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The SMTP service must not have the EXPN feature active.


Overview

Finding ID Version Rule ID IA Controls Severity
V-240446 VRAU-SL-000625 SV-240446r671079_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.
STIG Date
VMware vRealize Automation 7.x SLES Security Technical Implementation Guide 2023-09-22

Details

Check Text ( C-43679r671077_chk )
Use the following command to check if EXPN is disabled:

# grep -v "^#" /etc/sendmail.cf |grep -i PrivacyOptions

If "noexpn" is not returned, this is a finding.
Fix Text (F-43638r671078_fix)
Add "noexpn" to the "PrivacyOptions" flag in /etc/sendmail.cf