Cross-site scripting (XSS) vulnerability in Big Blue Guestbook allows remote attackers to inject arbitrary web script or HTML via the message field in the guestbook entry submission form.
http://www.vupen.com/english/advisories/2007/1518
http://www.securityfocus.com/bid/23591
http://www.securityfocus.com/archive/1/466693/100/0/threaded