The Multiple Roles per User plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the 'mrpu_add_multiple_roles_ui' and 'mrpu_save_multiple_user_roles' functions in all versions up to, and including, 1.0. This makes it possible for authenticated attackers, granted the 'edit_users' capability, to edit any user's role, including promoting users to Administrator and demoting Administrators to lower-privileged roles.