Denial of Service Accepting early data exposes a server to potential denial of service through the replay of requests that are expensive to handle. A server that is under load SHOULD prefer rejecting TLS early data as a whole rather than accepting early data and selectively processing requests. Jul 03, 2019 A vulnerability in the Session Initiation Protocol (SIP) protocol implementation of Cisco Unified Communications Manager and Unified Communications Manager Session Management Edition could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. The vulnerability is due to insufficient validation of input SIP traffic. An attacker could exploit this vulnerability.

A Denial of Service (DoS) attack is designed to cause service outages. These attacks can easily cost an organization a significant amount in damages and wasted resources, even if the attacker does not demand a ransom to stop the attack. A number of different free DDoS tools exist, making it cheap and easy for even unsophisticated attackers to use this attack technique.

What is a denial-of-service attack?

A DoS attack is any attack that is designed to take a system offline or make it unavailable to legitimate users. The goal of the attack could be to hurt the target organization, extort a ransom to allow services to be restored or cover up another attack.

DoS attacks can take advantage of a number of different vulnerabilities within a computer system. Buffer overflow vulnerabilities and other programming flaws can be exploited to cause a segmentation fault or other error that causes a program to crash.

However, the most common method of performing a DoS attack is to take advantage of bottlenecks within a computing system. Every component of a system has a maximum amount of traffic, data, connections and so on that it is capable of processing, and the entire system is limited by the component with the lowest threshold. Most DoS attacks are designed to exceed this maximum capacity, making it impossible for the system to process legitimate user requests.

DoS attacks can be performed in multiple different ways. Examples of common attack techniques include:

• Volumetric attacks: Network connections and network interface cards (NICs) have set bandwidth limitations. Volumetric attacks attempt to overwhelm these systems by sending more data than they can handle. These attacks may be composed of a massive number of small packets or a smaller number of very large ones.
• Protocol-level attacks: Computers have a set number of TCP and UDP port numbers allocated and cannot handle a new connection if no port is available. Protocol-level attacks attempt to consume all of a computer’s available connections, making it incapable of accepting new connections.
• Application-layer attacks: Applications communicating over the network need to be capable of processing the requests that they receive. In many cases, an application’s thresholds are much lower than the infrastructure that it runs on. By sending many legitimate requests to an application, an attacker can consume all of its available resources and make it unavailable to legitimate users.

DDoS or distributed denial-of-service attack

DoS attacks are designed to overwhelm a service with more traffic than it can handle. However, this assumes that the attacker has the resources necessary to achieve this.

Distributed DoS (DDoS) attacks are designed to ensure that the target is overwhelmed by taking a many-to-one approach to the attack. Instead of using a single machine to perform an attack, the attacker uses a botnet.

This botnet is composed of many attacker-controlled machines, including compromised computers, leased cloud infrastructure and more. Each of these machines is instructed to send some traffic to the target service. By taking advantage of its greater numbers, a DDoS botnet can take down any unprotected service, even if the target has more network bandwidth and better computers than the attacker.

Free DoS attacking tools

It’s possible for an attacker to write custom software to perform a DoS attack or malware to perform a DDoS attack, and many DDoS websites offer DDoS-as-a-Service. For penetration testers wishing to perform their attacks independently but don’t want to write their own tools, a number of free DoS attack tools exist.

1. LOIC (Low Orbit Ion Cannon)

LOIC is one of the most popular DoS attacking tools freely available on the internet. The famous hacking group Anonymous has not only used the tool, but also requested internet users to join their DDoS attacks via IRC.

LOIC can be used by a single user to perform a DoS attack on small servers. This tool is really easy to use, even for a beginner. This tool performs a DoS attack by sending UDP, TCP or HTTP requests to the victim server. You only need to know the URL or IP address of the server, and the tool will do the rest.

Image 1: Low Orbit Ion Cannon

You can see a snapshot of the tool above. Enter the URL or IP address, and then select the attack parameters. If you are not sure about what settings to use, you can leave the defaults. When you are done with everything, click on the big button saying “IMMA CHARGIN MAH LAZER”, and it will start attacking the target server.

This tool also has a HIVEMIND mode. It lets attackers control remote LOIC systems to perform a DDoS attack. This feature is used to control all other computers in your zombie network. This tool can be used for both DoS attacks and DDoS attacks against any website or server.

