A SYN flood attack is a form of Denial of Service (DoS) attack in which the attacker attempts to disable a server or network by overloading it with SYN packets. This attack uses a feature of the TCP handshake, the method by which network devices establish a connection for communication.
To understand how a SYN flood attack works, it is important to know the normal TCP handshake process, which has three steps:
In a SYN flood attack, however, the attacker sends SYN packets to the target server at high speed and in large numbers without ever completing the connection with an ACK packet. After receiving each SYN packet, the server waits for the corresponding ACK to complete the handshake. In the meantime, the server reserves resources and holds these “half-open” connections in a queue.
As no final ACK packets are received, more and more half-open connections accumulate until the server’s resources are exhausted. Eventually, the server is no longer able to process legitimate requests because it is overloaded with the false SYN requests. As a result, legitimate users no longer have access to the server, which is the purpose of the DoS attack.
A SYN Flood (DDoS) attack exploits a weakness in the three-way handshake of the TCP protocol to make a server or service inaccessible. An attack typically proceeds as follows:
A SYN flood attack can be effective because it exploits the asymmetry of resource consumption between a client and a server – the attacker only has to send small SYN packets, whereas the server has to use comparatively more resources to respond to each request and maintain the connection.
There are three basic types of SYN flood attack. In a direct attack, a single attacker sends a flood of SYN packets to the target server. This can be carried out using a powerful computer or a server with a high bandwidth connection. Since the requests in this type of attack come from a single source, the attack is relatively easy to detect and block.
In a distributed SYN flood attack, several computers (botnet) send SYN packets to the target server at the same time. These attacks are more difficult to detect and combat. They require more advanced techniques such as IP verification and anomaly detection.
The third possibility is a spoofed SYN flood attack. This involves spoofing the IP addresses of SYN packets so that they appear to come from different sources. This makes it difficult to trace the source of the attack and differentiate between legitimate and spoofed traffic.
Defending against SYN Flood (DDoS) attacks can be challenging, but there are several techniques and strategies that can be used to minimize or prevent the impact of this type of attack. Below are some methods to defend against SYN Flood attacks:
It is often worth combining multiple approaches to ensure the best possible defense against SYN flood attacks. It is also crucial that networks and servers are constantly monitored and updated to ensure that they are armed against the newer and more covert versions, as hackers are always updating their methods.
A professional DDoS protection solution is the usual way to effectively protect against such attacks. AI-based systems in particular are able to quickly detect and mitigate those attacks before any damage is done to your site.
If you have any questions about such a specialized solution, our cyber experts will be happy to assist you at any time and advise you on a tailor-made implementation without obligation.