CMS Made Simple Authenticated RCE via object injection

An issue was discovered in CMS Made Simple 2.2.8.
In the module DesignManager (in the files action.admin_bulk_css.php
and action.admin_bulk_template.php), with an unprivileged user
with Designer permission, it is possible to reach an unserialize
call with a crafted value in the m1_allparms parameter,
and achieve object injection.

This module has been successfully tested on CMS Made Simple versions
2.2.6, 2.2.7, 2.2.8, 2.2.9 and 2.2.9.1.