Multiple SQL injection vulnerabilities in ClassSystem 2.3 allow remote attackers to execute arbitrary SQL commands via the teacher_id parameter in (1) class/HomepageMain.php and (2) class/HomepageTop.php, and (3) the message_id parameter in class/MessageReply.php.
https://exchange.xforce.ibmcloud.com/vulnerabilities/42650
http://www.vupen.com/english/advisories/2008/1664
http://www.securityfocus.com/archive/1/492583/100/0/threaded