EasyPHPCalendar contains a flaw that may allow a remote attacker to execute arbitrary commands. The issue is due to the calendar.php script not properly sanitizing user input supplied to the "serverPath" parameter before it is used to include files. This may allow an attacker to include a file from a remote host that contains arbitrary commands which will be executed by the vulnerable script.
Upgrade to version 6.2.8 or higher, as it has been reported to fix this vulnerability. It is also possible to correct the flaw by implementing the following workaround: Set the "register_globals" PHP option to "Off".