How Multi-Level Domains Can Hide Cyber Attacks

The domain name system (DNS) is the backbone of internet navigation, translating domain names into IP addresses that enable users to access websites and online services. While DNS plays an essential role in the functioning of the internet, it also offers opportunities for cybercriminals to exploit its structure for malicious purposes. One such method involves the use of multi-level domains, which can serve as a sophisticated means of hiding cyberattacks and evading detection. By leveraging multiple levels of subdomains, attackers can obfuscate their activities, bypass security filters, and carry out a variety of nefarious operations without being easily traced. Understanding how multi-level domains are used in cyberattacks is essential for organizations and security professionals aiming to defend their networks and systems from these evolving threats.

A multi-level domain refers to a domain that includes several layers of subdomains, often appearing as a long string of seemingly random or meaningless characters before the top-level domain (TLD). For example, instead of a simple domain like “example.com,” a multi-level domain might take the form of “a.b.c.d.e.f.example.com.” Each subdomain, separated by periods, creates an additional layer within the domain hierarchy. While subdomains are commonly used in legitimate ways to organize content and services under a single domain, such as separating “mail.example.com” from “shop.example.com,” attackers have learned to exploit the flexibility of this structure to hide their malicious operations.

One of the primary ways that multi-level domains are used in cyberattacks is by generating dynamically changing subdomains to evade detection. Many traditional security tools, such as firewalls, intrusion detection systems (IDS), and web filters, rely on domain blacklists or reputation-based systems to block known malicious domains. However, by using multi-level domains with constantly changing subdomains, attackers can bypass these defenses. For instance, a command-and-control (C2) server controlled by an attacker might generate new subdomains every few minutes or hours, making it difficult for security tools to keep up with the changes. Even if one subdomain is flagged and blocked, the attacker can quickly generate a new one, keeping the malicious operation running without interruption.

This technique, often referred to as “domain generation algorithms” (DGA), allows attackers to maintain communication with compromised systems while evading detection. DGAs are commonly used in botnet operations, where malware-infected devices (bots) regularly check in with a central C2 server to receive instructions. By using multi-level domains with randomized or algorithmically generated subdomains, attackers ensure that their communication channels remain open, even if some of their domains are blacklisted. The sheer number of possible subdomains that can be generated makes it nearly impossible for traditional security tools to block them all in real-time, giving attackers a significant advantage.

Multi-level domains can also be used to carry out phishing attacks by creating domains that closely resemble legitimate websites. Phishing is a common tactic used by attackers to steal sensitive information, such as login credentials or payment details, by tricking users into believing they are interacting with a legitimate service. By using subdomains, attackers can create URLs that appear to belong to a trusted domain, when in reality, the primary domain is controlled by the attacker. For example, a phishing URL might look like “login.bankname.com.security-check.example.com,” where “bankname.com” appears to be part of the URL, but the true domain is “example.com.” This method takes advantage of users’ tendency to focus on familiar terms in a URL while ignoring the full structure, making them more likely to fall for the phishing attempt.

Moreover, multi-level domains can be used to host malicious payloads or deliver malware without raising suspicion. Attackers often use cloud services, content delivery networks (CDNs), or other infrastructure providers that allow the creation of multiple subdomains under a single parent domain. By hosting malicious content on different subdomains, attackers can compartmentalize their operations and reduce the likelihood that security systems will detect the malicious activity. For example, a malware dropper may be hosted on “dropper.maliciousdomain.com,” while a separate subdomain, such as “payload.maliciousdomain.com,” serves the actual malware. Each part of the attack can be distributed across multiple subdomains, making it harder for security analysts to trace the entire attack sequence or detect the connections between the various components.

Additionally, attackers can exploit the multi-level domain structure to create complex URL redirection schemes. In a typical redirection attack, a user clicks on a link that appears legitimate but is redirected through multiple subdomains before landing on a malicious website. Each step in the redirection chain can pass through different subdomains, often hosted on different servers, further complicating detection and analysis. These redirections can be used to evade URL filtering systems that block direct access to known malicious sites. The multiple layers of subdomains obscure the final destination, making it more difficult for users and automated systems to recognize the threat until it’s too late.

In some cases, multi-level domains are used in combination with encrypted traffic, such as DNS over HTTPS (DoH) or DNS over TLS (DoT), to further hide malicious activities. Encrypted DNS traffic prevents security tools from inspecting DNS queries and responses, making it harder to detect and block malicious domains. When attackers combine encrypted DNS with multi-level domains, they can create a stealthy attack pipeline that bypasses traditional security measures. This not only allows attackers to hide the true nature of their operations but also makes it more difficult for security teams to identify the compromised systems and trace the attack back to its source.

One particularly concerning aspect of multi-level domain usage in cyberattacks is its ability to circumvent some of the most advanced security solutions. Many modern security platforms use machine learning and behavioral analysis to detect anomalies in domain usage, but the constantly shifting nature of multi-level domains can generate enough noise to confuse these systems. Attackers may generate hundreds or thousands of subdomains, with only a small fraction used for malicious purposes, making it difficult to distinguish legitimate traffic from malicious activity. This flood of domain-related traffic can overwhelm security tools, allowing the attacker to slip through the cracks.

To make matters worse, attackers can combine multi-level domains with other techniques, such as domain shadowing or subdomain takeovers, to further obscure their activities. Domain shadowing involves the use of compromised domain accounts to create subdomains that appear legitimate but are controlled by the attacker. Subdomain takeovers occur when an attacker gains control of a subdomain that was previously linked to an abandoned or misconfigured external service. Both techniques rely on the multi-level domain structure to carry out attacks in a way that remains hidden from security tools and unsuspecting users.

For defenders, the challenge of detecting and mitigating multi-level domain attacks requires a combination of advanced threat intelligence, real-time monitoring, and proactive security measures. Traditional domain blacklists are no longer sufficient to combat the dynamic nature of these attacks. Instead, organizations must adopt security solutions that can analyze domain reputation, detect patterns of domain generation, and identify unusual domain structures that may indicate malicious activity. Additionally, implementing strict access controls, including domain locking and secure DNS configurations, can help reduce the risk of domain abuse.

In conclusion, the use of multi-level domains by cybercriminals presents a significant challenge to modern security defenses. By exploiting the flexibility of the DNS system and leveraging subdomains in creative ways, attackers can hide their operations, evade detection, and carry out a wide range of attacks, from phishing and malware distribution to botnet communication and internal network compromise. As cyber threats continue to evolve, it is critical for organizations to stay vigilant, adopt advanced security tools, and understand the complexities of how multi-level domains can be used to hide and perpetuate cyberattacks. Only by addressing this growing threat can organizations effectively protect their assets and maintain the security of their digital environments.

The domain name system (DNS) is the backbone of internet navigation, translating domain names into IP addresses that enable users to access websites and online services. While DNS plays an essential role in the functioning of the internet, it also offers opportunities for cybercriminals to exploit its structure for malicious purposes. One such method involves…