It indicates a possible exploit of a PHP remote file inclusion vulnerability in ACal.
This flaw is due to an input validation error in the "embed/day.php" script that does not validate the "path" parameter.
ACal ACal 2.2.6
ACal ACal 2.2.5
ACal ACal 2.2.4
The execution of arbitrary PHP code on the system.
Currently we are not aware of any official supplied fix for this issue.