Session fixation vulnerability in fileupload.php in PivotX before 2.3.11 allows remote attackers to hijack web sessions via the sess parameter.
http://www.securityfocus.com/bid/75577
http://www.securityfocus.com/archive/1/535860/100/0/threaded
http://blog.pivotx.net/archive/2015/06/21/pivotx-2311-released