The macOS system must be configured with the SSH daemon ClientAliveInterval option set to 900 or less.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-225139	AOSX-15-000051	SV-225139r485636_rule		Medium

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

Description

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

STIG	Date
Apple OS X 10.15 (Catalina) Security Technical Implementation Guide	2020-08-13

Details

Check Text ( C-26838r467585_chk )
The SSH daemon "ClientAliveInterval" option must be set correctly. To check the idle timeout setting for SSH sessions, run the following: /usr/bin/sudo /usr/bin/grep ^ClientAliveInterval /etc/ssh/sshd_config If the setting is not "900" or less, this is a finding.

Fix Text (F-26826r467586_fix)
To ensure that "ClientAliveInterval" is set correctly, run the following command: /usr/bin/sudo /usr/bin/sed -i.bak 's/.ClientAliveInterval./ClientAliveInterval 900/' /etc/ssh/sshd_config