Rule:  

--
Sid:
2211

--
Summary:
This event is generated when an attempt is made to access guestserver.cgi on an internal web server. This may indicate an attempt to exploit a remote command execution vulnerability in Lars Ellingsen's Guestbook system.

--
Impact:
Remote execution of arbitrary code.

--
Detailed Information:
Lars Ellingsen's Guestbook system is a CGI application for web-based guestbooks. It contains a parsing vulnerability in guestserver.cgi where an attacker can place executable code within pipe characters (|) in front of an email address in the email value of a guestbook form. Because the pipe metacharacter is not properly filtered, code placed in the email value is executed with the security context of the web server.

--
Affected Systems:
Any web server running Lars Ellingsen's Guestbook system.

--
Attack Scenarios:
An attacker prepends shell commands between pipe characters to an email address in the email value of a guestbook entry. When the form data is submitted, the web server attempts to execute the commands. 

--
Ease of Attack:
Simple. Exploits exist.

--
False Positives:
If a legitimate remote user accesses guestserver.cgi on an internal web server, this rule may generate an event.

--
False Negatives:
None known.

--
Corrective Action:
Because Lars Ellingsen's guestbook system does not appear to be currently maintained, you may want to use a different guestbook application. As a workaround, you can change the 1 that appears on the line beneath <-guestbook.mailto_guest-> to 0 in the guestbook.config file.

--
Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>
Sourcefire Technical Publications Team
Jennifer Harvey <jennifer.harvey@sourcefire.com>

-- 
Additional References:

--
