Editing Denial-of-service attack (section)

==Attack techniques==

===Attack tools===
In cases such as [[MyDoom]] and [[Slowloris (computer security)|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 (computing)|client program]] to connect to handlers which are compromised systems that issue commands to the [[Zombie computer|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.<ref name="Dittrich" />

In other cases a machine may become part of a DDoS attack with the owner's consent, for example, in [[Operation Payback]] organized by the group [[Anonymous (hacker group)|Anonymous]]. The [[Low Orbit Ion Cannon]] has typically been used in this way. Along with [[High Orbit Ion Cannon]] a wide variety of DDoS tools are available today, including paid and free versions, with different features available. There is an underground market for these in hacker-related forums and IRC channels.

===Application-layer attacks===
Application-layer attacks employ DoS-causing [[exploit (computer security)|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 firewall]]s (WAFs). All attacks belonging to the category of ''timeout exploiting''.<ref>Cambiaso, Enrico; Papaleo, Gianluca; Chiola, Giovanni; Aiello, Maurizio (2015). "Designing and modeling the slow next DoS attack". ''Computational Intelligence in Security for Information Systems Conference (CISIS 2015)''. 249-259. Springer.</ref>

[[Slow DoS attack]]s implement an application-layer attack. Examples of threats are Slowloris, establishing pending connections with the victim, or [[Slowdroid|SlowDroid]], an attack running on mobile devices. Another target of DDoS attacks may be to produce added costs for the application operator, when the latter uses resources based on [[cloud computing]]. In this case, normally application-used resources are tied to a needed quality of service (QoS) level (e.g. responses should be less than 200&nbsp;ms) and this rule is usually linked to automated software (e.g. Amazon CloudWatch<ref>{{cite web|url=http://aws.amazon.com/cloudwatch/|title=Amazon CloudWatch|work=Amazon Web Services, Inc.}}</ref>) to raise more virtual resources from the provider to meet the defined QoS levels for the increased requests. The main incentive behind such attacks may be to drive the application owner to raise the elasticity levels to handle the increased application traffic, to cause financial losses, or force them to become less competitive. A ''banana attack'' is another particular type of DoS. It involves redirecting outgoing messages from the client back onto the client, preventing outside access, as well as flooding the client with the sent packets. A [[LAND]] attack is of this type.

===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.<ref>{{cite book |title=Encyclopaedia Of Information Technology |page=397 |publisher=Atlantic Publishers & Distributors |year=2007 |isbn=978-81-269-0752-6}}</ref><ref>{{cite book|title=Internet and the Law |year=2006 |page=325 |first=Aaron |last=Schwabach |publisher=ABC-CLIO |isbn=978-1-85109-731-9}}</ref> Exposure of degradation-of-service attacks is complicated further by the matter of discerning whether the server is really being attacked or is experiencing higher than normal legitimate traffic loads.<ref>{{cite book|title=Networking and Mobile Computing |first=Xicheng |last=Lu |author2=Wei Zhao |publisher=Birkhäuser |year=2005 |isbn=978-3-540-28102-3 |page=424}}</ref>

===Distributed DoS attack===
If an attacker mounts an attack from a single host, it would be classified as a DoS attack. Any attack against availability would be classed as a denial-of-service attack. On the other hand, if an attacker uses many systems to simultaneously launch attacks against a remote host, this would be classified as a DDoS attack. [[Malware]] can carry DDoS attack mechanisms; one of the better-known examples of this was [[MyDoom]]. Its DoS mechanism was triggered on a specific date and time. This type of DDoS involved hardcoding the target [[IP address]] before releasing the malware and no further interaction was necessary to launch the attack. A system may also be compromised with a [[Trojan horse (computing)|trojan]] containing a [[Zombie computer|zombie agent]]. Attackers can also break into systems using automated tools that exploit flaws in programs that listen for connections from remote hosts. This scenario primarily concerns systems acting as servers on the web. [[Stacheldraht]] is a classic example of a DDoS tool. It uses a layered structure where the attacker uses a [[Client (computing)|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. Each handler can control up to a thousand agents.<ref name="Dittrich">{{cite web |url=http://staff.washington.edu/dittrich/misc/stacheldraht.analysis.txt |title=The "stacheldraht" distributed denial of service attack tool |first=David |last=Dittrich |publisher=University of Washington |date=December 31, 1999 |access-date=2013-12-11 |archive-date=2000-08-16 |archive-url=https://web.archive.org/web/20000816021357/http://staff.washington.edu/dittrich/misc/stacheldraht.analysis.txt |url-status=dead }}</ref> In some cases a machine may become part of a DDoS attack with the owner's consent, for example, in [[Operation Payback]], organized by the group [[Anonymous (hacker group)|Anonymous]]. These attacks can use different types of internet packets such as TCP, UDP, ICMP, etc.