The most important thing you should know is that LOIC does nothing to hide your IP address. If you are planning to use LOIC to perform a DoS attack, think again. Using a proxy will not help you because it will hit the proxy server not the target server. This tool should only be used for testing the resiliency of your own systems against DoS and DDoS attacks.

2. XOIC

XOIC is another nice DoS attacking tool. It performs a DoS attack against any server if the user can provide an IP address, a target port, and a protocol to use in the attack. Developers of XOIC claim that XOIC is more powerful than LOIC in many ways. Like LOIC, it comes with an easy-to-use GUI, so a beginner can easily use this tool to perform attacks.

Image 2: XOIC

In general, the tool comes with three attacking modes. The first one, known as test mode, is very basic. The second is normal DoS attack mode. The last one is a DoS attack mode that comes with a TCP/HTTP/UDP/ICMP Message.

Download XOIC here.

3. HULK (HTTP Unbearable Load King)

HULK is another nice DoS attacking tool that generates a unique request for each and every request to the web server, making it more difficult for the server to detect patterns within the attack. This is only one of the ways in which HULK eliminates patterns within its attacks.

It has a list of known user agents to use randomly with requests. It also uses referrer forgery and can bypass caching engines; thus, it directly hits the server’s resource pool.

Download HULK here.

4. DDoSIM — Layer 7 DDoS Simulator

DDoSIM is another popular DoS attacking tool. As the name suggests, it is used to perform DDoS attacks by simulating several zombie hosts. All zombie hosts create full TCP connections to the target server.

This tool is written in C++ and runs on Linux systems.

These are main features of DDoSIM

• Simulates several zombies in attack
• Random IP addresses
• TCP-connection-based attacks
• Application-layer DDoS attacks
• HTTP DDoS with valid requests
• HTTP DDoS with invalid requests (similar to a DC++ attack)
• SMTP DDoS
• TCP connection flood on random port

Download DDoSIM here.

Read more about this tool here.

5. R-U-Dead-Yet

R-U-Dead-Yet is a HTTP POST DoS attack tool. For short, it is also known as RUDY. It performs a DoS attack with a long form field submission via the POST method. This tool comes with an interactive console menu. It detects forms on a given URL and lets users select which forms and fields should be used for a POST-based DoS attack.

Download RUDY here.

6. Tor’s Hammer

Tor’s Hammer is a nice DoS testing tool written in Python. It performs slow-rate attacks using HTTP POST requests.

This tool has an extra advantage: It can be run through a TOR network to be anonymous while performing the attack. It is an effective tool that can kill Apache or IIS servers in a few seconds.

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Download TOR’s Hammer here.

7. PyLoris

PyLoris is said to be a testing tool for servers. It can be used to perform DoS attacks on a service. This tool can utilize SOCKS proxies and SSL connections to perform a DoS attack on a server. It can target various protocols, including HTTP, FTP, SMTP, IMAP and Telnet.

The latest version of the tool comes with a simple and easy-to-use GUI. Unlike other traditional DoS attacking tools, this tool directly hits the service.

Download PyLoris here.

8. OWASP Switchblade (formerly DoS HTTP POST)

OWASP Switchblade is another nice tool to perform DoS attacks. You can use this tool to check whether or not your web server is able to defend against DoS attacks. Not only for defense, it can also be used to perform DoS attacks against a website during a Red Team exercise.

Download Switchblade here.

9. DAVOSET

DAVOSET is yet another nice tool for performing DDoS attacks. The latest version of the tool has added support for cookies along with many other features. You can download DAVOSET for free from Packetstormsecurity.

Download DavoSET here.

10. GoldenEye HTTP Denial of Service Tool

GoldenEye is another simple but effective DoS attacking tool. It was developed in Python for testing DoS attacks.

Download GoldenEye here.

Detection and prevention of denial-of-service attack

A successful DoS attack can cause significant damage to an organization’s operations. For this reason, it is important to have strategies and solutions in place to protect against them.

The first step in protecting against DoS attacks is minimizing the attack surface. One way to accomplish this is to deploy a network firewall with a restrictive allow/block list. This limits inbound traffic to protocols legitimately used by applications within the organization’s network and blocks any other traffic at the network border.

Anti-DoS tools are specialized solutions designed to identify and filter out attack traffic before it reaches the target service. This is accomplished by identifying features of the malicious traffic that differ from legitimate traffic. However, the increasing sophistication of DoS attacks makes this more difficult to perform.

