What is DNS Tunneling? – GreenCloud

The Domain Name System (DNS) is one of the most important technologies used on the Internet and networking in general. This is a system that converts IP addresses into human-friendly domain names, also called Uniform Resource Locators (URLs), so that people can access websites more easily. DNS is needed because people are much better at remembering something like catchpoint.com than memorizing an IP address – especially since IPv6 addresses are 128 bits long! Since DNS has been an important technology for years, it is also closely scrutinized by hackers trying to find attack vulnerabilities. One of the most damaging types of DNS attacks is known as DNS tunneling.

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What is DNS Tunneling?

DNS tunneling is a technique used to bypass network restrictions and involves encapsulating unauthorized or non-standard data within DNS requests and responses. While it can be used for legitimate purposes, it can also be used by attackers to redirect DNS queries to their servers, giving attackers a control channel, a cloaking command, and a way to extract data.

Because DNS traffic is often allowed through firewalls and other security measures, attackers can use this protocol to hide their malicious activities. With DNS tunneling, attackers can control remote servers and applications, extract data, and bypass network restrictions, making it a dangerous attack.

How does this work?

DNS is one of the basic protocols of the Internet. It would be almost impossible to find anything on the Internet without the search services it provides. To access a website, you need to know the exact IP address of the server hosting it, which is impossible. As a result, DNS traffic is some of the most reliable traffic on the Internet. Organizations allow it to pass through the firewall (both inbound and outbound) because it is necessary for their internal employees to access external sites and for external users to find their websites.

DNS tunneling takes advantage of this fact by using DNS queries to implement a command and control channel for malware. Inbound DNS traffic may carry commands to the malware, while outbound traffic may extract sensitive information or respond to requests from the malware operator. This works because DNS is a very flexible protocol. Because websites are designed to look up domain names, there are few restrictions on the information a DNS query can contain. Since almost anything can be a domain name, these fields can be used to carry sensitive information. These requests are designed to go to DNS servers controlled by the attacker so that they can receive the requests and respond with appropriate DNS responses.

DNS tunneling attacks are easy to perform and numerous DNS tunneling toolkits are available. This allows even unspecified attackers to use this technique to leak information from an organization's network security solutions.

How do hackers use DNS tunneling?

DNS tunnels allow attackers to perform various malicious activities.

Malware installation. Attackers can use DNS tunneling to install malware on additional systems.
Collection of credentials. Once attackers gain command and control of a device, they can use keyloggers and other methods to collect user credentials that can be used to mount additional attacks or be sold on the dark web.
Exploring the network. DNS queries within an infected network can help attackers map the network, identifying systems and high-value assets.
Data extraction. Cybercriminals can use DNS tunneling to transmit data outside the network, including sensitive or confidential user data.
Control devices. Attackers can also trigger other threats, such as DDoS attacks, with the ability to control an infected device.

What are the risks of DNS tunneling?

The main risk of DNS tunneling is that it can be used to bypass network security measures. Because DNS is a necessary protocol for the internet to function, most networks allow DNS traffic to pass through without inspection. This makes DNS an ideal channel for cybercriminals to control data leaks, network infiltrations, or DNS tunneling malware.

DNS can also be used to perform tunneling attacks, where large amounts of DNS traffic are used to overwhelm the network and cause a denial of service.

In addition, DNS tunneling can be used to hide the presence of DNS-based malware on the network, making it difficult to detect and remove.

How to detect DNS tunneling?

Security teams can analyze payloads and traffic for signs of a DNS tunneling attack.

Load analysis looks at the content of DNS requests and responses. For example, unusual hostnames or significant differences between the size of the DNS query and the response may be a sign of suspicious activity. Payload analysis can also look for unusual character sets, odd data sent through DNS, infrequently used DNS record types, or repeating patterns from source IP addresses that send the most traffic.

Traffic analysis tracks information such as the number of requests made, where they originate, the history of domains, and abnormal DNS behavior. IT teams can also analyze the size of packets, as DNS tunnels typically generate larger packet sizes.

How to protect against DNS Tunnel attacks

Most companies consider the DNS protocol to be safe and secure by default. Therefore, several of them use traffic analysis to inspect DNS packets for malicious information. Instead, they prefer to focus all resources on e-mail traffic, for example.

However, ignoring DNS security best practices poses serious risks to your infrastructure. For obvious reasons, you cannot block a vital service like DNS. So here are the things you can do to protect yourself from DNS tunneling attacks.

Make sure all your internal clients' DNS queries are forwarded to the internal DNS server so you can reject any malicious domains.
Use DNS logging to quickly identify and counter potential DNS attacks.
Create a DNS firewall to detect and prevent hacker intrusions.
Use a real-time DNS security solution to identify strange DNS queries and network traffic patterns.

The result

DNS tunneling is a process where an attacker encrypts information in DNS requests and responses. By using DNS tunneling, attackers can create a communication route between a compromised system and a remote server they control. DNS Tunneling allows them to steal data, execute commands, and maintain constant control over infected systems.