admin.php in PHP-Nuke 5.2 and earlier, except 5.0RC1, does not check login credentials for upload operations, which allows remote attackers to copy and upload arbitrary files and read the PHP-Nuke configuration file by directly calling admin.php with an upload parameter and specifying the file to copy.
https://exchange.xforce.ibmcloud.com/vulnerabilities/7170
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-1013
http://www.securityfocus.com/bid/3361
http://sourceforge.net/forum/forum.php?forum_id=113892
http://archives.neohapsis.com/archives/bugtraq/2001-09/0203.html