Michael Salzer Guestbox 0.6, and other versions before 0.8, allows remote attackers to obtain the source IP addresses of guestbook entries via a direct request to /gb/gblog.
https://exchange.xforce.ibmcloud.com/vulnerabilities/24799
http://www.vupen.com/english/advisories/2006/0675
http://www.securityfocus.com/archive/1/426663/100/0/threaded
http://www.securityfocus.com/archive/1/425495/100/0/threaded