The SMTP service must not have the EXPN feature active.

From VMware vRealize Operations Manager 6.x SLES Security Technical Implementation Guide

Associated with: CCI-000382

SV-99201r1_rule The SMTP service must not have the EXPN feature active.

Vulnerability discussion

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.

Check content

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

Add "noexpn" to the "PrivacyOptions" flag in the "/etc/sendmail.cf" file.

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