FileUploadsFilter.php in X2Engine 4.1.7 and earlier, when running on case-insensitive file systems, allows remote attackers to bypass the upload blacklist and conduct unrestricted file upload attacks by uploading a file with an executable extension that contains uppercase letters, as demonstrated using a PHP program.
https://github.com/X2Engine/X2Engine/blob/master/CHANGELOG.md
https://cert-portal.siemens.com/productcert/pdf/ssa-234763.pdf
http://www.securityfocus.com/archive/1/533514/100/0/threaded
http://seclists.org/fulldisclosure/2014/Sep/78
http://packetstormsecurity.com/files/128353/X2Engine-4.1.7-Unrestricted-File-Upload.html