Title

SMTP service banner response reveals configuration details. (Cat II impact)

Discussion

Automated connection responses occur as a result of FTP or Telnet connections, when connecting to those services. They report a successful connection by greeting the connecting client, stating the name, release level, and (often) additional information regarding the responding product. While useful to the connecting client, connection responses can also be used by a third party to determine operating system (OS) or product release levels on the target server. The result can include disclosure of configuration information to third parties, paving the way for possible future attacks. For example, when querying the SMTP service on port 25, the default response looks similar to this one: 220 exchange.mydomain.org Microsoft ESMTP MAIL Service, Version: 6.0.3790.211 ready at Wed, 2 Feb 2005 23:40:00 -0500 Changing the response to hide local configuration details reduces the attack profile of the target.

Check Content

For each SMTP server (1 thru x) issue the following command: CSCRIPT ADSUTIL.VBS get smtpsvc/x/connectresponse (Where x is the relative number of SMTP virtual server identified on the machine). Criteria: If a modified response is returned, for example: ESMTP …. (Time and date) message is returned, this is not a finding.

Fix Text

Change the banner response text as follows: CSCRIPT ADSUTIL.VBS get esmtpsvc/x/connectresponse "ESMTP" Then, recycle the SMTP service by issuing the commands: NET STOP SMTPSVC, followed by NET START SMTPSVC. Alternately, the value can be changed by accessing the Exchange user interface as follows: Exchange System Manager >> Default SMTP Virtual Server >> Delivery >> Properties >>Advanced Change the value to “ESMTP”. Recycle the SMTP service: NET STOP SMTPSVC, followed by NET START SMTPSVC.

Additional Identifiers

Rule ID: SV-21318r1_rule

Vulnerability ID: V-18792

Group Title:

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.