Mail relaying must be restricted.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-23952	GEN004710	SV-37514r2_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 5 Security Technical Implementation Guide	2017-01-27

Details

Check Text ( None )
None

Fix Text (F-31424r2_fix)
If the system uses sendmail, edit the sendmail.mc file and remove the "promiscuous_relay" configuration. Rebuild the sendmail.cf file from the modified sendmail.mc and restart the service. If the system does not need to receive mail from external hosts, add one or more DaemonPortOptions lines referencing system loopback addresses (such as "O DaemonPortOptions=Addr=127.0.0.1,Port=smtp,Name=MTA") and remove lines containing non-loopback addresses. Restart the service. If the system uses Postfix, edit the main.cf file and add or edit the "smtpd_client_restrictions" line to have contents "permit_mynetworks, reject" or a similarly restrictive rule. If the system does not need to receive mail from external hosts, add or edit the "inet_interfaces" line to have contents "loopback-only" or a set of loopback addresses for the system. Restart the service. If the system is using other SMTP software, consult the software's documentation for procedures to restrict mail relaying.

Fix Text (F-31424r2_fix)

If the system uses sendmail, edit the sendmail.mc file and remove the "promiscuous_relay" configuration. Rebuild the sendmail.cf file from the modified sendmail.mc and restart the service. If the system does not need to receive mail from external hosts, add one or more DaemonPortOptions lines referencing system loopback addresses (such as "O DaemonPortOptions=Addr=127.0.0.1,Port=smtp,Name=MTA") and remove lines containing non-loopback addresses. Restart the service.

If the system uses Postfix, edit the main.cf file and add or edit the "smtpd_client_restrictions" line to have contents "permit_mynetworks, reject" or a similarly restrictive rule. If the system does not need to receive mail from external hosts, add or edit the "inet_interfaces" line to have contents "loopback-only" or a set of loopback addresses for the system. Restart the service.

If the system is using other SMTP software, consult the software's documentation for procedures to restrict mail relaying.