What is Syn Flood and how to protect yourself from the attack?

What is Syn Flood and how to protect yourself from the attack?

Digital security is an ever-present topic in the management of any company. The greater the amount of sensitive information accumulated by the business, the more important it is to invest in protection against different types of digital attacks. And one of the main ones is the Syn Flood attack.

Knowing and preventing these attacks is one of the main obligations of IT management in companies. Without due preparation, it can completely interrupt the company’s activities or cause the leakage of important data from customers, employees, and partners.

Follow and better understand what Syn Flood is and how to protect your business against it.

What is Syn Flood?

Syn Floods are a type of digital attack carried out to interrupt service within a network. This happens due to a flaw in a security check that the attacker tries to exploit.

When a user tries to connect to the company’s network, a procedure called Three Way Handshake must first occur. First, the user requests input with a SYN packet. Then, the server sends an acknowledgment response, a SYN-ACK. The user responds to this packet and the connection is established.

Syn Flood is when an attacker sends multiple connection requests from a fake IP. Thus, the server sends the SYN-ACK and waits for a response that never comes back, leaving the connection open. This can create a vulnerability within the system or, in sufficient quantities, take up all of the server’s bandwidth and impede its activities.

There are three main types of Syn Flood attacks, as we will see below.


The simplest format is when the attack starts from a single spoofed IP. However, it is one of the rarest types, as this tactic exposes the criminal. As there is only one connection path to the origin of the request, it is easier to track who carried out the attack.


Another path used in these attacks is to send several SYN packets from one IP address each. Thus, the criminal is not only able to overload the system but is also able to hide his tracks. It is also more difficult to distinguish which requests are legitimate and which are part of this attack.


DDoS attacks are more elaborate, often using a network of robots to carry out the attack. In many cases, the criminal installs malware on several computers and uses them to send the incoming requests to the server. It is an even more effective and dangerous method, as the only IP address that appears in the request is that of the machine containing the malware, not that of the criminal.

How to protect yourself against Syn Flood?

Given all these risks, it is important to take some actions to minimize the chances of this attack being successful. Here are some security actions you can take.

Adjust the number of connections

In addition to there being a limit on the number of active connections between the server and different users, there is also often an arbitrary limit on the number of requests that can be in the queue. When this limit is reached, the server stops accepting new requests and the service stops.

To avoid this, you can establish criteria to adjust this request limit, either automatically or manually. This way, the server can withstand an attack and maintain its functioning.

However, this is not the ideal solution, as a larger attack will eventually occupy the entire network capacity. It’s just a question of who has the most processing power.

Recycle old connections

Eventually, your network will reach the point where it can no longer extend the request queue and the criminal continues to send signals. In this case, the next step is to start “recycling” your connections, closing doors that have been open for the longest time to make room for new requests.

A common criterion here is waiting time. If a connection takes too long to establish, then the server closes the port. In this case, legitimate requests must be completed faster, or any space in the queue will be taken up again by fake IPs.

Use Cookies Syn

In this method, instead of cluttering the network with each request, the server deletes the request as soon as the SYN-ACK packet is sent, freeing up its memory. If you receive a response, the connection is reestablished and the process continues normally. Therefore, even in the event of an attack, there is no suspension of service.

The only problem with this method is that in some cases, a small loss of data occurs as part of the connection. However, it is still better than the alternative.

Use up-to-date protection software

As with any other type of attack, you can reduce the risks of Syn Flood by using digital protection software, especially the firewall. This way, you establish clearer criteria to identify an attempted attack and prevent it from affecting your systems.

Whenever one of these malicious connections is identified, the system can block the source IP temporarily, eliminating future attempts to establish a connection. In many cases, this is enough to mitigate its immediate impact.

What are the consequences or results of a Syn Flood attack?

There are two possible objectives for a Syn Flood attack: disrupting the server or creating a gateway. In the first case, the intention is to make the service inaccessible, which impacts work within the corporate environment and legitimate customer requests.

The second case is even more dangerous. If the connection is not eliminated correctly, the criminal can use it to enter the company’s system and gain access to your data. It can also serve as a distraction, occupying the IT team with these requests while other areas are accessed clandestinely.

To protect yourself against Syn Flood attacks, the most important thing is to understand how they work and what their objectives are. Only then can you define the best strategy to protect your network.

Do you want to know better to keep your business network well protected? Also, check out our article on how to protect yourself against ransomware.


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