Denial-of-Service (DoS) Attack

A denial-of-service attack overwhelms a single target — a server, application, link, or device — from one or a few sources, with the goal of degrading or stopping its service. Techniques range from volumetric floods (saturating bandwidth) and protocol abuse (e.g., SYN floods exhausting connection state) to resource exhaustion at the application layer (slow HTTP attacks, expensive queries) and logic flaws that crash the service. While DoS attacks come from a single origin or a small set of hosts (distinguishing them from DDoS), they can still be very effective against under-provisioned systems. Defences include rate limiting, capacity planning, anycast, upstream filtering, and code hardening against resource-amplifying inputs.