What is a DDoS Attack?

A Distributed Denial of Service (DDoS) attack is a malicious attempt to disrupt the normal traffic of a targeted server, service, or network by overwhelming it with a flood of internet traffic from multiple sources. This is typically achieved using a network of compromised computers called a botnet to generate an extremely high traffic volume, rendering the target unavailable to legitimate users.

Unlike single-source DoS attacks, DDoS attacks leverage thousands or even millions of hijacked devices, making them particularly difficult to mitigate. These attacks can target various layers of the network stack, including network infrastructure, transport protocols, and application services. Modern DDoS attacks often combine multiple techniques simultaneously and can reach terabits per second in volume.

The impact of successful DDoS attacks extends beyond immediate service disruption, potentially causing significant financial losses through downtime, customer dissatisfaction, reputation damage, and recovery costs. Organizations increasingly implement multi-layered defense strategies combining traffic filtering, rate limiting, traffic analysis, and cloud-based mitigation services to protect against these evolving threats.

How Does a DDoS Attack Work?

Imagine you have a store that operates smoothly with the normal flow of customers. Now, imagine if a large group of people, all at the same time, decided to flood your store, crowding the entrance and occupying all the space inside. Real customers can't get in to buy anything because the store is too crowded with people who aren't there to shop.

A DDoS attack is similar but happens online. Cybercriminals use thousands or millions of infected computers, called a botnet, to simultaneously send overwhelming internet traffic to a specific website or online service. This causes the website to become slow or completely unavailable, preventing real users from accessing it. The goal is to disrupt the site's regular operation, making it difficult or impossible for real visitors to access it.

Attackers exploit network device or software vulnerabilities to gain control and launch the attack. Because these attacks involve many devices worldwide, finding the source and reducing the damage is challenging.

What makes modern DDoS attacks particularly dangerous is their sophistication and adaptability. Today's attackers often employ multi-vector approaches, simultaneously targeting different vulnerabilities in a system's infrastructure. They might combine volumetric attacks (overwhelming bandwidth), protocol attacks (exhausting server resources), and application layer attacks (targeting specific web applications) to maximize disruption.

The attackers can also employ "low and slow" techniques that fly under the radar of traditional detection systems by mimicking legitimate traffic patterns while gradually degrading performance. Many attacks now feature built-in persistence mechanisms that automatically adjust tactics when they encounter resistance, making mitigation an ongoing battle rather than a one-time defense.

How to Recognize a DDoS Attack

Detecting the signs of a DDoS attack early is crucial for minimizing potential damages. It is vital to pay careful attention to the signs of a DDoS attack as they are often misread as benign, routine availability issues. Several of the leading indicators of a DDoS attack are:

• Sudden, unexplained slowdown or complete unavailability of your website or online services
• Unusual increase in spam emails received
• Detection of a significant increase in requests from a single IP address or a specific range of IP addresses
• Application errors or server crashes
• Unexpected spikes in traffic analytics without a corresponding increase in legitimate user engagement
• Slow upload or download performance speeds
• A website is temporarily unavailable
• Dropped internet connections
• Unusual or unexpected content

Types of DDoS Attacks

Several types of DDoS attacks target specific vulnerabilities. Understanding the different types of DDoS attacks helps optimize defenses and incident response tactics. The following are widely used types of DDoS attacks.

Visualization of a volumetric DDoS attack: from botnetunts of data traffic, preventing legitimate users from accessing the congested netw mobilization to service disruption as legitimate traffic is blocked by overwhelming packet floods.

Volume-Based or Volumetric Attacks

Volumetric attacks disrupt internet traffic by overwhelming a target's bandwidth or infrastructure capacity with massive amounts of data traffic, preventing legitimate users from accessing the congested network. Examples of such attacks include:

• UDP Flood: Sends many User Datagram Protocol (UDP) packets to random ports on a target server, forcing it to process false requests and exhaust its resources.
• ICMP Flood (Ping Flood): Uses the Internet Control Message Protocol (ICMP) to send a rapid succession of ping requests to the target, overloading the server with requests to respond to.
• DNS Amplification: Exploits open DNS servers to send an amplified amount of responses to the target by sending small queries that generate significant DNS responses to the target's IP address.
• NTP Amplification: Uses the Network Time Protocol (NTP) to send small requests that elicit significant responses from NTP servers to the target, amplifying the traffic volume significantly.
• HTTP Flood: Sends a large number of HTTP requests (including GET or POST requests) to a web server, consuming its resources or bandwidth.

Visualization of an application-layer DDoS attack with spoofed SYN packets.

Protocol Attacks

Protocol attacks exploit weaknesses in network protocol layers to disrupt the normal functioning of a targeted server, network, or service. By targeting these vulnerabilities, attackers can consume the resources of critical servers or network equipment, such as firewalls and load balancers, leading to service degradation or even complete unavailability. Examples of such attacks include:

• SYN Flood: Exploits the TCP handshake by sending multiple SYN requests without completing it, leaving the server with half-open connections and exhausting its resources.
• Ping of Death: Sends oversized or malformed packets to a target machine, causing it to crash or become unstable.
• Smurf Attack: Exploits ICMP by sending spoofed ping requests to a network's broadcast address, causing multiple devices to respond and overwhelm the target.
• Fragmentation Attack: Sends fragmented packets to the target, depleting resources during reassembly attempts.
• ACK Flood: Sends numerous ACK packets, part of the TCP/IP handshake process, to the target system, overwhelming it and causing service disruption.

