DNS Tunneling: The Risks and Real Examples

The Domain Name System (DNS) is a crucial technology used in networking and on the internet. Its main function is to convert IP addresses to easy-to-remember domain names or Uniform Resource Locators (URLs) so that people can access websites with ease. This technology is important because humans can easily remember domain names like catchpoint.com compared to lengthy IP addresses, especially since IPv6 addresses are 128 bits long. 

DNS has been in use for many years and is, therefore, closely scrutinized by hackers who are always searching for vulnerabilities to exploit. DNS tunneling is one of the most harmful forms of DNS attacks and can cause significant damage.

What is DNS Tunneling? 

DNS Tunneling is a technique used by cybercriminals and hackers to bypass network security measures and exfiltrate data from a compromised network. It involves encapsulating data within DNS queries and responses, which are then transmitted through the Domain Name System (DNS). 

DNS is a critical component of the internet that translates human-readable domain names (such as http://www.google.com) into machine-readable IP addresses (such as 172.217.0.46). DNS queries and responses are typically allowed through firewalls and other security measures because they are necessary for accessing web pages and other online services. However, DNS Tunneling takes advantage of this inherent trust in DNS and uses it as a covert channel for transmitting data. 

To use DNS Tunneling, cybercriminals first establish a command and control (C2) channel with a compromised host on a network. This C2 channel is used to send and receive data through DNS queries and responses. The data is encoded within the DNS queries and responses in a way that is not easily detectable. 

There are several techniques used in DNS Tunneling, including: 

• Subdomain DNS Tunneling: In this technique, cybercriminals create subdomains that contain encoded data. The cybercriminal sends DNS queries to the compromised DNS server to retrieve the data encoded in the subdomains. 
• TXT Record DNS Tunneling: TXT records are typically used to provide additional information about a domain, but can be used to transmit data in a DNS Tunneling attack. The cybercriminal encodes the data within the TXT record and sends a DNS query to the compromised DNS server to retrieve the data. 
• DNS Flag DNS Tunneling: DNS flags are used to indicate the status of a DNS query or response. By manipulating these flags, cybercriminals can send and receive data through DNS queries and responses. 

DNS Tunneling is a powerful technique for bypassing network security controls because it exploits the ubiquitous nature of DNS and the fact that DNS queries and responses are typically allowed through firewalls and other security measures. This makes it difficult to detect and prevent DNS Tunneling attacks. 

The Risks of DNS Tunneling 

DNS Tunneling poses a significant risk to organizations and individuals alike. Here are some of the risks associated with DNS Tunneling: 

1. Data Exfiltration: DNS Tunneling is a powerful technique for exfiltrating data from a compromised network. Cybercriminals can use DNS Tunneling to exfiltrate sensitive data such as passwords, credit card numbers, and other confidential information. Because DNS queries and responses are typically allowed through firewalls and other security measures, DNS Tunneling can be difficult to detect and prevent. 
2. Command and Control: DNS Tunneling is also a powerful technique for establishing command and control channels with compromised hosts. Cybercriminals can use DNS Tunneling to send and receive commands to compromised hosts, allowing them to control the compromised hosts remotely. 
3. Malware Distribution: DNS Tunneling can also be used to distribute malware to compromised hosts. Cybercriminals can use DNS Tunneling to send malware payloads to compromised hosts, which are then executed on the compromised hosts. 
4. Botnet Operation: DNS Tunneling is a common technique used in the operation of botnets. Botnets are networks of compromised hosts that are controlled remotely by cybercriminals. DNS Tunneling is used to establish command and control channels with the compromised hosts and to exfiltrate data from the compromised hosts. 
5. Reputation Damage: DNS Tunneling can damage an organization’s reputation if its network is compromised and used for malicious purposes. Cybercriminals can use DNS Tunneling to exfiltrate sensitive data from an organization’s network, which can result in significant financial losses and reputational damage.
6. Network Slowdowns: DNS Tunneling can also cause network slowdowns and disruptions. Because DNS queries and responses are typically allowed through firewalls and other security measures, cybercriminals can use DNS Tunneling to bypass security measures and flood a network with DNS queries. This can cause significant network slowdowns and disruptions, making it difficult for legitimate users to access network resources. 
7. Compliance Violations: DNS Tunneling can also result in compliance violations. Many industries, such as healthcare and finance, have strict regulations regarding the handling of sensitive data. If an organization’s network is compromised through DNS Tunneling, it may be in violation of these regulations and could face significant financial penalties. 
8. Data Loss: DNS Tunneling can also result in data loss. Cybercriminals can use DNS Tunneling to exfiltrate sensitive data from an organization’s network, which can result in significant financial losses and reputational damage. Additionally, if an organization’s network is flooded with DNS queries as part of a DNS Tunneling attack, legitimate network traffic may be lost or delayed, resulting in data loss. 
9. System Crashes: DNS Tunneling can also cause system crashes. If a network is flooded with DNS queries as part of a DNS Tunneling attack, it can overload the network and cause systems to crash. This can result in significant downtime and financial losses for an organization. 
10. Legal Liability: Finally, DNS Tunneling can also result in legal liability for an organization. If an organization’s network is compromised through DNS Tunneling, it may be held legally liable for any damages resulting from the attack. This can include financial damages, reputational damage, and legal fees associated with defending against lawsuits.

