What is a DNS (Domain Name Server) Attack?
A DNS attack is the situation when an attacker either attempts to compromise a DNS network or uses its inherent attributes to conduct a broader attack. A well-orchestrated DNS attack can cause severe damage to an organization. DNS is the main form of communication. It receives domains entered by the user and maps them to an IP address. DNS attacks use this mechanism to perform malicious actions. For example, DNS tunneling techniques allow attackers to compromise network connectivity and gain remote access to the target server. Other DNS attacks can allow attackers to shut down servers, steal data, direct users to rogue sites, and perform DDoS attacks .
What is DNS?
To understand what a DNS attack is, let’s first remember it and how it works. DNS (Domain Name System) is a protocol that converts a domain name such as yoursite.com to an IP address such as 205.38.05.159. When users enter the domain name yoursite.com in a browser, the DNS resolver (a program in the operating system) searches for the numeric IP address or yoursite.com. Here’s how it works:
- The DNS resolver looks for an IP address in its local cache.
- If the DNS resolver can not find the address in the cache, it queries the DNS server.
- The recursive nature of DNS servers allows them to query each other to find the DNS server with the correct IP address or to find an authoritative DNS server that stores the canonical mapping of a domain name to its IP address.
- When the resolver finds the IP address, it returns it to the requesting program and also caches the address for future use.
Why Perform an Attack on the DNS?
DNS is a primary IP network and Internet service; therefore, it is required during most exchanges. Communication usually begins with DNS resolution. If the resolution service becomes unavailable, most applications will no longer work. Attackers often try to disallow the DNS service by bypassing the standard protocol function or using exploits and flaws. This can open the door to tunneling, data theft, and other exploits that exploit underground communications, as well as limiting the victim’s access to sites where they can find information on how to solve the problem.
Major Types of DNS attacks
Below are some of the methods used for DNS attacks:
📌 DNS Tunneling
DNS tunneling passes information through the DNS protocol, which typically resolves network addresses. Normal DNS queries contain only the information needed to communicate between the client and the server. DNS tunneling inserts an extra line of data into this path. It establishes communication that can bypass most filters, firewalls, and packet-capture software. This makes it difficult to detect and trace its origin. DNS tunneling can establish command and control or it can exfiltrate data. Information is often broken into smaller pieces, moved through the DNS, and collected at the other end.
📌 DNS Amplification
A DNS amplification attack is a DDoS attack in which attackers use available public DNS servers to flood the target with response DNS traffic. The attacker sends a DNS lookup request to a public DNS server with a fake source address, which is the target’s address. When the DNS server sends the response to the DNS record, it is sent to the target instead.
📌 DNS Flood Attack
DNS flooding attacks are another DNS-related type of DDoS attack that involves using the DNS protocol to perform User Datagram Protocol (UDP) flooding. Attackers deploy valid (not spoofed) DNS query packets at extremely high packet transmission rates and then create an array of raw IP addresses. Because the queries appear valid, the target DNS servers begin to respond to all queries. The DNS server can then be overwhelmed by a huge number of requests. In addition, the DNS attack requires a lot of network resources, which tires out the target DNS infrastructure until it is shut down. As a result, Internet access to the target is also reduced.
📌 DNS Spoofing
DNS spoofing or DNS cache poisoning uses security holes in the DNS protocol to redirect Internet traffic to malicious websites. They are sometimes referred to as man-in-the-middle attacks (MITM). This type of attack involves using altered DNS records to redirect online traffic to a rogue site that impersonates the intended recipient. When your browser goes online, it first queries a local DNS server to find the IP address for the website name. The local DNS server will request the address from the root servers that own the domain and then from the authoritative name server for that domain.
DNS poisoning occurs when an attacker interferes with this process and gives the wrong answer. Once he has tricked the browser into thinking he got the correct answer to his query, the attacker can redirect traffic to any fake website he wants. When the victim reaches the fake website, they are prompted to enter their login and password and log in to their account.
Once they enter data, they essentially give the attacker the ability to steal the credentials to access, and any sensitive information entered into the fraudulent login form. In addition, these malicious websites are often used to install viruses or worms on end-user computers, giving the threat actor long-term access to the machine and any data stored on it.
📌 NXDOMAIN Attack
The NXDOMAIN Flood DDoS DNS attack attempts to overload the DNS server by using a huge volume of requests for non-existent records. These attacks are often handled by the DNS proxy, which uses most (or all) of its resources to query the authoritative DNS server. This causes both the authoritative DNS server and the proxy DNS server to use all of their time to process invalid queries. As a result, response time to legitimate requests slows down until it eventually stops altogether.
📌 Botnet-based Attacks
A botnet is a series of devices connected to the Internet. It can be used to execute a distributed denial-of-service (DDoS) attack that steals data, sends spam, and allows an attacker to access the device and its connectivity. Moreover, botnets are a diverse and constantly evolving threat, so all of these attacks will inevitably evolve in parallel with our growing dependence on digital devices, the Internet, and new future technologies.
DNS Attack Prevention
The DNS service is like a giant contact list that a device uses to access a specified IP address. Implementing a solid security plan and following some basic security measures can help protect against evolving DNS attacks. Here are a few ways that can help you protect your organization from DNS attacks:
- Keep DNS Resolver Private and Protected. Limit the use of the DNS resolver to users on the network and never leave it open to external users. This will help prevent cache poisoning by external entities.
- Securely Manage Your DNS servers. Usually, authoritative servers can be hosted in-house, by a service provider, or by a domain registrar. You can get complete control if you have the necessary skills and experience for in-house hosting. If you don’t have the required skills, you can use the services of qualified professionals.
- Configure Your DNS Against Cache Poisoning. Configure security in your DNS software to protect your organization from cache poisoning. For example, try adding variability to outgoing requests to make it difficult for attackers to enter a fake response and get it accepted. Or try randomizing the request ID or using a random source port instead of UDP port 53.
As you can see, the DNS service is essential to the day-to-day operation of websites. The Internet is open to everyone, including cybercriminals who actively exploit weaknesses in a company’s security infrastructure. Therefore, a robust DNS security hardening policy will help organizations mitigate various DNS attacks.