What Is Denial of Service (DoS) Attack?

If you are working in the field of computer networks or an enthusiast in the field of network security, you are sure to have come across the term Denial of Service attack which is simply referred to as “DoS attack”. Today, this is one of the most common types of network attacks carried out on the Internet. In this post, We will try to explain DoS attack, its variants and methods involved to carry out the same in an easily understandable manner.

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What is a DOS Attack?

Denial of Service or DoS attack is a type of network attack designed to flood the target network or machine with a large amount of useless traffic so as to overload it and eventually bring it down to its knees. The main intention behind DoS attack is to make the services running on the target machine (such as a website) temporarily unavailable to its intended users. DoS attacks are usually carried out on web servers that host vital services such as banking, e-commerce or credit card processing.
DDoS (Distributed Denial of Service)
A common variant of DOS attack known as DDoS attack has become quite popular in the recent days as it is more powerful and hard to detect. A typical DoS attack has a single place of origin while a DDoS attack originates from multiple IP addresses distributed across two or more different network.

Protection Against DoS/DDoS Attacks:

DoS attacks can easily be handled by blacklisting the target IP (or range of IPs) that are found to be making too many requests/connections (in an unnatural way) to the server. However, DDoS attacks are complicated as the incoming requests seem more natural and distributed. In this case it is hard to find the difference between the genuine and malicious traffic. Taking an action at the firewall level to blacklist suspected IPs may result in false positives and therefore may affect the genuine traffic as well.

Methods Involved in DoS Attack

The following are some of the commonly employed methods in carrying out a DoS attack:
  • SYN Flood Attack
  • Ping Flood Attack (Ping of Death)
  • Teardrop Attack
  • Peer-to-Peer Attacks

1. SYN Flood Attack

syn-ddos-attack

SYN flooding is an attack vector for conducting a denial-of-service (DoS) attack on a computer server.
The attack involves having a client repeatedly send SYN (synchronization) packets to every port on a server, using fake IP addresses. When an attack begins, the server sees the equivalent of multiple attempts to establish communications. The server responds to each attempt with a SYN/ACK (synchronization acknowledged) packet from each open port, and with a RST (reset) packet from each closed port.

2. Ping Flood Attack (Ping of Death)

DDoS-Attack-ping

Ping of Death (a.k.a. PoD) is a type of Denial of Service (DoS) attack in which an attacker attempts to crash, destabilize, or freeze the targeted computer or service by sending malformed or oversized packets using a simple ping command.
While PoD attacks exploit legacy weaknesses which may have been patched in target systems. However, in an unpatched systems, the attack is still relevant and dangerous. Recently, a new type of PoD attack has become popular. This attack, commonly known as a Ping flood, the targeted system is hit with ICMP packets sent rapidly via ping without waiting for replies.

3. Teardrop Attack

DDoS-Attack

A teardrop attack is a denial of service (DoS) attack conducted by targeting TCP/IP fragmentation reassembly codes. This attack causes fragmented packets to overlap one another on the host receipt; the host attempts to reconstruct them during the process but fails. Gigantic payloads are sent to the machine that is being targeted, causing system crashes.
While much more popular on older versions of Windows, the teardrop attack is also possible on Windows 7 and Windows Vista machines that have SMB enabled. The driver vulnerability on the latter two operating systems was noted in 2009, but Windows 2000 and Windows XP are not vulnerable to this type of teardrop attack, which hones in on TCP ports 139 and 445 on the firewalls of the SMB-enabled machines. If users don’t have patches to protect against this DoS attack, SMBv2 should be disabled, as recommended by Microsoft, and ports 139 and 445 should be blocked.

4. Peer-to-Peer Attacks

DDoS-Attack-peer2peer

Peer relationship exploitation can be defined in several ways. First, it can be the exploitation of transitive trust relationships created by peer-networking so as to expand privileges to the transitive closure of peer trust. It can also be defined in less technical terms. Exploitation can be when an insider uses the security access of colleagues to gain access to unauthorized information.  This can include physical access or information access.

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