Denial of Service (DOS) Attack

A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer resource unavailable to its intended users. During a Denial of Service (DoS) attack, a hacker renders a system unusable or significantly slows the system by over-loading resources or preventing legitimate users from accessing the system. This denial-of-service effect is achieved by sending messages to the target that interfere with its operation, and make it hang, crash, reboot, or do useless work.

The goal of DoS or DDoS isn’t to gain unauthorized access to machines or data, but to prevent legitimate users of a service from using it.
A DoS attack may do the following:

 Flood a network with traffic, thereby preventing legitimate network traffic.
 Disrupt connections between two machines, thereby preventing access to a service.
 Prevent a particular individual from accessing a service.
 Disrupt service to a specific system or person.

Both DoS and DDoS attacks are hard to handle. Defenses (firewalls, IDS, closed ports, patches updated) that work well against many other kinds of attacks are not necessarily effective against denial of service. The attack can consist of traffic that the firewall finds acceptable, probably because it bears a close resemblance to legitimate traffic. Since the DoS attack merely needs to exhaust resources, it can work on any port left open. Attackers can perform DoS attacks on machines that have no vulnerabilities, so patches to close vulnerabilities may not help.

Techniques : SYN Flood, Smurf, teardrop, land, ping of death
Tools : SSPing, Land Exploit, Smurf, Syn Flood, Jolt2, WinNuke, Targa


Related Posts :
Distributed denial-of-service attack (DDoS attack)
HOW DOS ATTACKS WORK - BEHIND THE SCENES