WebCalendar 1.2.3, and other versions before 1.2.5, allows remote attackers to obtain sensitive information via a direct request to a .php file, which reveals the installation path in an error message, as demonstrated by ws/user_mod.php and certain other files.
http://www.openwall.com/lists/oss-security/2011/06/27/6
http://webcalendar.cvs.sourceforge.net/viewvc/webcalendar/webcalendar/ChangeLog?pathrev=REL_1_2
http://code.google.com/p/inspathx/source/browse/trunk/paths_vuln/WebCalendar-1.2.3
http://code.google.com/p/inspathx/source/browse/trunk/paths_vuln/%21_README