RHEL 9 must not allow users to override SSH environment variables.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257993	RHEL-09-255085	SV-257993r991591_rule		Medium

Description
SSH environment options potentially allow users to bypass access restriction in some configurations.

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2024-06-04

Details

Check Text ( C-61734r952191_chk )
Verify that unattended or automatic logon via SSH is disabled with the following command: $ sudo /usr/sbin/sshd -dd 2>&1 \| awk '/filename/ {print $4}' \| tr -d '\r' \| tr '\n' ' ' \| xargs sudo grep -iH '^\s*permituserenvironment' PermitUserEnvironment no If "PermitUserEnvironment" is set to "yes", is missing completely, or is commented out, this is a finding. If the required value is not set, this is a finding.

Check Text ( C-61734r952191_chk )

Verify that unattended or automatic logon via SSH is disabled with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*permituserenvironment'

PermitUserEnvironment no

If "PermitUserEnvironment" is set to "yes", is missing completely, or is commented out, this is a finding.

If the required value is not set, this is a finding.

Fix Text (F-61658r925965_fix)
Configure the RHEL 9 SSH daemon to not allow unattended or automatic logon to the system. Add or edit the following line in the "/etc/ssh/sshd_config" file: PermitUserEnvironment no Restart the SSH daemon for the setting to take effect: $ sudo systemctl restart sshd.service