The SSH daemon must restrict login ability to specific users and/or groups.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-22470	GEN005521	SV-37843r2_rule		Medium

Description
Restricting SSH logins to a limited group of users, such as system administrators, prevents password-guessing and other SSH attacks from reaching system accounts and other accounts not authorized for SSH access.

STIG	Date
Red Hat Enterprise Linux 5 Security Technical Implementation Guide	2016-12-16

Details

Check Text ( C-37041r1_chk )
There are two ways in which access to SSH may restrict users or groups. Check if /etc/pam.d/sshd is configured to require daemon style login control. # grep pam_access.so /etc/pam.d/sshd\|grep "required"\|grep "account"\| grep -v '^#' If no lines are returned, sshd is not configured to use pam_access. Check the SSH daemon configuration for the AllowGroups setting. # egrep -i "AllowGroups\|AllowUsers" /etc/ssh/sshd_config \| grep -v '^#' If no lines are returned, sshd is not configured to limit access to users/groups. If sshd is not configured to limit access either through pam_access or the use "AllowUsers" or "Allowgroups", this is a finding.

Check Text ( C-37041r1_chk )

There are two ways in which access to SSH may restrict users or groups.

Check if /etc/pam.d/sshd is configured to require daemon style login control.
# grep pam_access.so /etc/pam.d/sshd|grep "required"|grep "account"| grep -v '^#'
If no lines are returned, sshd is not configured to use pam_access.

Check the SSH daemon configuration for the AllowGroups setting.
# egrep -i "AllowGroups|AllowUsers" /etc/ssh/sshd_config | grep -v '^#'
If no lines are returned, sshd is not configured to limit access to users/groups.

If sshd is not configured to limit access either through pam_access or the use "AllowUsers" or "Allowgroups", this is a finding.

Fix Text (F-32309r2_fix)
Edit the SSH daemon configuration and add an "AllowGroups" or "AllowUsers" directive specifying the groups and users allowed to have access. Restart the SSH daemon. # /sbin/service sshd restart Alternatively, modify the /etc/pam.d/sshd file to include the line account required pam_access.so accessfile= If the "accessfile" option is not specified the default "access.conf" file will be used. The "access.conf" file must contain the user restriction definitions.

Fix Text (F-32309r2_fix)

Edit the SSH daemon configuration and add an "AllowGroups" or "AllowUsers" directive specifying the groups and users allowed to have access.

Restart the SSH daemon.
# /sbin/service sshd restart

Alternatively, modify the /etc/pam.d/sshd file to include the line

account required pam_access.so accessfile=

If the "accessfile" option is not specified the default "access.conf" file will be used. The "access.conf" file must contain the user restriction definitions.