The macOS system must be configured with the SSH daemon ClientAliveCountMax option set to 0.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-252457	APPL-12-000052	SV-252457r858507_rule		Medium

Description
SSH should be configured with an Active Client Alive Maximum Count of 0. 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 or an incomplete logon attempt will also free up resources committed by the managed network element.

Description

SSH should be configured with an Active Client Alive Maximum Count of 0. 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 or an incomplete logon attempt will also free up resources committed by the managed network element.

STIG	Date
Apple macOS 12 (Monterey) Security Technical Implementation Guide	2022-09-07

Details

Check Text ( C-55913r858506_chk )
If SSH is not being used, this is Not Applicable. The SSH daemon "ClientAliveCountMax" option must be set correctly. To verify the SSH idle timeout will occur when the "ClientAliveCountMax" is set, run the following command: /usr/bin/grep -r ^ClientAliveCountMax /etc/ssh/sshd_config* If the setting is not "ClientAliveCountMax 0", this is a finding. If conflicting results are returned, this is a finding.

Check Text ( C-55913r858506_chk )

If SSH is not being used, this is Not Applicable.

The SSH daemon "ClientAliveCountMax" option must be set correctly. To verify the SSH idle timeout will occur when the "ClientAliveCountMax" is set, run the following command:

/usr/bin/grep -r ^ClientAliveCountMax /etc/ssh/sshd_config*

If the setting is not "ClientAliveCountMax 0", this is a finding.
If conflicting results are returned, this is a finding.

Fix Text (F-55863r816184_fix)
To ensure that the SSH idle timeout occurs precisely when the "ClientAliveCountMax" is set, run the following command: /usr/bin/sudo /usr/bin/sed -i.bak 's/.ClientAliveCountMax./ClientAliveCountMax 0/' /etc/ssh/sshd_config