delcookie.php in Professional Home Page Tools Guestbook changes the expiration date of a cookie instead of deleting the cookie's value, which makes it easier for attackers to steal the cookie and obtain the administrator's password hash after logout.

setcookie.php for the administration login in Professional Home Page Tools Guestbook records the hash of the administrator password in a cookie, which allows attackers to conduct brute force password guessing attacks after obtaining the hash.

Multiple SQL injection vulnerabilities in class.php in Professional Home Page Tools Guestbook allow remote attackers to execute arbitrary SQL commands via the (1) hidemail, (2) name, (3) mail, (4) ip, or (5) text parameters.