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V-253111

CAT II (Medium)

TOSS must be configured to prevent unrestricted mail relaying.

Rule ID

SV-253111r991589_rule

STIG

Tri-Lab Operating System Stack (TOSS) 4 Security Technical Implementation Guide

Version

V2R5

CCIs

CCI-000366

Discussion

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.

Check Content

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  2:3.5.8-2.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

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'