Read More 15 Types of Cyber Attacks You Need to Know

Real Examples of DNS Tunneling

FIN7

In 2017, the cybercriminal group FIN7 used DNS tunneling to exfiltrate stolen data from compromised systems. FIN7 is known for its sophisticated attacks on the hospitality and retail industries, and has been linked to the theft of millions of payment card records. In this attack, FIN7 used a tool called “DNSMessenger” to communicate with its command and control server through DNS queries and responses. By using DNS tunneling, FIN7 was able to bypass security tools that were only monitoring traditional network traffic, as DNS traffic is often allowed to pass through firewalls and other security measures. This allowed FIN7 to exfiltrate stolen data from compromised systems without being detected for months. 

DNSMessenger 

In 2016, researchers discovered a new malware called DNSMessenger that used DNS tunneling to communicate with its command and control server. The malware was spread through phishing emails and targeted primarily the defense sector. Once installed on a system, DNSMessenger would use DNS queries and responses to send and receive commands and exfiltrate stolen data. The use of DNS tunneling allowed the malware to bypass traditional network security controls, as DNS traffic is often allowed to pass through firewalls and other security measures. The malware was designed to be stealthy, making it difficult to detect and block. 

PinkStats

In 2017, a new strain of malware called PinkStats was discovered that used DNS tunneling to exfiltrate data from compromised systems. PinkStats was spread through malicious email attachments and targeted primarily the financial sector. Once installed on a system, PinkStats would use DNS queries and responses to send stolen data to its command and control server. This technique allowed the malware to evade detection by security tools that were not monitoring DNS traffic. The use of DNS tunneling made it difficult for defenders to block the malware and prevent data exfiltration. 

Operation Potao Express

In 2014, researchers uncovered a cyber espionage campaign called Operation Potao Express, which used DNS tunneling to exfiltrate data from targeted organizations. The attackers used custom-built malware to infect systems and then used DNS queries and responses to communicate with their command and control server. 

The use of DNS tunneling allowed the attackers to bypass traditional network security controls and evade detection. The attackers were able to exfiltrate sensitive data from targeted organizations, including government agencies and military organizations, for several years before being discovered.

DNSpionage

In 2019, a new threat actor group called DNSpionage was discovered using DNS tunneling to exfiltrate data from targeted organizations. The group primarily targeted organizations in the Middle East, particularly those in the government and energy sectors. The group used spear-phishing emails to deliver malware to targeted systems, and then used DNS tunneling to communicate with their command and control server and exfiltrate data. 

DNSpionage used a custom-built malware called “Karkoff” to carry out its attacks, which was designed to be stealthy and avoid detection by traditional security measures. The use of DNS tunneling allowed DNSpionage to bypass network security controls and evade detection, making it a particularly effective technique for the group.

Conclusion

DNS Tunneling poses a significant danger to network security and privacy. As a technique that can be used to bypass network restrictions, exfiltrate data, and establish command and control channels with compromised hosts, DNS Tunneling attacks can be difficult to detect and prevent. Furthermore, attackers can use DNS Tunneling to steal sensitive information and compromise the integrity of network traffic, potentially leading to devastating consequences for organizations and individuals alike. To mitigate the risks associated with DNS Tunneling, organizations must take proactive measures to protect their networks.