Cross-site scripting (XSS) vulnerability in PHP-Nuke 5.3.1 and earlier allows remote attackers to inject arbitrary web script or HTML via the (1) uname parameter in user.php, (2) ttitle, letter and file parameters in modules.php, (3) subject, story and storyext parameters in submit.php, (4) upload parameter in admin.php and (5) fname parameter in friend.php.

PHP-Nuke 5.2 allows remote attackers to copy and delete arbitrary files by calling case.filemanager.php with admin.php as an argument, which sets the $PHP_SELF variable and makes it appear that case.filemanager.php is being called by admin.php instead of the user.

PHP-Nuke 5.1 stores user and administrator passwords in a base-64 encoded cookie, which could allow remote attackers to gain privileges by stealing or sniffing the cookie and decoding it.