PowerDMARC

DNS Amplification Attacks: Examples, Detection & Mitigation

Milena Baghdasaryan
dns amplification attack

DNS Amplification attacks have increased by nearly 700% since 2016. The amplification factor in these attacks can range from 28 to 54 times the original query size. In extreme cases, it can reach up to 179 times amplification. 

In this article, we will explore what a DNS Amplification attack is, how it works, and how to detect and mitigate such attacks. We will also provide some real-world examples of DNS Amplification attacks that once shook the stability of DNS systems in recent times. 

Key Takeaways

What is a DNS Amplification Attack?

A DNS Amplification attack is a reflection-based Distributed Denial of Service (DDoS) attack where attackers exploit open and misconfigured DNS resolvers to flood a target with large volumes of DNS response traffic. 

In this attack, the cybercriminals make a DNS lookup request to a given open DNS server. They spoof the source address to make it the target’s address. When the DNS server returns the DNS record response, it gets sent directly to the victim’s IP address (the spoofed source address), not to a new target controlled by the cybercriminals.

This results in the victim receiving a flood of unrequested DNS responses, potentially overwhelming their network infrastructure and causing a denial of service.

This attack method is particularly dangerous because of its amplification factor, which, as mentioned above, can range from 28 to 54 times the original query size.

How DNS Amplification Attacks Work

The process of a DNS Amplification attack involves several steps:

Step 1: Spoofing the Victim’s IP

The attacker exploits a compromised device to transmit UDP packets with forged IP addresses to a DNS recursive resolver. The spoofed address matches with the real IP address of the victim.

Step 2: Sending Amplified DNS Queries 

Each UDP packet requests a DNS resolver, frequently using parameters like “ANY” to get the most extensive response possible.

Step 3: The Resolver Sends Large Responses

Upon getting the requests, the DNS resolver responds with extensive data and directs it to the spoofed IP address.

Step 4: Overwhelming the Target with Traffic

As the target’s IP address gets the response and the network infrastructure gets flooded with extensive traffic, it leads to a denial of service.

A small number of requests alone won’t compromise network infrastructure, but when this is multiplied and scaled up across several requests and numerous DNS resolvers, attackers can significantly amplify the volume of data directed at the target and overwhelm the victim’s network resources.

DNS Amplification Attack Examples

Over the past few years, there have been several DNS Amplification attacks that have shown the true potential and scale of the possible impact of such attacks:

Google Attack (2022)

On 1 June 2022, a DDoS attack targeted a Google Cloud Armour user with HTTPS for 69 minutes. At that time, this was the ‘largest’ distributed denial of service (DDoS) attack on record, with a peak of over 46 million requests per second. 5,256 source IPs from 132 countries were involved in the attack. According to Google, this was the largest Layer 7 DDoS attack and was nearly 76% bigger than the record before that.

Dyn Attack (2016)

On October 21, 2016, Twitter, Amazon, GitHub, and the New York Times were shut down because of the Dyn DDoS attack. The target of the attack was the company Dyn, which was responsible for serving a significant portion of the internet’s domain name system (DNS) infrastructure. 

The attack lasted for almost the whole day. The cybercriminals used “Mirai botnet” malware which utilized IoT devices (and not computers), as a result of which hackers could choose from over 50,000-100,000 devices (e.g. home routers, video recorders, etc.) to conduct the malware.

Spamhaus Attack (2013)

The Spamhaus DDoS attack began on March 18, 2013, and was one of the largest known DDoS attacks at the time, which peaked at around 300 Gbps. It was launched against Spamhaus, an anti-spam organization after they blacklisted CyberBunker, a hosting company known for its permissive policies. 

The attack exploited open DNS resolvers to amplify the traffic and used DNS reflection techniques that allowed the hackers to generate massive amounts of data with limited resources. The incident drew experts’ attention to the vulnerability of open DNS resolvers and their potential for abuse in large-scale DDoS attacks. Law enforcement agencies from several countries had to investigate the attack. This led to arrests, including that of a 17-year-old male from London.

How to Detect DNS Amplification Attacks

There are several methods you can use to detect DNS Amplification attacks.

Signs of a DNS Amplification Attack on Your Network

Some common signs of DNS Amplification attacks include: 

Tools and Methods for Detecting Suspicious DNS Traffic

SIEM systems aggregates and analyzes DNS logs for anomalies, such as unusual query volumes or destinations. Some popular recommendations include Splunk, IBM, and QRadar. 

These systems are quick to identify patterns of potentially suspicious DNS activities and trigger alerts based on these threats. Some tool recommendations include Snort and Zeek.

These tools provide real-time and historical analysis of DNS queries to detect anomalies. An example will be PowerDMARC’s DNS Timeline feature. 

EDR systems monitor endpoint DNS activity for signs of compromise, such as malware using DNS for command & control (C2). Examples include Microsoft Defender ATP and SentinelOne.

Proactive Measures to Prevent Suspicious DNS Activity

Metrics and Logs to Monitor (e.g., abnormal traffic patterns, query rates).

Analyzing DNS server logs for unusual patterns like abnormal traffic and repeated queries from the same source can help identify potential attacks at the initial stage. Here’s a summary of metrics to monitor: 

DNS Amplification Attack Mitigation

There are numerous effective mitigation strategies you can use.

Tools to Prevent DNS Amplification Attacks

1. Secure DNS Resolvers

Open resolvers are often exploited in DNS Amplification attacks and DDoS attacks, making it crucial to restrict access. So it’s best to disable open DNS Resolvers. You can instead, configure recursive DNS resolvers to only accept queries from trusted internal clients. Furthermore, it can be beneficial to restrict access to specific IPs or subnets using ACLs (Access Control Lists).

2. Implement Response Rate Limiting (RRL)

DNS Amplification attacks rely on sending numerous small requests to a resolver that generates large responses, overwhelming the victim’s network. To mitigate this, you can configure DNS servers to limit the rate of identical responses sent to a single IP. This can be achieved through implementing query-based rate limiting, reducing the impact of malicious repeated requests. A few examples of built-in RRL modules in popular DNS software are as follows:

3. Traffic Filtering 

Filtering DNS traffic can help block malicious queries, unauthorized access, and data exfiltration attempts. Additionally, Firewalls & Intrusion Prevention Systems (IPS) can help block suspicious DNS traffic.

Best Practices for Network Security

It’s important to practice proper network security to prevent DNS Amplification attacks. Here’s what you can do: 

Importance of Proactive Measures

Proactive actions like regular security audits, continuous monitoring, keeping up with industry news, and using the right tools can help you reduce the risk of successful attacks. Here’s why it’s important to take action fast: 

1. Prevent Large-Scale DDoS Attacks 

Taking proactive measures against DNS Amplification attacks can subsequently prevent large-scale DDoS attacks in the future. 

2. Reduce Network Overload 

DNS Amplification exploits can overload and overwhelm network systems, leading to outages and slowing down network operations. Taking swift action can prevent that from happening. 

Downtime as a result of DNS Amplification attacks can make companies lose a lot of money. It may even have legal implications for facilitating cybercrime. 

4. Uphold Organizational Reputation

If your DNS servers are under an Amplification exploit, it may lead to face loss and reputational damage. Prevention is imperative in such situations. 

Final Words

Becoming a victim of a DNS Amplification attack may be quite costly both from a financial and reputational perspective. It might make your domain and business come across as less trustworthy in the clients’ eyes and push them to look for alternative solutions. 

While they are quite hard to detect and prevent in the early stages, there are some common signs, methods, and tools to pay attention to that will help you identify and mitigate such attacks as early as possible.

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