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: --
