ProfilePress < 3.1.11 - Unauthenticated Cross-Site Scripting (XSS) in tabbed login/register widget

The User Registration, User Profile, Login & Membership – ProfilePress (Formerly WP User Avatar) WordPress plugin before 3.1.11's widget for tabbed login/register was not properly escaped and could be used in an XSS attack which could lead to wp-admin access. Further, the plugin in several places assigned $_POST as $_GET which meant that in some cases this could be replicated with just $_GET parameters and no need for $_POST values.