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-215415r991589_rule | CCI-000366 | 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. | ||||
| STIG | Date | |||
| IBM AIX 7.x Security Technical Implementation Guide | 2024-08-16 | |||
Details
Check Text (C-215415r991589_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"