The SMTP service must not have the VRFY feature active.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-4693	GEN004680	SV-39171r1_rule	ECSC-1	Low

Description
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
AIX 6.1 SECURITY TECHNICAL IMPLEMENTATION GUIDE	2015-06-16

Details

Check Text ( C-38150r1_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 Locate the sendmail.cf configuration file. Procedure: # find / -name sendmail.cf -print # grep -v "^#" \|grep -i vrfy Ensure 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-38150r1_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

Locate the sendmail.cf configuration file.
Procedure:
# find / -name sendmail.cf -print # grep -v "^#" |grep -i vrfy

Ensure 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-33425r1_fix)
If you are running Sendmail, add the line Opnovrfy to your Sendmail configuration file, usually located in /etc/sendmail.cf. For other mail servers, contact the vendor for information on how to disable the verify command. Newer versions of Sendmail are available at http://www.sendmail.org or from ftp://ftp.cs.berkeley.edu/ucb/sendmail.