What is a UDP Flood DDoS Attack?

Introduction

Burglars are opportunistic. They look for easy ways to get into your home: an unlocked door, an open first floor window, an unsecured garage, or a backdoor hidden from view where they can break in without anyone noticing. Cybercriminals are equally opportunistic. So, when it comes to DDoS attacks, UDP is an attack vector of choice because it is less secure. It provides an easy entry point to bring down your network which is why UDP flood DDoS attacks are so prevalent and potent.

In this blog, we’ll take an in-depth look at UDP flood DDoS attacks, including how they work, common techniques used, and their impact. We’ll compare them to other forms of DDoS attacks and also explain how you can protect against UDP flood DDoS attacks and prevent threat actors from using the technique to compromise network performance and service availability.

Understanding UDF flood DDoS Attacks

A UDP flood attack is a type of DDoS attack that targets the steps a server takes when it responds to a User Datagram Protocol (UDP) packet sent to one of its ports. Typically, when a server receives a UDP packet it will check to see if any programs that are running are listening for requests at that specified port. If not, the server responds that the destination is unreachable.

UDP is used to provide fast, efficient data transfer across networks, but it does not provide end-to-end reliability or flow control that is provided with other protocols. UDP is used when speed and efficiency are more important than reliability which is why we see it used in applications including online gaming, live streaming, and VoIP.

In a UDP flood DDoS attack, the attacker takes advantage of the connectionless and stateless nature of UDP, which makes it less secure, to overwhelm a target with traffic.

How UDP flood attacks work

UDP flood attacks are highly effective and require few resources to execute.

To initiate a UDP flood attack, attackers send a high volume of UDP packets to random ports on a targeted system. Because the system must check the port specified in each incoming packet for a listening application and issue a response, the targeted server’s resources can quickly become exhausted. Internet connections become congested and saturated preventing legitimate traffic from getting through. UDP flood attacks can also impact routers, firewalls, IPS/IDS, and WAF systems, overwhelming them with a large number of incoming UDP packets.

Exploiting UDP protocol characteristics

UDP is one of the most abused protocols for volumetric network DDoS attacks and with good reason. Some of the key characteristics that make UDP ideal for fast and efficient data transfer, also make it an ideal attack vector.

• Connectionless. UDP doesn’t establish a connection between the sender and the receiver as it sends data without confirming receipt or checking for errors. This makes data transmission faster but also less secure as there is no built-in way to verify the source or destination of the data.
• Stateless. UDP does not store data about interactions. It treats each packet independently without any knowledge of previous packets. This makes it hard to detect and mitigate UDP flood attacks as there is no way to track UDP packets and identify trends.

Common techniques used in UDP flood attacks

UDP flood attacks were once considered somewhat basic. But over the years they have become more complex, combining other techniques to maximize disruption.

• Amplification: The attacker takes advantage of vulnerable third-party servers including DNS and NTP servers, to amplify the volume of traffic being sent to the targeted server. The attacker uses a spoofed IP address to send a small request to these servers. In turn, these servers send a significantly larger amount of data to the target to amplify the impact by a factor of 50 or more.  
• Distributed reflective attacks: The attacker uses spoofed source IP addresses to overwhelm the spoofed IP address with response packets. This technique has the added benefit of ensuring the reply traffic does not reach the attacker while also disguising their behavior and anonymizing their location.
• UDP flood attack tools: Tools such as Low Orbit Ion Cannon (LOIC) and UDP Unicorn make it easy for hacktivist groups and other threat actors to launch UDP flood attacks.
• UDP Fragmentation: The attacker uses fragmentation to send large UDP packets (1500+) bytes to consumer more bandwidth with fewer packets. Since these fragmented packets are normally forged and have no ability to be reassembled, the victim’s CPU resources will be consumed by fruitless attempts to reassemble them. This technique can consume so much bandwidth that firewalls will indiscriminately drop good and bad traffic in order to stay up and running.

Impact of UDP flood DDoS attacks

UDP flood DDoS attacks degrade network performance, compromise service availability, and have significant financial implications.

Network performance: Excessive UDP traffic can saturate the network’s bandwidth and create network congestion. Overall performance of the network slows down and can become completely interrupted.

System and service availability: As servers attempt to respond to a massive volume of bogus UDP requests, their resources become drained and systems eventually crash, leading to service outages for legitimate users.

Financial impact: Ultimately, these types of compromises to business operations can have painful financial consequences. Beyond the costs of mitigation and recovery efforts from the attack, organizations may face significant losses in revenue, brand reputation, and customer trust.