The DDoS threat can also be decreased by denying attackers’ access to devices for use in their attacks. Botnets are commonly composed of computers, Internet of Things (IoT), and mobile devices that are compromised due to poor password security, lack of patching, or malware infections. Using strong passwords, installing security updates and using a trusted antivirus on all systems can help to limit the size of the botnets used in DDoS attacks.

Conclusion

Denial-of-service attacks can knock an organization’s systems offline and waste valuable resources on malicious traffic. This incurs significant costs for the target, even if the attacker doesn’t demand a ransom to stop their attacks.

The wide variety of free tools make it cheap and easy for cybercriminals to perform DoS and DDoS attacks, so every organization should have systems in place to protect against them. This is especially true as the growth of the Internet of Things and cloud computing make enterprise-scale attacks cheaper for attackers to perform.

Read more about DoS

Updated: October 30, 2020

Distributed Denial of Service (DDoS) attacks are now everyday occurrences. Whether you’re a small non-profit or a huge multinational conglomerate, your online services—email, websites, anything that faces the internet—can be slowed or completely stopped by a DDoS attack. Moreover, DDoS attacks are sometimes used to distract your cybersecurity operations while other criminal activity, such as data theft or network infiltration, is underway.

DDoS are Attacks Getting Bigger, More Frequent

The first known Distributed Denial of Service attack occurred in 1996 when Panix, now one of the oldest internet service providers, was knocked offline for several days by a SYN flood, a technique that has become a classic DDoS attack. Over the next few years DDoS attacks became common and Cisco predicts that the total number of DDoS attacks will double from the 7.9 million seen in 2018 to something over 15 million by 2023.

Total DDoS Attacks

Figure 1. Cisco’s analysis of DDoS total attacks history and predictions.

But it’s not just the number of DDoS attacks that are increasing. The bad guys are creating ever bigger botnets – the armies of hacked devices that are used to generate DDoS traffic. As the botnets get bigger, the scale of DDoS attacks is also increasing. A Distributed Denial of Service attack of one gigabit per second is enough to knock most organizations off the internet but we’re now seeing peak attack sizes in excess of one terabit per second generated by hundreds of thousands or even millions of suborned devices. For more background about what’s technically involved in a Distributed Denial of Service attack, see our post What is a DDoS Attack?, and our video WHO, WHAT, WHY, WHERE of DDoS Attacks.

The Cost of DDoS Attacks

Given that IT services downtime costs companies anywhere from $300,000 to over $1,000,000 per hour, you can see that the financial hit from even a short DDoS attack could seriously damage your bottom line. To understand what impact a Distributed Denial of Service attack could have on your organization and your cybersecurity planning, please see our white paper How to Analyze the Business Impact of DDoS Attacks.

The Top-Five Most Famous DDoS Attacks (for Now)

To give you insight into what these attacks are like “in the wild,” we’re going to take a look at some of the most notable DDoS attacks to date. Our choices include some DDoS attacks that are famous for their sheer scale while our others are because of their impact and consequences.

1. The Google Attack, 2017

On October 16, 2020, Google’s Threat Analysis Group (TAG) posted a blog update discussing how the threats and threat actors are changing their tactics due to the 2020 U.S. election. At the end of the post, the company snuck in a note:

In 2017, our Security Reliability Engineering team measured a record-breaking UDP amplification attack sourced out of several Chinese ISPs (ASNs 4134, 4837, 58453, and 9394), which remains the largest bandwidth attack of which we are aware.

Launched from three Chinese ISPs, the attack on thousands of Google’s IP addresses lasted for six months and peaked at a breath-taking 2.5 Tbps. Damian Menscher, a Security Reliability Engineer at Google, wrote:

The attacker used several networks to spoof 167 Mpps (millions of packets per second) to 180,000 exposed CLDAP, DNS, and SMTP servers, which would then send large responses to us. This demonstrates the volumes a well-resourced attacker can achieve. This was four times larger than the record-breaking 623 Gbps attack from the Mirai botnet a year earlier.

2. The AWS DDoS Attack in 2020

Amazon Web Services, the 800-pound gorilla of everything cloud computing, was hit by a gigantic DDoS attack in February 2020. This was the most extreme recent DDoS attack ever and it targeted an unidentified AWS customer using a technique called Connectionless Lightweight Directory Access Protocol (CLDAP) Reflection. This technique relies on vulnerable third-party CLDAP servers and amplifies the amount of data sent to the victim’s IP address by 56 to 70 times. The attack lasted for three days and peaked at an astounding 2.3 terabytes per second.

