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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-4693	GEN004680	SV-37511r1_rule	ECSC-1	Low

Description
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.

STIG	Date
Red Hat Enterprise Linux 5 Security Technical Implementation Guide	2017-03-01

Details

Check Text ( C-36171r1_chk )
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.

Check Text ( C-36171r1_chk )

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 (F-31422r1_fix)
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