Netgear Wireless Cable Modem Gateway - Authentication Bypass / Cross-Site Request Forgery








Sense of Security - Security Advisory - SOS-11-011

Release Date.                  20-Sep-2011
Last Update.                   -
Vendor Notification Date.      22-Mar-2011
Product.                       NETGEAR Wireless Cable Modem Gateway
Affected versions.             Hardware 1.03, 
                               Software V3.9.26 R14 verified,
                               possibly others
Severity Rating.               High
Impact.                        Authentication bypass,
                               Cross Site Request Forgery
Attack Vector.                 Remote without authentication
Solution Status.               Upgrade to R15 (by contacting NETGEAR)
CVE reference.                 Not yet assigned

The NETGEAR Wireless Cable Modem Gateway CG814WG is supplied by ISP's 
as customer premises equipment within Australia and abroad. It is a 
centrally managed ISP solution whereby each ISP's devices run a 
customised firmware and configuration changes and updates can be pushed 
out as required. 

Basic authentication is used as the primary and only authentication 
mechanism for the administrator interface on the device. The basic 
authentication can be bypassed by sending a valid POST request to the 
device without sending any authentication header. The response from the 
device sends the user to another page that requests basic 
authentication, however at this point the request has already been 

An example of attacks using the basic authentication bypass may include 
changing the admin password or enabling the remote admin interface 
(Internet facing). 

Additionally, due to the lack of CSRF protection in the web application, 
the bypass attack can be coupled with CSRF to have a victim enable the 
remote admin interface to the Internet, where an attacker can then use 
the bypass attack again across the remote admin interface to reset the 
admin password and access the device. This attack is possible when 
targeting a victim that is behind the NETGEAR device on the same segment 
as the web administrator interface whom has browsed to a malicious site 
containing the CSRF attack. 

NETGEAR was notified of this vulnerability on 22 March 2011, but we 
never received a response or acknowledgement of the issue or fix. Sense 
of Security notified local ISP's and it was escalated by a local ISP 
who worked with NETGEAR to develop and test an update. Sense of Security 
was never provided an opportunity to validate the fixes in the latest 
firmware version. Given the severity of the issue it would be prudent 
for NETGEAR to notify and supply an update to all of its customers. 

Proof of Concept. 
By embedding the below HTML in a website and having a 
victim browse to the website the remote management interface to the 
Internet would be enabled. An attacker could then use one of the 
hardcoded passwords for the device to access it, or use a basic 
authentication bypass to change the admin password. Alternatively, the 
attacker could conduct a CSRF attack that implements two POST requests 
to have the remote admin interface enabled, and the admin password 

The example here is a basic proof of concept, more complex examples 
which include JavaScript redirects to mask the basic authentication 
pop-up would be more stealthy. 

<body onLoad=javascript:document.form.submit()>
<form action=""
method="POST" name="form">
<input type="hidden" name="NetgearRmEnable" value="0x01">
<input type="hidden" name="NetgearRmPortNumber" value="1337">
<input type="hidden" name="NetgearUserLevel" value="1">

Ask your ISP to obtain the latest firmware from NETGEAR and deploy it
to your device.

Discovered by.
Sense of Security Labs.

About us.
Sense of Security is a leading provider of information
security and risk management solutions. Our team has expert
skills in assessment and assurance, strategy and architecture,
and deployment through to ongoing management. We are
Australia's premier application penetration testing firm and
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Level 8, 66 King St
Sydney NSW 2000

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