Ubuntu OS must automatically exit interactive command shell user sessions after five minutes of inactivity.

Terminating an idle interactive command shell user session within a short time period reduces the window of opportunity for unauthorized personnel to take control of it when left unattended in a virtual terminal or physical console.

Verify Ubuntu OS is configured to automatically exit interactive command shell user sessions after five minutes of inactivity or less by using the following command:

     $ sudo grep -E "\bTMOUT=[0-9]+" /etc/bash.bashrc /etc/profile.d/* 
     /etc/profile.d/99-terminal_tmout.sh:TMOUT=300 

If "TMOUT" is not set to "300" or less, is set to "0", is commented out, or missing, this is a finding.

Configure Ubuntu OS to exit interactive command shell user sessions after five minutes of inactivity.

Create and/or append a custom file under "/etc/profile.d/" by using the following command:

     $ sudo su -c "echo TMOUT=300 >> /etc/profile.d/99-terminal_tmout.sh" 

This will set a timeout value of five minutes for all future sessions.

To set the timeout for the current sessions, execute the following command over the terminal session:

     $ export TMOUT=300