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What is DoS Attack?

DOS is an attack used to deny legitimate users access to a resource such as accessing a website, network, emails, etc. or making it extremely slow. DoS is the acronym for Denial of Service. This type of attack is usually implemented by hitting the target resource such as a web server with too many requests at the same time. This results in the server failing to respond to all the requests. The effect of this can either be crashing the servers or slowing them down.

Cutting off some business from the internet can lead to significant loss of business or money. The internet and computer networks power a lot of businesses. Some organizations such as payment gateways, e-commerce sites entirely depend on the internet to do business.

In this tutorial, we will introduce you to what denial of service attack is, how it is performed and how you can protect against such attacks.

Topics covered in this tutorial

• Types of Dos Attacks
• How DoS attacks work
• DoS attack tools
• DoS Protection: Prevent an attack
• Hacking Activity: Ping of Death
• Hacking Activity: Launch a DOS attack

Types of Dos Attacks

There are two types of Dos attacks namely;

• DoS– this type of attack is performed by a single host
• Distributed DoS– this type of attack is performed by a number of compromised machines that all target the same victim. It floods the network with data packets.

How DoS attacks work

Let's look at how DoS attacks are performed and the techniques used. We will look at five common types of attacks.

Ping of Death

The ping command is usually used to test the availability of a network resource. It works by sending small data packets to the network resource. The ping of death takes advantage of this and sends data packets above the maximum limit (65,536 bytes) that TCP/IP allows. TCP/IP fragmentation breaks the packets into small chunks that are sent to the server. Since the sent data packages are larger than what the server can handle, the server can freeze, reboot, or crash.

Smurf

This type of attack uses large amounts of Internet Control Message Protocol (ICMP) ping traffic target at an Internet Broadcast Address. The reply IP address is spoofed to that of the intended victim. All the replies are sent to the victim instead of the IP used for the pings. Since a single Internet Broadcast Address can support a maximum of 255 hosts, a smurf attack amplifies a single ping 255 times.  The effect of this is slowing down the network to a point where it is impossible to use it.

Buffer overflow

A buffer is a temporal storage location in RAM that is used to hold data so that the CPU can manipulate it before writing it back to the disc. Buffers have a size limit. This type of attack loads the buffer with more data that it can hold. This causes the buffer to overflow and corrupt the data it holds. An example of a buffer overflow is sending emails with file names that have 256 characters.

Teardrop

This type of attack uses larger data packets. TCP/IP breaks them into fragments that are assembled on the receiving host. The attacker manipulates the packets as they are sent so that they overlap each other. This can cause the intended victim to crash as it tries to re-assemble the packets.

SYN attack

SYN is a short form for Synchronize. This type of attack takes advantage of the three-way handshake to establish communication using TCP. SYN attack works by flooding the victim with incomplete SYN messages. This causes the victim machine to allocate memory resources that are never used and deny access to legitimate users.

DoS attack tools

The following are some of the tools that can be used to perform DoS attacks.

• Nemesy– this tool can be used to generate random packets. It works on windows. This tool can be downloaded from http://packetstormsecurity.com/files/25599/nemesy13.zip.html . Due to the nature of the program, if you have an antivirus, it will most likely be detected as a virus.
• Land and LaTierra– this tool can be used for IP spoofing and opening TCP connections
• Blast– this tool can be downloaded from http://www.opencomm.co.uk/products/blast/features.php
• Panther- this tool can be used to flood a victim's network with UDP packets.
• Botnets– these are multitudes of compromised computers on the Internet that can be used to perform a distributed denial of service attack.

DoS Protection: Prevent an attack

An organization can adopt the following policy to protect itself against Denial of Service attacks.

• Attacks such as SYN flooding take advantage of bugs in the operating system. Installing security patches can help reduce the chances of such attacks.
• Intrusion detection systems can also be used to identify and even stop illegal activities
• Firewalls can be used to stop simple DoS attacks by blocking all traffic coming from an attacker by identifying his IP.
• Routers can be configured via the Access Control List to limit access to the network and drop suspected illegal traffic.

Hacking Activity: Ping of Death

We will assume you are using Windows for this exercise. We will also assume that you have at least two computers that are on the same network. DOS attacks are illegal on networks that you are not authorized to do so. This is why you will need to setup your own network for this exercise.

Open the command prompt on the target computer

Enter the command ipconfig. You will get results similar to the ones shown below

For this example, we are using Mobile Broadband connection details. Take note of the IP address. Note: for this example to be more effective, and you must use a LAN network.

 Switch to the computer that you want to use for the attack and open the command prompt

We will ping our victim computer with infinite data packets of 65500

Enter the following command

ping 10.128.131.108 –t |65500

HERE,

• "ping" sends the data packets to the victim
• "10.128.131.108" is the IP address of the victim
• "-t" means the data packets should be sent until the program is stopped
• "-l" specifies the data load to be sent to the victim

You will get results similar to the ones shown below

Flooding the target computer with data packets doesn't have much effect on the victim. In order for the attack to be more effective, you should attack the target computer with pings from more than one computer.

The above attack can be used to attacker routers, web servers etc.

If you want to see the effects of the attack on the target computer, you can open the task manager and view the network activities.

