Open DNS resolver vulnerability alert

Last updated: April 11, 2019

You may have recently received a letter and/or email from Virgin Media explaining that we have been notified that a device on your network has a vulnerability known as an Open DNS Resolver. If you have received such a communication from us, read the advice given on this page to help resolve the issue. Note: This article is intended to provide advice. Virgin Media is not responsible for any issues encountered in the course of resolving the issue and is not able to provide any technical support for such problems.

Overview

The Domain Name System (DNS) is a system used by computers to convert domain names to an IP address on the Internet. A DNS server is a system that accepts requests from other computer systems to convert domains to IP addresses.

An open recursive DNS Resolver is a DNS server that has been opened up to answer DNS queries from any computer system on the Internet. If configured incorrectly, these servers can be exploited to unwittingly participate in malicious activities.

What has happened?

We work with a number of not-for-profit organisations across the banking industry and security sectors that collate information on devices across the Internet that appear to be compromised or misconfigured. This means that your compromised or misconfigured device is publicly accessible on the Internet, and therefore the scanning that is performed by these organisations is not within your private network.

We suspect a device connected to your home network may have an open DNS resolver vulnerability.

For more information on these reports please visit dnsscan.shadowserver.org*

If the settings are left open they can be exploited to unwittingly participate in malicious activities, for example a Distributed Denial of Service (DDoS) attack.

It is therefore important that you follow the advice in this article. **

 

The easiest way to deal with an Open DNS resolver is to configure your firewall to block port 53 to prevent DNS queries from outside your home network.

If you have a specific need to have a DNS resolver that answers to queries from the Internet, please ensure your server is configured to only accept traffic from IP addresses that need to use the server.

Hub 3.0

To close the vulnerable port on the Virgin Media Hub 3.0:

  • Access your Hub's configuration page - default web address: 192.168.0.1
  • Login with your username and password, default will be shown on the Hub itself
  • Select Security on the left side of the page
  • Select the Port Forwarding option
  • Remove any rules that will keep port 53 open
  • Select the Port Triggering option
  • Remove any rules that will keep port 53 open

Virgin Media Super Hub

To close the vulnerable port on the Super Hub 1 or 2’s firewall:

  • Access your Hub's configuration page - default web address: 192.168.0.1
  • Login with your username and password, default will be shown on the Hub itself
  • Select Advanced Settings and accept the prompt
  • Scroll down to the Security section
  • Select the Port Forwarding option
  • Tick the Delete box next to any rules that will keep port 53 open
  • Click the Apply option
  • Select the Port Triggering option
  • Tick the Delete box next to any rules that will keep port 53 open
  • Click the Apply option

3rd party routers

If you use a 3rd party router in conjunction with the Virgin Media Super Hub or Hub 3.0, your router's firewall will need to be configured to ensure port 53 is not accessible outside of your local network - this can be performed by blocking the port or removing any Port Forwarding rules for port 53. In order to identify how to do this with your particular router, refer to the documentation for your device or refer to the manufacturer's website.

It is important to check all your devices sit behind a firewall. In most cases your firewall is configured as a part of your router, this is the case with the Virgin Media Super Hub and Hub 3.0. If you have specifically disabled the Firewall in your router, it is crucial that you configure your devices to sit behind a firewall that is blocking port 53. If this does not apply to you, please proceed to the next step.

Modem Mode - If you are using your Virgin Media Super Hub or Hub 3.0 in Modem Only mode, it is essential that you are using a firewall on any device or router that is plugged directly into the Hub. When in Modem Only mode, your Hub does not operate with a firewall. If this does not apply to you, please proceed to the next step.

DMZ - Most firewalls, including the one provided with the Virgin Media Super Hub and Hub 3.0 include a DMZ option. This feature allows for a device using a specific local IP address on your home network (e.g. 192.168.0.2) to bypass your Firewall settings. This is occasionally necessary if you are using a device that has its own firewall configured.

If you have a device configured in your firewall's DMZ that does not use its own firewall, it is crucial that you disable this option immediately. Computers operating without a firewall are extremely vulnerable to attack as all ports are essentially exposed to the wider Internet.


Where can I find further information and advice?

If you’d like further advice then our forum community will be happy to help. Just visit virginmedia.com/community and join the conversation on our Security Matters board.

You can find general security advice and articles on other vulnerabilities by checking Security Hub at virginmedia.com/securityhub

* links to external sites are provided as a courtesy and virgin media is not responsible for the content of these sites or any issues encountered as a result of  applying information from these sites. Virgin media are not able to provide any technical support for such problems.

** These fixes are provided as a courtesy and we are not responsible for any problems encountered whilst applying these steps and we are not able to provide any technical support for such problems.

 


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