SMTP service must not have the EXPN or VRFY features active on AIX systems.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-215415	AIX7-00-003117	SV-215415r508663_rule		Medium

Description
The SMTP EXPN function allows an attacker to determine if an account exists on a system, providing significant assistance to a brute force attack on user accounts. EXPN may also provide additional information concerning users on the system, such as the full names of account owners. The VRFY (Verify) command allows an attacker to determine if an account exists on a system, providing significant assistance to a brute force attack on user accounts. VRFY may provide additional information about users on the system, such as the full names of account owners.

Description

The SMTP EXPN function allows an attacker to determine if an account exists on a system, providing significant assistance to a brute force attack on user accounts. EXPN may also provide additional information concerning users on the system, such as the full names of account owners. The VRFY (Verify) command allows an attacker to determine if an account exists on a system, providing significant assistance to a brute force attack on user accounts. VRFY may provide additional information about users on the system, such as the full names of account owners.

STIG	Date
IBM AIX 7.x Security Technical Implementation Guide	2020-09-11

Details

Check Text ( C-16613r294696_chk )
Check the "PrivacyOptions" parameter in "/etc/mail/sendmail.cf": # grep -v "^#" /etc/mail/sendmail.cf \|grep -i privacyoptions The above command should yield the following output: O PrivacyOptions=goaway The "O PrivacyOptions" should have the "goaway" option (covering both noexpn and novrfy). If the "O PrivacyOptions" value does not contain "goaway", this is a finding.

Fix Text (F-16611r294697_fix)
Edit the "sendmail.cf" file and add or edit the following line: O PrivacyOptions=goaway Restart the "Sendmail" service: # startsrc -s sendmail -a "-bd -q30m"