DoS (Denial of Service) is probably one of the most popular types of attack today because of its simplicity and the enormous choice of available tools on the internet that can help initiate one.
A DoS attack aims to deny legitimate users access to the targeted system. A DoS attack is a malicious attempt to disrupt the normal functioning of a website, server, or network by overwhelming it with a flood of traffic or requests, making it unresponsive and inaccessible to the users.
The attack can be launched using various techniques, such as flooding the target system with a large number of requests, exploiting vulnerabilities in the system, or using botnets. In some cases, DoS attacks can also be used as a decoy to divert attention from other malicious activities, such as stealing data or installing malware on the target system.
Simple DoS Attacks
There are many different types of DoS attacks that can exhaust a system's resources. The only difference between them is their approach to slow down the system or even crush it.
For example, a TCP SYN flood attack exploits the TCP three-way handshake operation by an attacker sending a large quantity of TCP SYN packets with random source IP addresses to the targeted system. Then, like in the figure above, the victim replies with TCP SYN-ACK for each TCP SYN packet and adds an individual entry inside the connection table.
Because the attacker never completes the third step of the three-way handshake (TCP-ACK), the victim's connection table stays full and keeps all these entries until they expire. As a result, the system becomes unavailable to provide TCP services to legitimate users.
Similar DoS attacks to the TCP SYN flood type are ICMP and UDP flood attacks. Similarly, they cause the victim to spare as many resources as possible to service bogus requests at the expense of valid requests from legitimate users.
An example of a DoS attack would be the famous Ping of Death. The main goal of this attack is to crush a system or a group of many systems working together