Denial of Service: How Can It Cripple Systems?

Denial of Service: How Can It Cripple Systems?

 By Charles Joseph | Cybersecurity Advocate
 Last update: November 25, 2023

Denial of Service, often abbreviated as DoS, refers to a type of online attack where hackers overwhelm a network, service, or server with excessive requests. This overloads the system, causing it to slow down or crash. As a result, legitimate users are unable to access the service or network.

Denial of Service Examples

1. Buffer Overflow Attacks

A Buffer Overflow Attack is a common type of Denial of Service attack. The main idea behind this attack is to flood the network or server with more data than it can handle.

In this scenario, an attacker sends a deluge of data to a particular network address, completely overwhelming the system’s buffer capacity. The buffer is a temporary storage area for data, and when it’s filled beyond its limit, it can cause the system to crash or become unstable.

As a consequence of this overload, the system either slows down dramatically or stops working entirely. This prevents legitimate users from being able to access the services or data they need, which is the ultimate goal of a Denial of Service attack.

2. ICMP Flood

An ICMP Flood, also known as a Ping Flood, is another familiar type of Denial of Service attack. This attack’s aim is to disrupt the targeted service by sending an excessively large number of ICMP Echo Request packets, commonly known as “pings”.

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The attacker overwhelms the targeted server with these pings. In a normal interaction, a server would respond to each ping with an ICMP Echo Reply. However, in an ICMP Flood, the sheer number of pings forces the server to expend its resources trying to respond to each one.

This results in the server becoming heavily loaded and eventually unresponsive. Therefore, legitimate users trying to use the server find that they are unable to get the service or network access they require.

3. SYN Flood

A SYN Flood is another form of Denial of Service attack. In this case, the attacker’s goal is to exhaust the resources of a server by initiating and then intentionally failing to complete a connection process.

The attacker sends a synchonization (SYN) request to the target server to initiate a connection, but then does not respond to the server’s follow-up acknowledgement (ACK). This leaves the connection between the attacker and the server in an incomplete, or “half-open”, state.

By repeating this process, the attacker can create a significant number of these half-open connections. The server is forced to devote its resources to these bogus connections, leaving it less able to respond to legitimate requests. The end result is a denial of service to actual users.


Denial of Service attacks are a serious threat in the digital world, aiming to disrupt the availability of networks, services or resources. Understanding how these attacks work, such as Buffer Overflow Attacks, ICMP Floods, and SYN Floods helps in the development of more secure systems and the safeguarding of virtual spaces.

Key Takeaways

  • Denial of Service (DoS) attacks aim to make a network, service, or server unavailable to its intended users.
  • Buffer Overflow Attacks flood a network with more data than it can handle, causing it to crash or slow down.
  • ICMP Floods, or Ping Floods, disrupt services by sending a mass of ping requests, causing the server to overload in trying to respond.
  • SYN Floods overwhelm a server by initiating, but not completing, a large volume of connection requests, thus draining its resources.
  • Understanding these types of DoS attacks aids in the creation of safer, more secure digital environments.

Related Questions

1. How can individuals or organizations protect against DoS attacks?

There are several ways to protect against DoS attacks, including securing the network infrastructure with firewalls, routers, and other defense mechanisms, regularly updating and patching systems, and employing intrusion detection systems to find and mitigate threats early. It’s also vital to have a well-rehearsed incident response plan in case of an attack.

2. What’s the difference between a DoS and a DDoS attack?

A Denial of Service (DoS) attack comes from a single source, while Distributed Denial of Service (DDoS) attacks involve multiple connected devices, often forming a botnet, to flood the targeted network or server.

3. How exactly does an ICMP Flood overload a server?

An ICMP Flood overloads a server by sending a vast number of ping requests, known as ICMP Echo Request packets. The server tries to respond to each one, but the sheer volume of requests eventually overwhelms its resources.

4. Are there legal repercussions for perpetrating a DoS attack?

Yes. Legal penalties for conducting a DoS attack can be severe, including hefty fines or even jail time, depending on the damage caused. Laws vary from country to country, but DoS attacks are illegal in many jurisdictions.

5. What does the term ‘half-open connections’ mean in a SYN Flood?

‘Half-open connections’ in a SYN flood refers to connections that an attacker initiates but deliberately leaves incomplete. The server allocates resources for each of these incomplete connections, resulting in exhaustion of its resources and inability to handle legitimate requests.

"Amateurs hack systems, professionals hack people."
-- Bruce Schneier, a renown computer security professional