Title

Ubuntu 24.04 LTS must immediately terminate all network connections associated with SSH traffic at the end of the session or after 10 minutes of inactivity. (Cat II impact)

Discussion

Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended. In addition, quickly terminating an idle session will also free up resources committed by the managed network element. Terminating network connections associated with communications sessions includes, for example, de-allocating associated TCP/IP address/port pairs at Ubuntu 24.04 LTS level, and de-allocating networking assignments at the application level if multiple application sessions are using a single operating system-level network connection. This does not mean that Ubuntu 24.04 LTS terminates all sessions or network access; it only ends the inactive session and releases the resources associated with that session.

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 with the following command: $ grep -ir ClientAliveInterval /etc/ssh/sshd_config* /etc/ssh/sshd_config:ClientAliveInterval 600 If "ClientAliveInterval" does not exist, is not set to a value of "600" or less in "/etc/ssh/sshd_config", if conflicting results are returned, is commented out, or is missing, this is a finding.

Fix Text

Configure Ubuntu 24.04 LTS to automatically terminate all network connections associated with SSH traffic at the end of a session or after a 10-minute period of inactivity. In the file /etc/ssh/sshd_config set ClientAliveInterval to a value of "600" or less: ClientAliveInterval 600 Restart the SSH daemon for the changes to take effect: $ sudo systemctl restart sshd.service

Additional Identifiers

Rule ID: SV-270743r1066718_rule

Vulnerability ID: V-270743

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

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.