These collections of compromised systems are known as [[botnet]]s. DDoS tools like [[Stacheldraht]] still use classic DoS attack methods centered on [[IP spoofing]] and amplification like [[smurf attack]]s and [[fraggle attack]]s (types of bandwidth consumption attacks). [[SYN flood]]s (a resource starvation attack) may also be used. Newer tools can use DNS servers for DoS purposes. Unlike MyDoom's DDoS mechanism, botnets can be turned against any IP address. [[Script kiddie]]s use them to deny the availability of well known websites to legitimate users.<ref name="SANS">{{cite web|url=http://www.sans.org/resources/idfaq/trinoo.php|title=SANS Institute – Intrusion Detection FAQ: Distributed Denial of Service Attack Tools: n/a|access-date=2008-05-02|publisher=SANS Institute|year=2000|first=Phillip|last=Boyle|archive-url=https://web.archive.org/web/20080515025103/http://www.sans.org/resources/idfaq/trinoo.php|archive-date=2008-05-15|url-status=dead}}</ref> More sophisticated attackers use DDoS tools for the purposes of [[extortion]]{{spaced ndash}}including against their business rivals.<ref>{{cite web|last=Leyden |first=John |url=https://www.theregister.co.uk/2004/09/23/authorize_ddos_attack/ |title=US credit card firm fights DDoS attack |work=The Register |date=2004-09-23 |access-date=2011-12-02}}</ref> It has been reported that there are new attacks from [[internet of things]] (IoT) devices that have been involved in denial of service attacks.<ref>{{cite web|url=http://thehackernews.com/2015/10/cctv-camera-hacking.html|title=Hacking CCTV Cameras to Launch DDoS Attacks|author=Swati Khandelwal|date=23 October 2015|work=The Hacker News}}</ref> In one noted attack that was made peaked at around 20,000 requests per second which came from around 900 CCTV cameras.<ref>{{cite web|url=https://www.incapsula.com/blog/cctv-ddos-botnet-back-yard.html|title=CCTV DDoS Botnet In Our Own Back Yard|first1=Igal|last1=Zeifman|first2=Ofer|last2=Gayer|first3=Or|last3=Wilder|website=incapsula.com|date=21 October 2015}}</ref> UK's [[GCHQ]] has tools built for DDoS, named PREDATORS FACE and ROLLING THUNDER.<ref name="firstlook.org">{{cite web |date=2014-07-15 |author= Glenn Greenwald |url=https://theintercept.com/2014/07/14/manipulating-online-polls-ways-british-spies-seek-control-internet/ |title=HACKING ONLINE POLLS AND OTHER WAYS BRITISH SPIES SEEK TO CONTROL THE INTERNET |website=The Intercept_ |access-date=2015-12-25}}</ref>

Simple attacks such as SYN floods may appear with a wide range of source IP addresses, giving the appearance of a distributed DoS. These flood attacks do not require completion of the TCP [[three-way handshake]] and attempt to exhaust the destination SYN queue or the server bandwidth. Because the source IP addresses can be trivially spoofed, an attack could come from a limited set of sources, or may even originate from a single host. Stack enhancements such as [[SYN cookies]] may be effective mitigation against SYN queue flooding but do not address bandwidth exhaustion. In 2022, TCP attacks were the leading method in DDoS incidents, accounting for 63% of all DDoS activity. This includes tactics like [[TCP SYN]], TCP ACK, and TCP floods. With TCP being the most widespread networking protocol, its attacks are expected to remain prevalent in the DDoS threat scene.<ref name=":2" />

===DDoS extortion===
In 2015, DDoS botnets such as DD4BC grew in prominence, taking aim at financial institutions.<ref>{{cite news|title=Who's Behind DDoS Attacks and How Can You Protect Your Website?|url=http://blog.cloudbric.com/2015/09/whos-behind-ddos-attacks-and-how-can.html|access-date=15 September 2015|agency=Cloudbric|date=10 September 2015}}</ref> 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]].<ref>{{cite news|last1=Solon|first1=Olivia|title=Cyber-Extortionists Targeting the Financial Sector Are Demanding Bitcoin Ransoms|url=https://www.bloomberg.com/news/articles/2015-09-09/bitcoin-ddos-ransom-demands-raise-dd4bc-profile?mod=djemRiskCompliance|access-date=15 September 2015|agency=Bloomberg|date=9 September 2015}}</ref> 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.<ref>{{cite news|last1=Greenberg|first1=Adam|title=Akamai warns of increased activity from DDoS extortion group|url=http://www.scmagazineuk.com/akamai-warns-of-increased-activity-from-ddos-extortion-group/article/438333/|access-date=15 September 2015|agency=SC Magazine|date=14 September 2015}}</ref>