Visualization of an application-layer DDoS attack: targeting server resources through seemingly legitimate requests that exhaust processing capacity.

Application Layer Attacks

Application layer attacks (Layer 7 Attacks) target the topmost layer of the OSI model, where web applications, APIs, and other application protocols operate. These attacks aim to disrupt data transmissions between hosts by targeting the web application packets. Application layer attacks are frequently combined with volumetric and protocol attacks, creating a multi-vector assault that can be challenging to mitigate effectively. Examples of such attacks include:

• HTTP Flood: Sends a high volume of HTTP GET or POST requests to overload the web server.
• Slowloris: Keeps numerous connections open by sending partial HTTP requests, preventing the server from processing new ones.
• DNS Query Flood: Overloads a DNS server with rapid, repeated queries.
• SQL Injection: Injects malicious SQL code into input fields to manipulate the database.
• Cross-Site Scripting (XSS): Embeds malicious scripts in web pages, targeting other application users.
• APIs Exploitation: Floods or exploits application programming interfaces (APIs) to disrupt service.

How to Prevent a DDoS Attack

DDoS attacks are notoriously challenging. Mitigating a DDoS attack involves proactive planning, real-time response, and implementing comprehensive security measures. Here are some key steps to help mitigate a DDoS attack:

Prepare in Advance

• Assess Risks: Understand your network infrastructure and identify potential vulnerabilities.
• Incident Response Plan: Develop and maintain a comprehensive DDoS response plan to ensure a swift and organized response.
• Training: Train your IT staff on recognizing and responding to DDoS attacks.

Implement Defensive Measures

• Use a Content Delivery Network (CDN): CDNs distribute traffic across multiple servers, helping absorb excessive traffic volumes.
• Deploy DDoS Protection Services: Use third-party DDoS mitigation solutions that provide robust filtering and traffic management.
• Web Application Firewalls (WAFs): Deploy WAFs to filter and block malicious traffic at the application layer.
• Network Firewalls and Intrusion Prevention Systems (IPS): Configure and maintain resilient firewall settings and IPS to detect and block malicious traffic.
• Rate Limiting: Set rate limits to control the requests a user can make in a specific timeframe.
• Traffic Analysis Tools: Use traffic analysis and monitoring tools to identify unusual patterns and detect attacks early.

On-Demand Mitigation

• Traffic Filtering: Filter and block malicious traffic based on IP addresses, traffic patterns, and anomalies.
• Blackholing or Sinkholing: Redirect unwanted traffic to a null route (blackholing) or a mitigation server (sinkhole) to protect the central server.
• Anycast Routing: Distribute traffic across multiple data centers using Anycast routing to absorb and mitigate the attack's impact.

Cloud-Based Mitigation

• Leverage Cloud Security Services: Use cloud-based DDoS protection services that can rapidly scale to absorb large traffic volumes.
• Auto-Scaling: Implement auto-scaling to handle excessive traffic by dynamically increasing capacity for web servers.

Post-Attack Analysis and Recovery

• Analyze Logs: Review network and application logs to understand the attack's nature and source.
• Patch Vulnerabilities: Identify and patch any vulnerabilities exploited during the attack.
• Update Security Protocols: Update and enhance your security measures based on lessons learned from the attack.
• Review Response: Conduct a post-incident review to assess the effectiveness of your response and improve your defense strategies.

Engage with Providers

• Internet Service Provider (ISP): Work closely with your ISP to identify and block malicious traffic upstream.
• DDoS Mitigation Services: Consider subscribing to specialized DDoS mitigation services that can provide additional layers of protection.

Notable Examples of DDoS Attacks

The following examples of DDoS attacks illustrate the impact of this cyberthreat, providing insights that help optimize security defenses by understanding the tactics and techniques used in previous attacks.

Dyn (2016)

The 2016 Dyn cyberattack was a significant DDoS incident that disrupted major services like Netflix and PayPal by targeting DNS provider Dyn. Using the Mirai botnet, it flooded Dyn's servers with 1.2 Tbps of malicious traffic. This high-profile incident revealed vulnerabilities in IoT devices and DNS infrastructure, increasing focus on securing these systems against similar DDoS threats.

Cloudflare (2020)

In 2020, Cloudflare faced one of its most significant DDoS attacks, peaking at 2.3 Tbps. The attack targeted a gaming customer and utilized over 600,000 devices.

Amazon Web Services (2020)

AWS was hit by a three-day DDoS attack that peaked at 2.3 Tbps. The attackers targeted an unidentified AWS customer and exploited misconfigurations in CLDAP servers to amplify the attack.

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