What is a DoS Attack?
What is a DoS Attack?
A Denial of Service (DoS) attack is a type of cyberattack in which an attacker overwhelms a server or network with excessive traffic, rendering the service unavailable to legitimate users. While traditional DoS attacks focused on traffic overload, modern variants have evolved to exhaust critical system resources or exploit vulnerabilities in network protocols, effectively crippling entire services.
From a business standpoint, DoS attacks can lead to delayed website access, payment processing failures, and API disruptions. These incidents can significantly damage a company’s reputation. Therefore, DoS defense must be regarded not just as a technical necessity but as a crucial business continuity measure.
Evolution of DoS Attacks
DoS attacks have existed since the early days of the internet. As network and system architectures have become more complex, so too have the methods and scale of DoS attacks.
| Era | Key Characteristics |
| 1974 | First known DoS: A 13-year-old in Illinois simultaneously shut down 31 university terminals. |
| 1990s | Introduction of SYN flood attacks and ISP-targeted incidents. |
| 2000s | Rise of large-scale botnets marked the beginning of DDoS attacks. |
| 2010s | Application-layer attacks became widespread, affecting major companies like Amazon and Netflix. |
| 2020s | Attacks have evolved into sophisticated, multi-vector campaigns using IoT botnets. |
As the threat landscape has advanced, DoS attacks have grown from basic network traffic disruptions into complex, multi-layered assaults targeting web applications, APIs, and cloud infrastructure.
Main Types of DoS Attacks
DoS attacks can be classified based on the targeted layer and attack method: network-based, application-based, and distributed (DDoS).
Network and Protocol-Based Attacks
- Ping of Death: Sends oversized ICMP packets to overflow system buffers.
- Smurf/Fraggle Attack: Spoofs the victim’s IP to send ICMP or UDP packets to a broadcast address, flooding the target with amplified responses.
- SYN Flood: Overwhelms a server by sending numerous TCP connection requests without completing the handshake, exhausting connection queues.
- Teardrop Attack: Sends fragmented IP packets that overlap, causing system crashes.
These traditional attack types are generally mitigated by modern security solutions. Keeping systems up to date with security patches, using Access Control List (ACL) filters, and partnering with ISPs for traffic blocking policies are effective strategies.
Application (Layer 7) Attacks
- HTTP Flood: Overloads web servers and databases with a high volume of seemingly legitimate HTTP requests.
- Slowloris / Slow POST / R.U.D.Y. (R-U-Dead-Yet): Maintains long-lived HTTP connections with incomplete headers or payloads to exhaust server resources.
- DNS Flood: Floods DNS servers with rapid queries, depleting resources and preventing legitimate responses.
These attacks are best mitigated using Web Application Firewalls (WAF), which monitor and block malicious application-layer traffic.
Distributed Denial of Service (DDoS)
DDoS attacks utilize massive botnets—networks of infected devices—to launch traffic from multiple sources simultaneously. Each bot sends requests from a different IP, mimicking legitimate users and making detection difficult. This tactic overwhelms systems and networks, ultimately resulting in denial of service.
Because bots resemble normal traffic, identifying DDoS attacks requires reliable security services with advanced detection capabilities.
How to Defend Against DoS Attacks
The primary defense against DoS attacks is deploying a Web Application Firewall (WAF). A WAF inspects web traffic in real time and blocks threats such as SQL injection, cross-site scripting, and HTTP floods. Modern WAFs go beyond rule-based filtering and utilize AI-driven behavior analysis and machine learning to respond to sophisticated threats like multi-vector DoS attacks.
WAFs are especially effective against application-layer attacks such as Slowloris and R.U.D.Y., helping to maintain service availability.
An advanced alternative is Web Application and API Protection (WAAP). WAAP solutions offer integrated protection for web applications and APIs, as well as DDoS mitigation, bot detection, and data leakage prevention. For cloud and hybrid environments, WAAP enhances both visibility and unified policy management.
Penta Security’s DoS Defense Solutions:
✅ WAPPLES: An appliance-based WAF offering enterprise-grade protection.
✅ Cloudbric WAF+: A subscription-based WAF service optimized for cloud environments.
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Check out Penta Security’s product lines:
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Agent based Zero Trust Network Access Solution: Cloudbric PAS
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