Why the AWS Attack Matters

While the disruption caused by the AWS DDoS Attack was far less severe than it could have been, the sheer scale of the attack and the implications for AWS hosting customers potentially losing revenue and suffering brand damage are significant.

3. The Mirai Krebs and OVH DDoS Attacks in 2016

On September 20, 2016, the blog of cybersecurity expert Brian Krebs was assaulted by a DDoS attack in excess of 620 Gbps, which at the time, was the largest attack ever seen. Krebs’ site had been attacked before. Krebs had recorded 269 DDoS attacks since July 2012, but this attack was almost three times bigger than anything his site or, for that matter, the internet had seen before.

The source of the attack was the Mirai botnet, which, at its peak later that year, consisted of more than 600,000 compromised Internet of Things (IoT) devices such as IP cameras, home routers, and video players. The Mirai botnet had been discovered in August that same year but the attack on Krebs’ blog was its first big outing.

The next Mirai botnet attack on September 19 targeted one of the largest European hosting providers, OVH, which hosts roughly 18 million applications for over one million clients. This attack was on a single undisclosed OVH customer and driven by an estimated 145,000 bots, generating a traffic load of up to 1.1 terabits per second, and lasted about seven days. But OVH was not to be the last Mirai botnet victim in 2016 … please see the next section.

Why the Mirai Krebs and OVH Attacks Matter

The Mirai botnet was a significant step up in how powerful a DDoS attack could be. The size and sophistication of the Mirai network was unprecedented as was the scale of the attacks and their focus.

Video: What is Mirai and How do You Protect Yourself Against it?

4. The Mirai Dyn DDoS Attack in 2016

Before we discuss the third notable Mirai botnet DDoS attack of 2016, there’s one related event that should be mentioned. On September 30, someone claiming to be the author of the Mirai software released the source code on various hacker forums and the Mirai DDoS platform has been replicated and mutated scores of times since.

Figure 2. A map of internet outages in Europe and North America caused by the Dyn cyberattack October 2, 2016 / Source: DownDetector (CC BY-SA)

On October 21, 2016, Dyn, a major Domain Name Service (DNS) provider, was assaulted by a one terabit per second traffic flood that then became the new record for a DDoS attack. There’s some evidence that the DDoS attack may have actually achieved a rate of 1.5 terabits per second. The traffic tsunami knocked Dyn’s services offline rendering a number of high-profile websites including GitHub, HBO, Twitter, Reddit, PayPal, Netflix, and Airbnb, inaccessible. Kyle York, Dyn’s chief strategy officer, reported, “We observed 10s of millions of discrete IP addresses associated with the Mirai botnet that were part of the attack.”

Why the Mirai Dyn Attack Matters

Mirai supports complex, multi-vector attacks that make mitigation difficult. Even though the Mirai botnet was responsible for the biggest assaults up to that time, the most notable thing about the 2016 Mirai attacks was the release of the Mirai source code enabling anyone with modest information technology skills to create a botnet and mount a Distributed Denial of Service attack without much effort.

5. The Six Banks DDoS Attack in 2012

On March 12, 2012, six U.S. banks were targeted by a wave of DDoS attacks—Bank of America, JPMorgan Chase, U.S. Bank, Citigroup, Wells Fargo, and PNC Bank. The attacks were carried out by hundreds of hijacked servers from a botnet called Brobot with each attack generating over 60 gigabits of DDoS attack traffic per second.

At the time, these attacks were unique in their persistence. Rather than trying to execute one attack and then backing down, the perpetrators barraged their targets with a multitude of attack methods in order to find one that worked. So, even if a bank was equipped to deal with a few types of DDoS attacks, they were helpless against other types of attack.

Why the Six Banks Attack Matters

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The most remarkable aspect of the bank attacks in 2012 was that the attacks were, allegedly, carried out by the Izz ad-Din al-Qassam Brigades, the military wing of the Palestinian Hamas organization. Moreover, the attacks had a huge impact on the affected banks in terms of revenue, mitigation expenses, customer service issues, and the banks’ branding and image.

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Other Notable Distributed Denial of Service Attacks

6. The GitHub Attack in 2018

On Feb. 28, 2018, GitHub—a platform for software developers—was hit with a DDoS attack that clocked in at 1.35 terabits per second and lasted for roughly 20 minutes. According to GitHub, the traffic was traced back to “over a thousand different autonomous systems (ASNs) across tens of thousands of unique endpoints.”

