Netgear DG632 Router Authentication Bypass Vulnerability

Advisory Content :

Product Name: Netgear DG632 Router
Vendor: http://www.netgear.com
Date: 15 June, 2009
Author: tom (at) tomneaves.co (dot) uk [email concealed] <tom (at)
tomneaves.co (dot) uk [email concealed]>
Original URL:
http://www.tomneaves.co.uk/Netgear_DG632_Authentication_Bypass.txt
Discovered: 18 November, 2006
Disclosed: 15 June, 2009

I. DESCRIPTION

The Netgear DG632 router has a web interface which runs on port 80. This
allows an admin to login and administer the device's settings.
Authentication ofm this web interface is handled by a script called "webcm"
residing in "/cgi-bin/" which redirects to the relevant pages depending on
successful user authentication.
Vulnerabilities in this interface enable an attacker to access files and
data without authentication.

II. DETAILS

The "webcm" script handles user authentication and attempts to load
"indextop.htm" (via javascript below). The "indextop.htm" page requires
authentication (HTTP Basic Authorization).

---

<script language="javascript" type="text/javascript">
function loadnext() {
//document.forms[0].target.value="top";
document.forms[0].submit();
//top.location.href="../cgi-bin/webcm?nextpage=../html/indextop.htm";
}</script></head>
<body bgcolor="#ffffff" onload="loadnext()" >

Loading file ...
<form method="POST" action="../cgi-bin/webcm" id="uiPostForm">
<input type="hidden" name="nextpage" value="../html/indextop.htm"
id="uiGetNext">
</form>

---

If a valid password to the default "admin" user is supplied, the script
then continues to load
the "indextop.htm" page and continues to load the other frames based on a
hidden field. If user
authentication is unsuccessful, the user is returned back to
"../cgi-bin/webcm". It is possible
to bypass the "webcm" script and access specific files directly without the
need for authentication.

Normal use:
http://TARGET_IP/cgi-bin/webcm?nextpage=../html/stattbl.htm

This would ask for the user to authenticate and would refuse access to this
file if authentication
details were not known. All the script is doing is making sure
authentication is forced upon the user. The same "stattbl.htm" file can be
accessed without having to provide any authentication using the following
URL:

http://TARGET_IP/html/stattbl.htm

Another example:
http://192.168.0.1/cgi-bin/webcm?nextpage=../html/modemmenu.htm
(returns 401 - Forbidden)

Bypassing the "webcm" script:
http://192.168.0.1/html/modemmenu.htm
(returns 200 - OK)

In the example above (modemmenu.htm), the full source can be viewed which
discloses further directories and files within the javascript of the page.
A sample of files disclosed within modemmenu.htm and available to download
are:

/html/onload.htm
/html/form.css
/gateway/commands/saveconfig.html
/html/utility.js (full source)

There are many other files that are accessible by calling them directly
instead of going via the "webcm" script,the above are just a sample. In
addition, it is possible to specify paths to
the "webcm" script as shown below:

http://TARGET_IP/cgi-bin/webcm?nextpage=../../

This allows an attacker to enumerate what files and directories exist
within the www root directory and beyondby using 200, 403 and 404 errors as
a guide.

Affected Versions: Firmware V3.4.0_ap (others unknown)

III. VENDOR RESPONSE

12 June, 2009 - Contacted vendor.
15 June, 2009 - Vendor responded. Stated the DG632 is an end of life
product and is no longer supported in a production and development sense,
as such, there will
be no further firmware releases to resolve this issue.

IV. CREDIT

Discovered by Tom Neaves

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Netgear DG632 Router Authentication Bypass Vulnerability