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Free examples of this are Cloudfare (just check you’re not using 1.1.1.1 in your network…), or OpenDNS (free for home use).
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The easiest way to implement this is by using a public DNS resolver that provides a layer of security. This is done by analyzing the DNS queries from your network and if one of them is for a known bad domain, it is dropped. There’s many approaches you can follow to block DNS tunneling, which one to choose will depend on your current deployment: Now this is the bit where I’ve struggled to find more information on. Blocking DNS tunneling on your network (with an example!): The 6 Steps in DNS tunneling (simplified):Ĥ. This is the defined nameserver which will ultimately receive the DNS requests. So DNS servers will redirect its requests to a defined server of our own. Will launch DNS requests with data in them to a domain. Nameserver record): Maps a domain name to a list of DNS servers, in case our website is hosted in multiple servers.Į →,
- A Record: Maps a domain name to an IP address.
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That helps us remember many websites, same as we can remember many people’s names.įor those who know what DNS is I would suggest looking here for a quick refresh on DNS, but in short what you need to know is: There’s even at least one VPN over DNS provider (warning: the design of the website is hideous, making me doubt on the legitimacy of it).Īs a pentester all this is great, as a network admin not so much.įor those who know nothing about DNS but still made it here, I think you deserve a very brief explanation on what DNS does: DNS is like a phonebook for the internet, it translates URLs (human-friendly language, the person’s name), into an IP address (machine-friendly language, the phone number). To make it even more worrying, there’s a large amount of easy to use DNS tunneling tools out there. Possibilities here are endless: Data exfiltration, setting up another penetration testing tool… you name it. Like, back to 1998 slow.Īnother more dangerous use of DNS tunneling would be bypassing network security devices (Firewalls, DLP appliances…) to set up a direct and unmonitored communications channel on an organisation’s network. This sounds fun but reality is, browsing anything on DNS tunneling is slow. On those shared internet hotspots HTTP traffic is blocked until a username/password is provided, however DNS traffic is generally still allowed in the background: we can encode our HTTP traffic over DNS and voilà, we have internet access. Hotels generally provide an access code if you ask… but we all have introvert days.