• Right click on the taskbar
• Select start task manager
• Click on the network tab
• You will get results similar to the following

If the attack is successful, you should be able to see increased network activities.

 

Hacking Activity: Launch a DOS attack

In this practical scenario, we are going to use Nemesy to generate data packets and flood the target computer, router or server.

As stated above, Nemesy will be detected as an illegal program by your anti-virus. You will have to disable the anti-virus for this exercise.

• Download Nemesy from http://packetstormsecurity.com/files/25599/nemesy13.zip.html
• Unzip it and run the program Nemesy.exe
• You will get the following interface

Enter the target IP address, in this example; we have used the target IP we used in the above example.

HERE,

• 0 as the number of packets means infinity. You can set it to the desired number if you do not want to send, infinity data packets
• The size field specifies the data bytes to be sent and the delay specifies the time interval in milliseconds.

 

Click on send button

You should be able to see the following results

The title bar will show you the number of packets sent

Click on halt button to stop the program from sending data packets.

You can monitor the task manager of the target computer to see the network activities.

Summary

• A denial of service attack's intent is to deny legitimate users access to a resource such as a network, server etc.
• There are two types of attacks, denial of service and distributed denial of service.
• A denial of service attack can be carried out using SYN Flooding, Ping of Death, Teardrop, Smurf or buffer overflow
• Security patches for operating systems, router configuration, firewalls and intrusion detection systems can be used to protect against denial of service attacks.

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After the devastating loss of Rascal, I went back to training out on Route 2 with Lucky. There was no way a mere Metapod was going to stand up to Gym Leader Brock. I had confidence that Rascal, Nibbles and Kiwi would help me earn the Boulder Badge, but without Rascal my confidence faltered. It took us a few days, but eventually Lucky sprouted wings and evolved into Butterfree, a significant improvement over the lovably little lump of a Pokémon he was as Metapod. I did not neglect Kiwi and Nibbles during this time, either, but their progress was a bit less important.
Once Lucky had evolved, I spent what little money I had on a couple of potions at the PokéMart. Although they were expensive, I would not let another Pokémon fall in the Pewter City Gym. I absolutely would not. My nerves were shot as I stepped into the gym for the second time. I remember I was sweating and shaking just thinking about facing Brock. I saw the Junior Trainer who had bested my poor Rascal. He gave me an approving nod, but it did little to improve my disposition. Brock stood at the far end of the gym and beckoned me forward. He had seen my fight with the Junior Trainer several days ago and was eager to face me.

I clenched my jaw tightly as I threw out my first Pokémon. Kiwi met Brock's Geodude face-to-face in the gym's arena. We wasted no time kicking up as much dust as possible to obscure Geodude's vision. Brock had Geodude spend most of its time curling up into a defensive ball, but every now and then it lashed out with a tackle that it simply couldn't land on Kiwi. When I felt it's accuracy was sufficiently incapacitated, I withdrew Kiwi and used Nibble to wear down the Geodude slowly but surely. The Geodude was powerless in the dust Kiwi's sand-attack had kicked up and against Nibbles relentless tackling.
Then Brock threw out his champion, the Onix. I tossed Kiwi back into the ring hoping to repeat our earlier performance on Geodude. Kiwi kicked up as much sand as he could, but Onix still managed to land a lucky strike on him. It hurt Kiwi enough to discourage me from keeping Kiwi on the field any longer. Nibbles was sent out while Onix merely bided his time. I knew immediately that any attacks on Onix while in this defensive state would be unleashed twofold onto its attacker. Your only choices are to crush it swiftly, which is difficult against a rock hard Pokémon like Onix, or to wait it out.
Nibbles began to stare down his opponent while it remained in its defensive posture. Slowly this would lower the Onix's defenses and leave it vulnerable to a massive strike. Eventually, Nibbles was exchanged for Lucky who covered the Onix in its string shot while it continued to wait for our attacks. Feeling safer, Kiwi returned to the battle to continue whipping up sand into Onix's face. Then as soon as Onix released its defensive posturing, Kiwi slammed it with a gust from his wings and knocked the Onix to the floor.
That was how I won my first badge in the great region of Kanto.

Brock was impressed and clasped me firmly on the back with a great slap of his hand. He knew about Rascal, of course, and was pleased at my stance on training. He liked how patient and defensive I was and as a reward not only gave me a handsome sum of PokéDollars, but a Technical Machine that would teach certain eligible Pokémon his Onix's signature technique of biding time and waiting for the counter strike. This strategy didn't really work out well for Brock that day, so I wasn't sure how I would incorporate it on to a team that I intended to take as few hits as possible. I didn't want to be rude, though, so I graciously accepted the TM #34 and the Boulder Badge.
I was now officially on the road to challenge the Indigo Plateau League. I really hadn't come to Kanto expecting to do something quite that dramatic, but I was slowly being pushed in that direction. Professor Oak had prompted me to take this journey and running into Wolf made me question what the journey really meant to me personally. The encounter with the snarky trainer in Viridian City helped me shape my personal goals and encouraged me to challenge the gyms to seek reputation and understanding in the world of Pokémon training. Now, I had my first badge pinned proudly to my backpack and I was on my way to the next adventure — with considerably more money to spend thanks to my winnings.

Current Team:
Attacks in Blue are recently learned.