What is DoS Attack?

DoS in cybersecurity stands for Denial-of-Service. DoS attacks aim to make a system or network unavailable to its intended users by overwhelming it with malicious traffic or exploiting system vulnerabilities.  

Whether it's a small business or a multinational corporation, no entity is immune to these disruptions, which can lead to severe financial and reputational damage.

In this article, we will learn the definition of Denial of Service attacks, understand different types of DoS attacks, and look at significant DoS attacks in history. We have also explained how DoS attacks are carried out and how to prevent them.

Furthermore, you can also join our cyber security training to learn more about the technical details of Denial-of-service attacks and how to resolve them.

What is DoS Attack? 

A Denial-of-Service (DoS) attack is a cyberattack that attempts to overload a website, server, or network with excessive traffic or requests, causing significant slowdowns or complete unavailability of services. 

Typically, a DoS attack uses a single machine to flood the target, exhausting its resources and preventing it from handling legitimate requests. Successful attacks can lead to partial or total service outages and often require substantial time and resources to detect, mitigate, and recover from. 

The MITRE ATT&CK framework categorizes denial-of-service attacks under several techniques, primarily including T1499: Endpoint Denial of Service, T1498: Network Denial of Service, and T1499.001: OS Exhaustion Flood.

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How is Denial-of-Service Attack Carried Out? 

A Denial-of-Service (DoS) attack is carried out by flooding a server, network, or service with excessive traffic, making it inaccessible to legitimate users. Attackers use a single system to send multiple requests to the target system so that it uses most of its resources to handle those requests.

DoS attacks can exploit bandwidth, system resources, or application vulnerabilities. Common methods include SYN floods, UDP floods, and HTTP request floods. The goal is to exhaust resources, causing slowdowns or complete service outages. DoS attacks can lead to financial loss, reputational damage, and service disruption.

For example, a SYN flood sends repeated TCP connection requests without completing the handshake, leaving the server waiting indefinitely. Over time, the server becomes overwhelmed with half-open connections, blocking legitimate traffic. Other attacks may use malformed packets or exploit memory leaks to trigger system crashes. 

Types of DoS Attacks

There are six types of DOS attacks: 

1. Teardrop Attack 

In a teardrop attack, fragmented packets are sent to the target system with overlapping or malformed offsets. When the system tries to reassemble them, it crashes or becomes unstable due to the improper handling of the corrupted packet structure. This was more effective against older operating systems. 

2. Flooding Attack 

A flooding attack overwhelms a system or network with an enormous volume of traffic or requests, exhausting resources like bandwidth, memory, or CPU. Common examples include ICMP floods and SYN floods, which can quickly bring services to a halt. 

3. IP Fragmentation Attack 

This technique involves sending fragmented IP packets in a way that consumes the target's resources during reassembly. These fragments are either incomplete or designed to never fully assemble, causing systems to allocate memory unnecessarily until they crash. 

4. Volumetric Attack 

Volumetric attacks generate massive amounts of data to saturate the target’s internet bandwidth. This prevents legitimate users from accessing the system. Examples include DNS amplification and UDP floods, often carried out using botnets. 

5. Protocol Attack 

 Protocol attacks exploit weaknesses in Layer 3 and Layer 4 protocols, such as TCP, ICMP, or DNS. They consume connection state tables on servers, firewalls, or load balancers by initiating partial connections or malformed packets, leading to system resource exhaustion. 

6. Application-Based Attack 

These attacks target specific applications or services at Layer 7 of the OSI model. By mimicking legitimate requests, they are harder to detect and can bring down web servers or APIs using relatively low traffic volumes. HTTP floods are a common form of this attack. 

Top 3 Real-World DoS Attacks in History 

Here are some well-known DoS attack examples: 

1. Panix SYN Flood Attack (1996) 

In September 1996, New York-based ISP Panix became one of the first known victims of a SYN flood DoS attack. The attacker overwhelmed Panix's servers with a high rate of SYN packets—between 150 and 210 per second—causing significant service disruptions over several weeks.  

2. Royal Family Website Attack (2023) 

On October 1, 2023, a denial-of-service attack caused royal.uk, the official website of the British royal family, to be down for almost ninety minutes. Although their involvement was not verified, the pro-Russian hacker collective KillNet took credit. During the incident, no private information was compromised. 

3. Pennsylvania Courts DoS Attack (2023) 

In September 2023, Pennsylvania's state court system experienced a DoS attack that disrupted several online services, including docket sheets and electronic case filings. Despite the disruption, court operations continued with paper filings, and no data breaches occurred.  

How DoS Attack Impacts an Organization

Denial of Service attacks are very harmful because they impact the services of web applications. Below, we have explained how a DoS attack impacts an organization:

1. It interrupts access to websites, applications, or online services.

2. Causes revenue loss due to downtime and recovery costs.

3. Damages customer trust and brand reputation.

4. Can expose vulnerabilities, leading to further attacks.

5. Consumes bandwidth and server resources, affecting performance.

How to Identify DoS Attacks?

If you want to identify whether your system is compromised by a DoS attack or not, you should watch for signs like unusually slow network performance, frequent website timeouts, or complete service unavailability.

You can also check for spikes in traffic from a single IP or multiple sources, which may indicate a Distributed DoS (DDoS) attack. Check your server logs for repeated requests to the same resource or protocol anomalies.

Start using network monitoring tools to detect abnormal traffic patterns. If legitimate users report access issues while your system resources are maxed out, it's likely under a DoS attack. Early detection is key to minimizing damage and restoring service.

DoS Attack Indicators

1. Sudden Traffic Spikes: Unusual surges in incoming traffic, especially from unknown or suspicious sources.

2. Service Unavailability: Websites or applications become slow, unresponsive, or completely inaccessible.

3. Repeated Requests: High volume of identical or malformed requests targeting specific endpoints or services.

4. Resource Exhaustion: Server CPU, memory, or bandwidth usage maxes out unexpectedly.

5. Alerts from Monitoring Tools: Security or network monitoring systems flag anomalies or potential threats in real-time.

How to Protect Yourself from DoS Attacks 

While it’s impossible to prevent all attacks, several strategies can significantly reduce the risk and impact of DoS attacks:

1. Use DoS Protection Services

You can use security services like Cloudflare or AWS Shield to absorb and filter malicious traffic before it reaches your server. These platforms offer real-time threat detection, traffic analysis, and mitigation to keep services online during attacks.

2. Apply Rate Limiting

Rate limiting restricts the number of requests a user can make in a given time frame. You can implement rate limiting in your application as it will help prevent abuse and reduce the risk of request floods overwhelming your application or server.

3. Keep Systems Updated

Regularly updating your operating systems, applications, and security patches minimizes vulnerabilities that attackers could exploit in DoS attacks, ensuring your infrastructure is resilient against known threats and exploits.

4. Monitor Network Traffic

Use network monitoring tools to track traffic patterns and detect anomalies early. Unusual spikes or irregular behavior can indicate an ongoing or impending attack, allowing for quicker response and mitigation.

5. Develop a Response Plan

Develop and maintain an incident response plan that outlines roles, communication protocols, and recovery steps. A prepared team can act swiftly to minimize downtime and damage during a DoS or DDoS attack.

DoS vs DDoS Attack

Here's a concise table explaining the difference between DoS and DDoS attacks: 

Conclusion 

Denial-of-Service attacks represent a persistent threat in the cybersecurity landscape, capable of halting critical services and causing extensive damage. Whether through proper configuration, intelligent traffic handling, or proactive monitoring, organizations and individuals can strengthen their defenses and minimize the impact of these DoS attacks.