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.
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
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.
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 senthttps://e75ee4b2d8d143d34991c63c16560012.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html
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.
DoS (Denial of Service) is an attack used to deny legitimate user’s access to a resource such as accessing a website, network, emails, etc. Distributed Denial of Service (DDoS) is a type of DoS attack that is performed by a number of compromised machines that all target the same victim. It floods the computer network with data packets.
There are numerous DDoS attack tools that can create a distributed denial-of-service attack against a target server. Following is a handpicked list of DDoS Attack Tools, with their popular features and website links. The list contains both open source(free) and commercial(paid) software.
1) LOIC (Low Orbit ION cannon)
LOIC (Low Orbit ION cannon) is open-source software use for DDoS attack. This tool is written in C#. This tool sends HTTP, TCP, and UDP requests to the server.
Features:
LOIC helps you to test the performance of the network.
It enables you to create a DDoS attack against any site that they control.
Loic does not hide an IP address even if the proxy server is not working.
It helps you to perform stress testing to verify the stability of the system.
This software can be used to identify programs that may be used by hackers to attack a computer network.
High Orbit Ion Cannon is a free denial-of-service attack tool. It is designed to attack more than one URLs at the same time. This tool helps you to launch DDoS attacks using HTTP (Hypertext Transfer Protocol).
Features:
You can attack up to 256 websites at once.
It has a counter that helps you to measure the output.
It can be ported over to Linux or Mac OS.
You can choose the number of threads in the current attack.
HOIC enables you to control attacks with low, medium, and high settings.
DDoSIM (DDoS Simulator) is a tool that is used to create a distributed denial-of-service attack against a target server. It is written in C++ and can be used on the Linux operating system.
Features:
This tool indicates the capacity of the server to handle application-specific DDOS attacks.
It enables you to create full TCP connections to the target server.
DDoSIM provides numerous options to perform a network attack.
TCP connections can be flooded on a random network port.
PyLoris is a software product for testing network vulnerability by performing Distributed Denial of Service (DDoS) attack online. It helps you to control poorly manage concurrent connections.
Features:
It provides easy to use GUI (Graphic User Interface).
This tool enables you to attack using HTTP request headers.
It has the latest codebase (collection of source code used to build a particular software system).
You can run PyLoris using Python script.
This tool supports Windows, Mac OS, and Linux.
It provides an advanced option having a limitation of 50 threads, each with a total of 10 connections.
The OWASP (Open Web Application Security Project) HTTP Post software enables you to test your web applications for network performance. It helps you to conduct denial of service from a single machine.
Features:
It allows you to distribute and transmit the tool with others.
You can freely use this tool for commercial purposes.
OWASP HTTP POST helps you to share the result under the license it provides.
This tool enables you to test against the application layer attacks.
RUDY is a short form of R-U-Dead-Yet. It helps you to perform the DDoS attack with ease. It targets cloud applications by starvation of sessions available on the web server.
Features:
This is a simple and easy tool.
It automatically browses the target website and detects embedded web forms.
R-U-Dead-Yet enables you to conduct HTTP DDoS attack using long-form field submission.
This tool provides an interactive console menu.
It automatically identifies form fields for data submission.
Tor’shammer is an application-layer DDoS program. You can use this tool to target web applications and a web server. It performs browser-based internet request that is used to load web pages.
Features:
It allows you to create rich text markup using Markdown (a plain text formatting syntax tool).
Tor’s Hammer automatically converts the URL into links.
This app uses web server resources by creating a vast number of network connections.
You can quickly link other artifacts in your project.
It holds HTTP POST requests and connections for 1000 to 30000 seconds.
DAVOSET is software for committing DDOS attacks via abuse of any website functionality. This command line tool helps you to commit distributed denial of service attacks without any hassle.
Features:
It provides support for cookies.
This tool provides a command-line interface to perform an attack.
DAVOSET can also help you to hit attack using XML external entities (attack against an app that parses XML input).
GoldenEye tool conducts a DDoS attack by sending an HTTP request to the server. It utilizes a KeepAlive message paired with cache-control options to persist socket connection busting.
Features:
This tool consumes all the HTTP/S sockets on the application server for the DDoS attack.
In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connected to the Internet. Denial of service is typically accomplished by flooding the targeted machine or resource with superfluous requests in an attempt to overload systems and prevent some or all legitimate requests from being fulfilled.
In a distributed denial-of-service attack (DDoS attack), the incoming traffic flooding the victim originates from many different sources. This effectively makes it impossible to stop the attack simply by blocking a single source.