The following chart shows just how much of a difference there was between normal traffic levels and those of the attack.

Figure 3. Chart of the February 2018 DDoS attack on GitHub. Source: Wired

Even though GitHub was well prepared for a DDoS attack their defenses were overwhelmed—they simply had no way of knowing that an attack of this scale would be launched. As GitHub explained in the company’s incident report: “Over the past year we have deployed additional transit to our facilities. We’ve more than doubled our transit capacity during that time, which has allowed us to withstand certain volumetric attacks without impact to users … Even still, attacks like this sometimes require the help of partners with larger transit networks to provide blocking and filtering.”

Why the GitHub Attack Matters

The GitHub DDoS attack was notable for its scale and the fact that the attack was staged by exploiting a standard command of Memcached, a database caching system for speeding up websites and networks. The Memcached DDoS attack technique is particularly effective as it provides an amplification factor – the ratio of the attacker’s request size to the amount of DDoS attack traffic generated – of up to a staggering 51,200 times.

7. Occupy Central, Hong Kong DDoS Attack in 2014

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The multi-day PopVote DDoS attack was carried out in 2014 and targeted the Hong Kong-based grassroots movement known as Occupy Central, which was campaigning for a more democratic voting system.

In response to their activities, attackers sent large amounts of traffic to three of Occupy Central’s web hosting services, as well as two independent sites, PopVote, an online mock election site, and Apple Daily, a news site, neither of which were owned by Occupy Central but openly supported its cause. Presumably, those responsible were reacting to Occupy Central’s pro-democracy message.

The attack barraged the Occupy Central servers with packets disguised as legitimate traffic and was executed using not one, not two, but five botnets and resulted in peak traffic levels of 500 gigabits per second.

Why the Occupy Central Attack Matters

It was reported that the attackers were probably connected to the Chinese government, there has never been conclusive proof and, perversely, the attack could have been intended to make the Chinese government look bad. The attack may have also provided cover for hackers who managed to extract Occupy Central staff details from a database to mount an extensive subsequent phishing campaign.

8. The CloudFlare DDoS Attack in 2014

In 2014, CloudFlare, a cybersecurity provider and content delivery network, was slammed by a DDoS attack estimated at approximately 400 gigabits per second of traffic. The attack, directed at a single CloudFlare customer and targeted on servers in Europe, was launched using a vulnerability in the Network Time Protocol (NTP) protocol which is used to ensure computer clocks are accurate. Even though the attack was directed at just one of CloudFlare’s customers, it was so powerful it significantly degraded CloudFlare’s own network.

Why the CloudFlare Attack Matters

This attack illustrates a technique where attackers use spoofed source addresses to send fake NTP server responses to the attack target’s servers. This type of attack is known as a “reflection attack,” since the attacker is able to “bounce” bogus requests off of the NTP server while hiding their own address and due to a weakness in the NTP protocol, the amplification factor of the attack can be up to 206 times, making NTP servers a very effective DDoS tool. Shortly after the attack, the U.S. Computer Emergency Readiness team explained NTP amplification attacks are, “especially difficult to block” because “responses are legitimate data coming from valid servers.”

9. The Spamhaus DDoS Attack in 2013

In 2013, a huge DDoS attack was launched against Spamhaus, a nonprofit threat intelligence provider. Although Spamhaus, as an anti-spam organization, was and still is regularly threatened and attacked and had DDoS protection services already in place, this attack—a reflection attack estimated at 300 gigabits of traffic per second—was large enough to knock its website and part of its email services offline.

Why the Spamhaus Attack Matters

The cyberattack was traced to a member of a Dutch company named Cyberbunker, which had apparently targeted Spamhaus after it blacklisted the company for spamming. This illustrates that companies and or rogue employees can mount DDoS attacks with immense brand damaging and serious legal consequences.

DDoS Attack Prevention with A10’s DDoS Protection Solutions

Even though new types of Distributed Denial of Service attacks appear frequently, A10 Thunder® Threat Protection System (TPS) employs advanced defense strategies that protect against all kinds of cyberattacks including new, novel DDoS attacks that could bring down your online and in-house services. Visit A10’s DDoS Protection solution page to learn more.

For additional insight, including the top reflector searches and DDoS research insights performed by attackers, download the complete A10 Networks report, The State of DDoS Weapons.

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