The SMTP service must not have the Verify (VRFY) feature active.

From Oracle Linux 5 Security Technical Implementation Guide

Associated with: CCI-000366

SV-62859r1_rule The SMTP service must not have the Verify (VRFY) feature active.

Vulnerability discussion

The VRFY 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.

Check content

Determine if VRFY is disabled. Procedure: # telnet localhost 25 vrfy root If the command does not return a 500 error code of "command unrecognized", this is a finding. or: # grep -v "^#" /etc/mail/sendmail.cf |grep -i vrfy Verify the VRFY command is disabled with an entry in the sendmail.cf file. The entry could be any one of "Opnovrfy", "novrfy", or "goaway", which could also have other options included, such as "noexpn". The "goaway" argument encompasses many things, such as "novrfy" and "noexpn". If no setting to disable VRFY is found, this is a finding.

Fix text

Add the "novrfy" flag to your sendmail in /etc/mail/sendmail.cf. Procedure: Edit the definition of "confPRIVACY_FLAGS" in /etc/mail/sendmail.mc to include "novrfy". Rebuild the sendmail.cf file with: # make -C /etc/mail Restart the sendmail service. # service sendmail restart

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