RHEL 8 must be configured to prevent unrestricted mail relaying.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-230550	RHEL-08-040290	SV-230550r627750_rule		Medium

Description
If unrestricted mail relaying is permitted, unauthorized senders could use this host as a mail relay for the purpose of sending spam or other unauthorized activity.

STIG	Date
Red Hat Enterprise Linux 8 Security Technical Implementation Guide	2021-06-14

Details

Check Text ( C-33219r568396_chk )
Verify the system is configured to prevent unrestricted mail relaying. Determine if "postfix" is installed with the following commands: $ sudo yum list installed postfix postfix.x86_64 2:3.3.1-9.el8 If postfix is not installed, this is Not Applicable. If postfix is installed, determine if it is configured to reject connections from unknown or untrusted networks with the following command: $ sudo postconf -n smtpd_client_restrictions smtpd_client_restrictions = permit_mynetworks, reject If the "smtpd_client_restrictions" parameter contains any entries other than "permit_mynetworks" and "reject", this is a finding.

Check Text ( C-33219r568396_chk )

Verify the system is configured to prevent unrestricted mail relaying.

Determine if "postfix" is installed with the following commands:

$ sudo yum list installed postfix

postfix.x86_64 2:3.3.1-9.el8

If postfix is not installed, this is Not Applicable.

If postfix is installed, determine if it is configured to reject connections from unknown or untrusted networks with the following command:

$ sudo postconf -n smtpd_client_restrictions

smtpd_client_restrictions = permit_mynetworks, reject

If the "smtpd_client_restrictions" parameter contains any entries other than "permit_mynetworks" and "reject", this is a finding.

Fix Text (F-33194r568397_fix)
If "postfix" is installed, modify the "/etc/postfix/main.cf" file to restrict client connections to the local network with the following command: $ sudo postconf -e 'smtpd_client_restrictions = permit_mynetworks,reject'