Michael Salzer Guestbox 0.6, and other versions before 0.8, allows remote attackers to post an admin comment to a guestbook entry via a certain modified form, possibly related to the nummer parameter.

Multiple cross-site scripting (XSS) vulnerabilities in Michael Salzer Guestbox 0.6, and other versions before 0.8, allow remote attackers to inject arbitrary web script or HTML via (1) HTML tags that follow a "http://" string, which bypasses a regular expression check, and (2) other unspecified attack vectors.

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.