Trustwave's SpiderLabs Security Advisory TWSL2011-002: Vulnerabilities in Comcast DOCSIS 3.0 Business Gateways (D3G-CCR) 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 ## d3g-csrf-poc-1.htm
## d3g-csrf-poc-2.htm
## d3g-csrf-poc-3.htm
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. ## #!/bin/bash start=1267604160 end=1267605960 for (( i=$start; i<=$end; i++)) do if [ `curl -sb userid=$i | 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 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 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 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. 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.