[Full-disclosure] D-Link DSL routers authentication bypass

2005-05-1900:00:00

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====================== SUMMARY ========================

      Title: D-Link DSL routers authentication bypass
       Date: 19 May 2005
     Author: Francesco Orro &lt;francesco.orro 4t akhela.com&gt;

    Product: DSL-502T, DSL-504T, DSL-562T, DSL-G604T
     Vendor: D-Link
 Vendor URL: http://www.dlink.com

Vendor Status: D-Link was conctacted
Affects: Tested on DSL-502T, DSL-504T, DSL-562T,
DSL-G604T with
various firmwares versions
Risk: High
Impact: Unauthorized people may gain full access to
the device

Vulnerability Description: an undocumented feature allows (in
some
cases) to bypass the authentication prompt and gain full access
to the
router, and than to the network behind it.

====================== BACKGROUND ========================

D-Link DSL routers are commonly used for internet connectivity
for home
or small office needs. (http://www.dlink.com/products/)

=============== PROBLEM DESCRIPTION ==================

The CGI /cgi-bin/firmwarecfg, when executed, checks the
existence of the
file fw_ip under /var/tmp/. If this file exists, all IP
addresses listed
inside it are given straight access to the device, without the
need for
authentication. If this file doesn't exists, the CGI creates a
new one,
putting the requesting address inside.

If the web configuration console is accessible from internet
and if
nobody have never called the CGI before (es: from a workstation
inside
the LAN), then everybody can gain access to the router,
download the
config.xml file which contains users account and passwords,
have access
to the private network, modify or alter the firmware of the
router, etc.

================ ADDITIONAL DETAILS ==================

Vulnerability was found on the following firmware versions:

V1.00B01T16.EN.20040211
V1.00B01T16.EU.20040217
V0.00B01T04.UK.20040220
V1.00B01T16.EN.20040226
V1.00B02T02.EU.20040610
V1.00B02T02.UK.20040618
V1.00B02T02.EU.20040729
V1.00B02T02.DE.20040813
V1.00B02T02.RU.20041014

Can be exploited by a simple HTTP POST with the form:

<html>
<head>Download config.xml:<title>GetConfig - Config file
download</title></head>
<body>

<form name="InputBox">
<br>http://<input Name="Host" type="text"
value="">/cgi-bin/firmwarecfg<br>
</form>
<form name="DownloadConfig" method="POST" action=""
enctype="multipart/form-data">
<input type="Submit" name="config" value="Download"
onClick="javascript:invia_richiesta();"><br>
</form>

</body>
</html>

=================== FIX INFORMATION ===================

Actually there is no solution to problem due to the fact that
it seems
an hidden feature.
The work around is to call the CGI /cgi-bin/firmwarecfg from a
known
address of the local network and/or disable web console access
from the
internet.

================ AUTHOR INFORMATION ================

Francesco Orro
Akhela S.r.l. - Operation Group
http://www.akhela.com/

EMail: francesco.orro 4t akhela.com
KeyID: 6CF46D45

=================== DISCLOSURE HISTORY =====================

2 May 2005 - First private release of this advisory;
4 May 2005 - The vendor (D-Link Mediterraneo S.r.l.) has been
informed
of the vulnerability;
5 May 2005 - The vendor replid that the problem was resolved on
firmware version V1.00B02T02.EU.20040610, but has
been
demostrated that this version is vulnerable too;
19 May 2005 - Public release of this advisory.

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