DNS Tunneling: How it Works, Detection and Prevention

Ayush Parti
September 19, 2022

As digital exploits continue to evolve, cyber attackers are finding new and innovative ways to gain access to systems and data. One such exploit that has been on the rise in recent years is DNS tunnelling since it is difficult to detect.

DNS tunneling is a strategy that uses domain name servers (DNS) to encode the information of different programs or protocols. This can include anything from sensitive data to control commands that can be used to take over a system. DNS tunneling is often used in conjunction with other exploits, such as malware, in order to gain greater access and control over a target system.

In other words, DNS tunneling is a way of exploiting the DNS protocol to "tunnel" malware programs. It routes a DNS request to the attacker's server– providing them with an exfiltration path.

There are a number of reasons why DNS tunneling can be problematic for businesses and organizations. First, it can be difficult to detect and stop since the traffic appears to be normal DNS traffic. Additionally, it can be used to bypass security measures and access sensitive data or systems undetected. Lastly, DNS tunnelling can be used to install malware or other malicious software on a target system, which can cause significant damage or even loss of data.

In this blog, we will be taking a deep dive into DNS tunnelling, how it works, and what you can do to prevent it.

What is a DNS (Domain Name System)?

A DNS is a bit like a phone book for the internet. When you type in a web address like www.example.com, your DNS server translates that into an IP address like 192.0.2.1. DNS servers know the addresses of all the websites on the internet and can direct your computer to the right one when you want to view a particular website. DNS servers are run by ISPs (internet service providers) and organizations like Google.

You can also run your own DNS server, but most people don't need to do this. DNS servers are important because they make it possible for you to access websites using easy-to-remember names instead of hard-to-remember IP addresses. DNS servers are also used to help direct email to its proper destination. For example, when you send an email to someone at example.com, your DNS server will look up the MX (mail exchange) record for example.com and use that to determine where to send the email message.


How DNS Tunneling Works 

DNS tunnelling works by encapsulating data traffic within DNS queries and responses. The data is first encrypted and then encapsulated within a DNS query. The DNS query is then sent to a DNS server, which resolves the query and returns the results to the client. 

This technique can be used to bypass firewall restrictions and gain access to restricted networks. By encapsulating the data traffic within DNS queries and responses, the traffic appears to be legitimate DNS traffic and is not blocked by firewalls. 

DNS tunnelling can also be used for malicious purposes, such as data exfiltration or botnet communication. adversaries can use DNS tunnelling to transfer sensitive data out of a network without being detected. They can also use it to communicate with botnets or other malicious infrastructure without being detected by security systems. 

What are the Threats Posed by DNS Tunneling?

1. DNS tunneling can be used to bypass firewalls.

DNS tunneling involves using the DNS protocol to send data through a network that would otherwise be blocked by a firewall. This can pose a serious security threat, as it allows attackers to bypass security measures and gain access to sensitive information.

2. DNS tunneling can be used to exfiltrate data.

DNS tunneling can also be used to exfiltrate data from a network. This is often done by encoding data into DNS queries and responses, and then sending them through a DNS server that is not being monitored by the organization's security team. This can allow attackers to steal sensitive information without being detected.

3. DNS tunneling can be used to distribute malware.

DNS tunneling can also be used to distribute malware. This is often done by embedding malicious code into DNS queries and responses, and then sending them through a DNS server that is not being monitored by the organization's security team. This can allow attackers to infect computers on the network with malware without being detected.

4. DNS tunnelling can be used to launch DDoS attacks.

DNS tunnelling can also be used to launch attacks against organizations or individuals. This is often done by using a DNS server to resolve queries for domain names that are actually IP addresses of devices on the target network. This can allow attackers to launch attacks against these devices without being detected.

5. DNS tunneling can be used for reconnaissance.

DNS tunneling can also be used for reconnaissance purposes. This is often done by resolving domain names that are actually IP addresses of devices on the target network. This can allow attackers to gather information about the network without being detected

How to Identify a DNS Tunneling Attack Taking Place

Instead of using DNS replies to conduct an IP address search, a malicious entity can hijack the DNS to include a contr

There are a few indicators that may suggest that a DNS tunneling attack is taking place, including:

  • Increased DNS traffic, particularly DNS queries that are not typically seen
  • DNS requests that resolve to unusual IP addresses
  • DNS requests that use non-standard ports
  • DNS requests that use unusual record types

How to Prevent DNS Tunneling?

There are several ways to prevent DNS tunneling, including:

- Restricting access to DNS servers: Only allowing trusted users to access DNS servers can help to prevent unauthorized DNS queries from being made.

- Monitoring DNS traffic: Monitoring DNS traffic for unusual activity can help to identify attempts at DNS tunneling.

- Blocking suspicious DNS queries: Blocking suspicious DNS queries can help to prevent data from being exfiltrated via DNS tunneling.

Rid yourself from DNS Tunneling Vulnerabilities with Heyhack Protect

DNS tunneling is a powerful tool that can be used for both legitimate and malicious purposes. Software engineers should be aware of how this technique works and how it can be used to their advantage.

Heyhack Protect provides a robust solution for detecting DNS tunneling so you can take proactive measures to protect your web applications! To learn more, get in touch.

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