A DoS or DDoS attack is analogous to a group of people crowding the entry door of a shop, making it hard for legitimate customers to enter, thus disrupting trade.
Criminal perpetrators of DoS attacks often target sites or services hosted on high-profile web servers such as banks or credit card payment gateways. Revenge, blackmail and can motivate these attacks.
Attack techniques
Attack tools
In cases such as MyDoom and Slowloris the tools are embedded in malware and launch their attacks without the knowledge of the system owner. Stacheldraht is a classic example of a DDoS tool. It uses a layered structure where the attacker uses a client program to connect to handlers which are compromised systems that issue commands to the zombie agents which in turn facilitate the DDoS attack. Agents are compromised via the handlers by the attacker using automated routines to exploit vulnerabilities in programs that accept remote connections running on the targeted remote hosts. Each handler can control up to a thousand agents.
Application-layer attacks
Application-layer attacks employ DoS-causing exploits and can cause server-running software to fill the disk space or consume all available memory or CPU time. Attacks may use specific packet types or connection requests to saturate finite resources by, for example, occupying the maximum number of open connections or filling the victim’s disk space with logs. An attacker with shell-level access to a victim’s computer may slow it until it is unusable or crash it by using a fork bomb. Another kind of application-level DoS attack is XDoS (or XML DoS) which can be controlled by modern web application firewalls (WAFs).
Degradation-of-service attacks
Pulsing zombies are compromised computers that are directed to launch intermittent and short-lived floodings of victim websites with the intent of merely slowing it rather than crashing it. This type of attack, referred to as degradation-of-service, can be more difficult to detect and can disrupt and hamper connection to websites for prolonged periods of time, potentially causing more overall disruption than a denial-of-service attack. Exposure of degradation-of-service attacks is complicated further by the matter of discerning whether the server is really being attacked or is experincing higher than normal legitimate traffic loads.
Denial-of-service Level II
The goal of DoS L2 (possibly DDoS) attack is to cause a launching of a defense mechanism which blocks the network segment from which the attack originated. In case of distributed attack or IP header modification (that depends on the kind of security behavior) it will fully block the attacked network from the Internet, but without system crash.
Distributed DoS attack
A distributed denial-of-service (DDoS) attack occurs when multiple systems flood the bandwidth or resources of a targeted system, usually one or more web servers. Such an attack is often the result of multiple compromised systems (for example, a botnet) flooding the targeted system with traffic. A botnet is a network of zombie computers programmed to receive commands without the owners’ knowledge. When a server is overloaded with connections, new connections can no longer be accepted. The major advantages to an attacker of using a distributed denial-of-service attack are that multiple machines can generate more attack traffic than one machine, multiple attack machines are harder to turn off than one attack machine, and that the behavior of each attack machine can be stealthier, making it harder to track and shut down. These attacker advantages cause challenges for defense mechanisms. For example, merely purchasing more incoming bandwidth than the current volume of the attack might not help, because the attacker might be able to simply add more attack machines. This, after all, will end up completely crashing a website for periods of time.
DDoS extortion
In 2015, DDoS botnets such as DD4BC grew in prominence, taking aim at financial institutions. Cyber-extortionists typically begin with a low-level attack and a warning that a larger attack will be carried out if a ransom is not paid in Bitcoin. Security experts recommend targeted websites to not pay the ransom. The attackers tend to get into an extended extortion scheme once they recognize that the target is ready to pay.
HTTP slow POST DoS attack
First discovered in 2009, the HTTP slow POST attack sends a complete, legitimate HTTP POST header, which includes a ‘Content-Length’ field to specify the size of the message body to follow. However, the attacker then proceeds to send the actual message body at an extremely slow rate. Due to the entire message being correct and complete, the target server will attempt to obey the ‘Content-Length’ field in the header, and wait for the entire body of the message to be transmitted, which can take a very long time. The attacker establishes hundreds or even thousands of such connections until all resources for incoming connections on the server (the victim) are used up, hence making any further (including legitimate) connections impossible until all data has been sent. It is notable that unlike many other (D)DoS attacks, which try to subdue the server by overloading its network or CPU, an HTTP slow POST attack targets the logical resources of the victim, which means the victim would still have enough network bandwidth and processing power to operate. Further combined with the fact that will, by default, accept requests up to 2GB in size, this attack can be particularly powerful. HTTP slow POST attacks are difficult to differentiate from legitimate connections and are therefore able to bypass some protection systems. OWASP, an open source web application security project, released a tool to test the security of servers against this type of attacks.
