RHEL 9 must be configured to prevent unrestricted mail relaying.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257951	RHEL-09-252050	SV-257951r991589_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 9 Security Technical Implementation Guide	2024-06-04

Details

Check Text ( C-61692r925838_chk )
Verify RHEL 9 is configured to prevent unrestricted mail relaying with the following command: $ 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", and the additional entries have not been documented with the information system security officer (ISSO), this is a finding.

Check Text ( C-61692r925838_chk )

Verify RHEL 9 is configured to prevent unrestricted mail relaying with the following command:

$ 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", and the additional entries have not been documented with the information system security officer (ISSO), this is a finding.

Fix Text (F-61616r925839_fix)
Modify the postfix configuration file to restrict client connections to the local network with the following command: $ sudo postconf -e 'smtpd_client_restrictions = permit_mynetworks,reject'