</Code>