Risk to critical business operations

The ripple effect of a UDP flood attack frustrates users of services like online gaming and can have a huge financial impact on gaming providers. However, these attacks also bring businesses that rely on digital communications to their knees – from the companies that deliver VoIP and live streaming services to those that rely on the use of these services to keep their businesses moving forward.

VoIP services have become an essential tool to conduct customer, partner, investor, and employee interactions. And live streaming services are essential for many organizations’ sales and marketing programs – user meetings, demonstrations, presentations, and training. Organizations across all sectors use these types of services and can be impacted by UDP flood DDoS attacks. But a particularly concerning example is in the healthcare sector where telehealth is increasingly popular. Anything that can potentially disrupt delivery of patient care presents significant risk.

These are just a few examples of the ripple effect of network performance degradation and service disruptions. Reliable communication and media services are integral to the success of business ecosystems. So, the importance of defending against UDP flood DDoS attacks has never been greater.

Comparing UDP flood attacks with other DDoS attacks

UDP flood attacks differ from other DDoS attacks in their use of the User Datagram Protocol, which is connectionless and does not require a handshake to establish a session. This makes UDP ideal for quickly sending a large volume of packets to saturate a target’s network without waiting for acknowledgments. The lack of a handshake also makes it difficult to detect and defend against UDP flood attacks. And the ability to use fragmentation can make the attack even more disruptive. Additionally, because UDP flood attacks are also relatively easy to execute, they are a popular tool among hacktivist groups that alternate between UDP and SYN floods in their attack waves.

These qualities set them apart from other DDoS attacks. For example:

• TCP-based methods involve more complex interactions and can be easier to trace due to the connection establishment process inherent in TCP.
• Application layer (layer 7) DDoS attacks are also more complex, targeting the application layer and seeking to exploit vulnerabilities in the software or applications running on the server.
• Protocol-based attacks like smurf attacks exploit vulnerabilities in the protocols used for communication between servers, consuming server resources and leading to service degradation.

Mitigating and defending against UDP flood DDoS attacks

UDP flood DDoS attacks will persist given the ease with which they can be deployed and their effectiveness. To defend against UDP flood attacks, organizations can use a combination of best practices and technology, including:

• Rate limit response traffic: Many operating systems limit the rate of the packets that are part of the UDP responses. This prevents systems from being overwhelmed by the flood of return packets. But this approach does not discriminate and may block legitimate traffic as well as illegitimate traffic.
• Rate limit incoming traffic: When possible, implement restrictions on the rate of incoming UDP traffic, but this could impact service reliability which can erode customer satisfaction.
• Minimize attack vectors: Use firewall-level filtering to block incoming UDP traffic on unused ports.
• Add firewall rules and IDS/IPS: Add firewall rules and implement IDS/IPS technology to detect and block activity that could indicate a UDP flood DDoS attack.
• Proactively monitor traffic: Know your baseline traffic patterns and continuously monitor for anomalous behavior that could indicate a UDP flood attack.
• Use a DDoS protection platform. The most comprehensive way to mitigate DDoS attacks, including UDP flood DDoS attacks, is with DDoS protection. The best solutions will allow you to maintain uninterrupted service availability even in the midst of a DDoS attack and protect you against follow-on threats including data leakage, ransom attacks, and other threats to your operations.

Conclusion

The use of UDP flood DDoS attacks to compromise network performance and service availability, and ultimately inflict financial pain on target organizations will continue. The connectionless and stateless characteristics of the UDP protocol that make it ideal for fast and efficient data transfer in applications like online gaming, VoIP, and live streaming, also make it an ideal attack vector.

Also concerning, UDP flood attack tools make it easier for hacktivist groups and other threat actors to launch UDP flood attacks. While techniques like amplification, fragmentation, and distributed reflective attacks have added to the complexity of UDP flood DDoS attacks, making them more damaging and more challenging to defend against.  

Fortunately, there are multiple best practices and technologies organizations can use to defend against UDP flood DDoS attacks, including rate limiting UDP traffic, minimizing attack vectors, adding firewall rules and IDS/IPS technology, proactively monitoring traffic and using a DDoS protection solution.

DDoS protection coupled with intelligence to stay ahead of emerging threats, provides uninterrupted service availability even in the midst of a UDP flood DDoS attack and can also protect you from other types of DDoS attacks and the follow-on malicious activity that can threaten your operations. Visit our threat intelligence research center for more information on DDoS defense in depth.