Denial of Service / DoS
DoS is a denial-of-service attack that tries to bring a service down or slow it so far that legitimate users can no longer use it. Unlike DDoS it need not come from a large network of compromised devices. Sometimes one source and a well-chosen vulnerability are enough.
Term
description · examples · notesDoS is a denial-of-service attack that tries to bring a service down or slow it so far that legitimate users can no longer use it. Unlike DDoS it need not come from a large network of compromised devices. Sometimes one source and a well-chosen vulnerability are enough.
Description
DoS can bury a service in requests, but it can also exploit a specific flaw in the application, the protocol or the configuration. A small number of specially shaped requests can consume a great deal of memory, hold connections open, crash a parser, or push the application into doing whatever costs it the most.
DoS is therefore not always a question of traffic volume. Sometimes it is a question of leverage: the attacker sends little and the server spends a lot. If the application has no limits, timeouts, rate limiting and sane error handling, one narrow part of the system becomes the reason the service is blocked.
Examples
- A specially prepared request crashes the service through a flaw in the parser.
- The attacker opens a large number of connections and keeps them active without sending any useful traffic.
- One endpoint triggers a heavy database operation, so a small number of requests consumes all the processing capacity.
Notes
- DoS is not automatically less serious than DDoS merely because it comes from fewer sources. If it hits the right vulnerability, the result is the same.
- The defense begins in the design: limits, timeouts, control of expensive operations, and how the application behaves under load.
Mentioned in the news
- 18. JUN 2026. NGINX zakrpe traže brzu proveru: nije svaki server pogođen, ali oni koji jesu predstavljaju visok rizik →
- 18. MAJ 2026. NGINX ranjivost CVE-2026-42945 već se koristi u napadima →
- 7. MAJ 2026. Cisco DoS ranjivost može oboriti CNC i NSO sisteme do ručnog restarta →
- 29. MAR 2026. Tri ranjivosti u BIND 9 mogu oboriti DNS servere i zaobići kontrole pristupa →
- 11. MAR 2026. Zero-day ranjivost u Microsoft .NET omogućava rušenje aplikacija →
- 7. MAJ 2026. Apache zakrpio HTTP/2 ranjivost koja može dovesti do DoS-a i potencijalnog RCE-a →
Techniques
carried out with 2Techniques used to carry it out. Select one to open its page.
Defenses
countered by 4How it is defended against. Select one to open its page.