phpMyAgenda contains a flaw that may allow a remote attacker to execute arbitrary commands. The issue is due to agenda.php3 not properly sanitizing user input supplied to the 'rootagenda' variable. 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 3.1 beta 1 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.