Challenge Collapsar (CC) attack
A Challenge Collapsar (CC) attack is an attack that standard HTTP requests are sent to a targeted web server frequently, in which the Uniform Resource Identifiers (URIs) require complicated time-consuming algorithms or database operations, in order to exhaust the resources of the targeted web server.
In 2004, a Chinese hacker nicknamed KiKi invented a hacking tool to send these kinds of requests to attack a NSFOCUS firewall named “Collapsar”, and thus the hacking tool was known as “Challenge Collapsar”, or CC for short. Consequently, this type of attack got the name “CC attack”.
Internet Control Message Protocol (ICMP) flood
A smurf attack relies on misconfigured network devices that allow packets to be sent to all computer hosts on a particular network via the broadcast address of the network, rather than a specific machine. The attacker will send large numbers of IP packets with the source address faked to appear to be the address of the victim. Most devices on a network will, by default, respond to this by sending a reply to the source IP address. If the number of machines on the network that receive and respond to these packets is very large, the victim’s computer will be flooded with traffic. This overloads the victim computer and can even make it unusable during such attack.
Ping flood is based on sending the victim an overwhelming number of ping packets, usually using the “ping” command from Unix-like hosts (the -t flag on Windows systems is much less capable of overwhelming a target, also the -l (size) flag does not allow sent packet size greater than 65500 in Windows). It is very simple to launch, the primary requirement being access to greater bandwidth than the victim.
Ping of death is based on sending the victim a malformed ping packet, which will lead to a system crash on a vulnerable system.
The BlackNurse attack is an example of an attack taking advantage of the required Destination Port Unreachable ICMP packets.
Nuke
A Nuke is an old denial-of-service attack against computer networks consisting of fragmented or otherwise invalid ICMP packets sent to the target, achieved by using a modified ping utility to repeatedly send this corrupt data, thus slowing down the affected computer until it comes to a complete stop.[52]
A specific example of a nuke attack that gained some prominence is the WinNuke, which exploited the vulnerability in the NetBIOS handler in Windows 95. A string of out-of-band data was sent to TCP port 139 of the victim’s machine, causing it to lock up and display a Blue Screen of Death (BSOD).
Peer-to-peer attacks
Attackers have found a way to exploit a number of bugs in peer-to-peer servers to initiate DDoS attacks. The most aggressive of these peer-to-peer-DDoS attacks exploits DC++. With peer-to-peer there is no botnet and the attacker does not have to communicate with the clients it subverts. Instead, the attacker acts as a “puppet master,” instructing clients of large peer-to-peer file sharing hubs to disconnect from their peer-to-peer network and to connect to the victim’s website instead.
Permanent denial-of-service attacks
Permanent denial-of-service (PDoS), also known loosely as phlashing, is an attack that damages a system so badly that it requires replacement or reinstallation of hardware. Unlike the distributed denial-of-service attack, a PDoS attack exploits security flaws which allow remote administration on the management interfaces of the victim’s hardware, such as routers, printers, or other networking hardware. The attacker uses these vulnerabilities to replace a device’s firmware with a modified, corrupt, or defective firmware image—a process which when done legitimately is known as flashing. This therefore “bricks” the device, rendering it unusable for its original purpose until it can be repaired or replaced.
The PDoS is a pure hardware targeted attack which can be much faster and requires fewer resources than using a botnet or a root/vserver in a DDoS attack. Because of these features, and the potential and high probability of security exploits on Network Enabled Embedded Devices (NEEDs), this technique has come to the attention of numerous hacking communities. BrickerBot, a piece of malware that targeted IoT devices, used PDoS attacks to disable its targets.
PhlashDance is a tool created by Rich Smith (an employee of Hewlett-Packard’s Systems Security Lab) used to detect and demonstrate PDoS vulnerabilities at the 2008 EUSecWest Applied Security Conference in London.
Reflected / spoofed attack
A distributed denial-of-service attack may involve sending forged requests of some type to a very large number of computers that will reply to the requests. Using Internet Protocol address spoofing, the source address is set to that of the targeted victim, which means all the replies will go to (and flood) the target. (This reflected attack form is sometimes called a “DRDOS”.)
ICMP Echo Request attacks (Smurf attack) can be considered one form of reflected attack, as the flooding host(s) send Echo Requests to the broadcast addresses of mis-configured networks, thereby enticing hosts to send Echo Reply packets to the victim. Some early DDoS programs implemented a distributed form of this attack.
