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Denial of Service Attack (DoS)

Security Glossary - Web Security

Definition: A Denial of Service (DoS) attack attempts to make a website or service unavailable by overwhelming it with traffic or exploiting vulnerabilities that cause crashes. A Distributed Denial of Service (DDoS) attack uses many compromised computers (a botnet) to generate attack traffic from multiple sources simultaneously.

Why DoS Is Important

DoS attacks directly impact availability, which is critical for any online business. Even brief periods of downtime during an attack can cause revenue loss, customer frustration, and reputational damage. For e-commerce sites, DDoS attacks during peak shopping periods are especially costly.

DDoS attacks come in three main categories: volumetric (flooding bandwidth with traffic), protocol (exploiting weaknesses in network protocols like SYN floods), and application layer (targeting specific application functionality with expensive requests like complex search queries).

Defending against DDoS requires infrastructure-level protection because the attack traffic can exceed your server's capacity. Cloud-based DDoS mitigation services (Cloudflare, AWS Shield, Akamai) absorb attack traffic at their edge network before it reaches your server. At the application level, rate limiting, request queuing, and efficient code reduce the impact of application-layer attacks.

Checking Your Setup

A security audit evaluates your site's resilience indicators including CDN usage, rate limiting, and server configuration. For DDoS protection, ensure you use a CDN or DDoS mitigation service. Test your rate limiting configuration and ensure your server has reasonable resource limits.

Run a Security Audit

Common Questions About DoS

How do I protect my site from DDoS attacks?
Use a CDN/DDoS mitigation service like Cloudflare (free tier available), AWS Shield, or Akamai. Implement rate limiting at the application level. Configure your server to handle connection limits gracefully. Have a DDoS response plan that includes contacting your provider.
Can a small site be a DDoS target?
Yes. DDoS-for-hire services make attacks accessible to anyone for a few dollars. Competitors, disgruntled users, or random attackers may target small sites. The cost of basic DDoS protection (like Cloudflare's free plan) is worth it for any site.

See Also

DNS Amplification Attack Rate Limiting Web Application Firewall Brute Force Attack Security Headers Overview
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