What is DNS Tunneling and How Can It be Prevented? [Explained]

Domain Name System or in short, DNS, is an application layer protocol that translates domain names or URLs to IP addresses. Since humans are comfortable with reading websites as systoolsms.com rather than 128-bit long IPv6 addresses, DNS has been an essential technology for years. DNS traffic is some of the most trusted traffic on the Internet. This traffic is often able to pass through firewalls and other systems without much scrutiny. By taking advantage of the same, hackers are infecting this through DNS tunneling.

What is DNS Tunneling? 

DNS tunneling is a type of cyber attack through which hackers embed malicious programs in the form of DNS requests.

There are various DNS tunneling attack examples.

Example 1: Command and Control (C2) –The malware uses DNS requests and replies to establish a C2 channel with its handler rather than using them to carry out genuine IP address lookups. This particular type of cyber attack involves abuse of the underlying DNS protocol and could create a bigger problem for an organization.

Example 2: Data Exfiltration – Adversaries gradually exfiltrate data by encoding it into a number of DNS host searches over time.

Example 3: Wi-Fi Abuse and Policy Bypass – By taking advantage of systems that permit IP traffic out, an attacker builds a full IPv4 tunnel. They are able to do this to get past security and IT policy firewalls as well as paid WiFi gates to access an internal network.

How Does DNS Tunneling Work? – Know the Detailed Approach

Hackers follow a structured plan and popular DNS Tunneling Toolkits to carry out this cyber attack. Let’s understand with the help of the below figure.

1. The hacker uses a domain, for example, ‘test.com’, and configures the domain’s name server to his own server.
2. Then, the attacker delegates a subdomain such as ‘code.test.com’ and sets up his machine as the subdomain’s legislative DNS server.
3. After that, any DNS request made by the target to “{data}.code.test.com” will redirect to the attacker’s machine.

A two-way communication channel is created by the attacker and this passage can be used to exfiltrate data from the victim’s system or for other malevolent purposes. 

Understand Attackers’ Objectives Behind Executing DNS Tunneling Attack

The thing to note here is that hackers use this attack as a gateway to carry out other malicious acts. That means their end goal is not to perform this type of attack directly, rather their intention is to use DNS tunneling as a medium to complete other malicious activities.

Experts see this type of attack as a hacking tool or strategy that is used by hackers to launch other malevolent acts. Such as,

1. Malware Installation: Once the threat actors take control of the victim’s environment, they install viruses on computers within their network. From sending infected emails to getting a user to insert a compromised USB drive, the adversaries will try everything to fulfill their intention.
2. Gather Login Credentials: Attackers collect user IDs and passwords using the compromised system and further send these credentials via the DNS tunnel they have created.
3. Network Imprinting: Hackers can build a system map through DNS queries within an infected network. Through this map, they identify what systems are being used and can potentially help them create future vulnerabilities. 
4. Control Communication: Sophisticated hackers perform regular check-ins with their host server through DNS tunneling toolkits. And, their main aim is to maintain communication, receive additional commands, and remain in the victim’s environment for an extended period of time.

Above are some of the most common types of attacks that are associated with DNS tunneling attacks. Moreover, advanced hackers use DNS tunneling toolkits to successfully exploit a connection or put malware in place.

Adverse Effects of DNS Tunneling on Users

DNS tunneling is a cyber attack that leads to unfavorable events.  

• Threat actors release private data through DNS. Although it isn’t the most effective method for retrieving data from a target’s PC due to the additional overhead and encoding, it can be used. 
• Through the C2 model, hackers use the DNS protocol to send simple commands to remote access the environment.
• On the DNS query-response protocol, the IP stack has been implemented by some tools. Data transfer would be comparatively easy for hackers if conventional communications programs like FTP, Netcat, and SSH were used. 

Common DNS Tunneling Detection Techniques

Detecting stealth mode attacks is not so easy, especially DNS tunneling. However, there are several ways through which this type of attack can be identified.

• Payload Analysis: Keeping an eye on the ratio of the bytes used in the source field to the bytes used in the destination field can help detect suspicious activity. Plus, paying close attention to the peculiar-looking hostnames, a DNS record type that is not utilized all that frequently, and unordinary character sets can be of great help. 
• Traffic Analysis: Look for atypical behavior occurring in your network and analyze all types of traffic coming in and out of the network. Traffic analysis uses information such as the number of requests, geographic locations, and domain history which helps in detecting the security loophole in the domain name system.

Preventive Measures for Avoid DNS Tunneling Attacks

As a defender, it’s important to keep in mind that to successfully carry out this attack, the hacker needs the right tools and an infected device inside the victim’s network. So, to protect your organization’s network, first of all, you should have a robust plan and some key mechanisms in place.

• Updated Anti-virus Software: A good antivirus or antimalware program acts as an armor against possible security threats. So, it’s absolutely essential for any corporate network to have such malware protection software. 
• Advanced Network Traffic Monitoring: A 360-degree network monitoring looks for all types of potentially malicious traffic present in the network. The Network Operations Center (NOC) will fulfill the requirement of identifying any malevolent activity in the network at the early stage and prevent it from causing further damage.
• Cybersecurity Training: Any computer system’s vulnerable spot is the collection of human behaviors used to access the network. By educating your staff to refrain from opening suspicious emails, clicking on unauthorized links, and performing other acts that can encourage infection, it’s possible to protect organizations’ systems from DNS tunneling attacks.

Final Words

In the internet world, DNS plays an important role for all kinds of businesses. However, hackers are exploiting this platform through DNS tunneling attacks, and mitigating such attacks is essential for running business operations smoothly. That’s why here we covered the detection and prevention techniques for your reference.

FAQs

Q- Why DNS tunneling attacks are a matter of concern?

Because DNS communication is often let through firewalls and other security measures, DNS tunneling attacks can be difficult to spot. As a result, they represent an appealing way for attackers to sustain persistence and exfiltrate data covertly.

Q- What types of data are capable of tunneling through DNS?

Text-based data, binary files, malware payloads, and command and control instructions for compromised computers are just a few of the several sorts of data that attackers can tunnel over DNS.

Q- Are there any appropriate applications for DNS tunneling?

Yes, there are legal applications for DNS tunneling, such as encrypting DNS communication with DNS over HTTPS (DoH) or DNS over TLS (DoT) to improve security and privacy. However, these acceptable uses are frequently well-researched and standardized.

Q- Are there any tools present for DNS tunneling attack detection?

Yes, there are some common tools and techniques present through which one can detect this type of attack. Refer to the below points.

• Detecting DNS anomalies involves monitoring DNS traffic for odd trends or sudden increases in volume.
• Analysing DNS queries and responses for lengthy or odd subdomains is known as DNS query/response analysis.
• Using DNS managed security services to identify and stop malicious DNS traffic is one way to implement DNS security solutions.
• Analyzing network traffic involves using tools for network monitoring to spot odd DNS behavior.

Q- How to protect an organization’s networks from DNS tunneling?

In order to stop such attacks, companies can:

• Put in place appropriate DNS security measures.
• Keep an eye on DNS traffic and filter out any irregularities.
• Make use of DNS security tools.
• Update DNS configurations and software on a regular basis.
• Employ threat intelligence feeds based on DNS to find known dangerous domains.