Mirai botnet
This attack works by using a worm to infect hundreds of thousands of IoT devices across the internet. The worm propagates through networks and systems taking control of poorly protected IoT devices such as thermostats, Wi-Fi enabled clocks and washing machines.W the device becomes enslaved usually the owner or user will have no immediate indication. The IoT device itself is not the direct target of the attack, it is used as a part of a larger attack. These newly enslaved devices are called slaves or bots. Once the hacker has acquired the desired number of bots, they instruct the bots to try to contact an ISP. In October 2016, a Mirai botnet attacked Dyn which is the ISP for sites such as Twitter, Netflix, etc. Assoon as this occurred, these websites were all unreachable for several hours. This type of attack is not physically damaging, but it will certainly be costly for any large internet companies that get attacked.
R-U-Dead-Yet? (RUDY)
RUDY attack targets web applications by starvation of available sessions on the web server. Much like Slowloris, RUDY keeps sessions at halt using never-ending POST transmissions and sending an arbitrarily large content-length header value.
SACK Panic
Manipulating maximum segment size and selective acknowledgement (SACK) it may be used by a remote peer to cause a denial of service by an integer overflow in the Linux kernel, causing even a Kernel panic. Jonathan Looney discovered CVE-2019-11477, CVE-2019-11478, CVE-2019-11479 on June 17, 2019.
Shrew attack
The shrew attack is a denial-of-service attack on the Transmission Control Protocol where the attacker employs man-in-the-middle techniques. It uses short synchronized bursts of traffic to disrupt TCP connections on the same link, by exploiting a weakness in TCP’s re-transmission timeout mechanism.[73]
Slow Read attack
A slow read attack sends legitimate application layer requests, but reads responses very slowly, thus trying to exhaust the server’s connection pool. It is achieved by advertising a very small number for the TCP Receive Window size, and at the same time emptying clients’ TCP receive buffer slowly, which causes a very low data flow rate.
A sophisticated low-bandwidth DDoS attack is a form of DoS that uses less traffic and increases their effectiveness by aiming at a weak point in the victim’s system design, i.e., the attacker sends traffic consisting of complicated requests to the system. Essentially, a sophisticated DDoS attack is lower in cost due to its use of less traffic, is smaller in size making it more difficult to identify, and it has the ability to hurt systems which are protected by flow control mechanisms.
(S)SYN flood
A SYN flood occurs when a host sends a flood of TCP/SYN packets, often with a forged sender address. Each of these packets are handled like a connection request, causing the server to spawn a half-open connection, by sending back a TCP/SYN-ACK packet (Acknowledge), and waiting for a packet in response from the sender address (response to the ACK Packet). However, because the sender address is forged, the response never comes. These half-open connections saturate the number of available connections the server can make, keeping it from responding to legitimate requests until after the attack ends.
Teardrop attacks
A teardrop attack involves sending mangled IP fragments with overlapping, oversized payloads to the target machine. This can crash various operating systems because of a bug in their TCP/IP fragmentation re-assembly code. Windows 3.1x, Windows 95 and Windows NT operating systems, as well as versions of Linux prior to versions 2.0.32 and 2.1.63 are vulnerable to this attack.
(Although in September 2009, a vulnerability in Windows Vista was referred to as a “teardrop attack”, this targeted SMB2 which is a higher layer than the TCP packets that teardrop used).
One of the fields in an IP header is the “fragment offset” field, indicating the starting position, or offset, of the data contained in a fragmented packet relative to the data in the original packet. If the sum of the offset and size of one fragmented packet differs from that of the next fragmented packet, the packets overlap. When this happens, a server vulnerable to teardrop attacks is unable to reassemble the packets – resulting in a denial-of-service condition.
Telephony denial-of-service (TDoS)
Voice over IP has made abusive origination of large numbers of telephone voice calls inexpensive and readily automated while permitting call origins to be misrepresented through caller ID spoofing.
TTL expiry attack
It takes more router resources to drop a packet with a TTL value of 1 or less than it does to forward a packet with higher TTL value. When a packet is dropped due to TTL expiry, the router CPU must generate and send an ICMP time exceeded response. Generating many of these responses can overload the router’s CPU.
UPnP attack
This attack uses an existing vulnerability in Universal Plug and Play (UPnP) protocol to get around a considerable amount of the present defense methods and flood a target’s network and servers. The attack is based on a DNS amplification technique, but the attack mechanism is a UPnP router which forwards requests from one outer source to another disregarding UPnP behavior rules. Using the UPnP router returns the data on an unexpected UDP port from a bogus IP address, making it harder to take simple action to shut down the traffic flood. According to the Imperva researchers, the most effective way to stop this attack is for companies to lock down UPnP routers.
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