The SSH daemon ClientAliveCountMax option must be set correctly.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-67623	AOSX-11-000721	SV-82113r1_rule		Medium

Description

SSH should be configured to log users out after a "15" minute interval of inactivity and to only wait "30" seconds before timing out login attempts. 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 login attempt will also free up resources committed by the managed network element.

STIG	Date
Apple OS X 10.11 Security Technical Implementation Guide	2018-01-04

Details

Check Text ( C-68189r1_chk )
The SSH daemon "ClientAliveCountMax" option must be set correctly. To ensure the SSH idle timeout will occur when the "ClientAliveCountMax" is set, run the following command: /usr/bin/sudo /usr/bin/grep ^ClientAliveCountMax /etc/ssh/sshd_config If the setting is not "ClientAliveCountMax 0", this is a finding.

Fix Text (F-73737r1_fix)
In order to make sure 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