===HTTP slow POST DoS attack===
First discovered in 2009, the HTTP slow POST attack sends a complete, legitimate [[POST (HTTP)|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 (e.g. 1 byte/110 seconds). 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 victim server are exhausted, making any further connections impossible until all data has been sent. It is notable that unlike many other DDoS or DDoS 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.<ref>{{cite web |url=https://www.owasp.org/images/4/43/Layer_7_DDOS.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.owasp.org/images/4/43/Layer_7_DDOS.pdf |archive-date=2022-10-09 |url-status=live|title=OWASP Plan - Strawman - Layer_7_DDOS.pdf |date=18 March 2014|website= Open Web Application Security Project|access-date=18 March 2014}}</ref> Combined with the fact that the [[Apache HTTP Server]] 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 model|open source]] web application security project, released a tool to test the security of servers against this type of attack.<ref>{{cite web |url=https://www.owasp.org/index.php/OWASP_HTTP_Post_Tool |title=OWASP HTTP Post Tool |archive-url=https://web.archive.org/web/20101221131703/https://www.owasp.org/index.php/OWASP_HTTP_Post_Tool |archive-date=2010-12-21}}</ref>

===Challenge Collapsar (CC) attack===
A Challenge Collapsar (CC) attack is an attack where standard HTTP requests are sent to a targeted web server frequently. The [[Uniform Resource Identifier]]s (URIs) in the requests require complicated time-consuming algorithms or database operations which may exhaust the resources of the targeted web server.<ref>{{cite web|url=https://support.huaweicloud.com/en-us/antiddos_faq/antiddos_01_0020.html|title=What Is a CC Attack?|website=HUAWEI CLOUD-Grow With Intelligence|language=en|access-date=2019-03-05|url-status=live|archive-url=https://web.archive.org/web/20190305080627/https://support.huaweicloud.com/en-us/antiddos_faq/antiddos_01_0020.html|archive-date=2019-03-05}}</ref><ref>{{cite web|url=https://patents.google.com/patent/CN106161451A/en|author=刘鹏|author2=郭洋|title=CC (challenge collapsar) attack defending method, device and system|website=Google Patents|language=en|access-date=2018-03-05|url-status=live|archive-url=https://web.archive.org/web/20190305080850/https://patents.google.com/patent/CN106161451A/en|archive-date=2019-03-05}}</ref><ref>{{cite web|url=https://patents.google.com/patent/CN106330911A/en|author=曾宪力|author2=史伟|author3=关志来|author4=彭国柱|title=CC (Challenge Collapsar) attack protection method and device|website=Google Patents|language=en|access-date=2018-03-05|url-status=live|archive-url=https://web.archive.org/web/20190305081050/https://patents.google.com/patent/CN106330911A/en|archive-date=2019-03-05}}</ref> 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''.<ref>{{cite web|url=http://digi.163.com/14/0724/19/A1UL2O95001618JV.html|title=史上最臭名昭著的黑客工具 CC的前世今生|language=zh-hans|website=NetEase|publisher=驱动中国网(北京)|date=2014-07-24|access-date=2019-03-05|url-status=dead|archive-url=https://web.archive.org/web/20190305080935/http://digi.163.com/14/0724/19/A1UL2O95001618JV.html|archive-date=2019-03-05}}</ref>

===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 [[Internet Protocol|IP]] packets with the source address faked to appear to be the address of the victim.<ref>{{Cite journal |last=Sun |first=Fei Xian |date=2011 |title=Danger Theory Based Risk Evaluation Model for Smurf Attacks |url=https://www.scientific.net/KEM.467-469.515 |journal=Key Engineering Materials |language=en |volume=467-469 |pages=515–521 |doi=10.4028/www.scientific.net/KEM.467-469.515 |s2cid=110045205 |issn=1662-9795}}</ref> 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's computer and can even make it unusable during such an attack.<ref name="ANML-DDoS">{{cite web|url=http://anml.iu.edu/ddos/types.html|title=Types of DDoS Attacks |publisher=Advanced Networking Management Lab (ANML) |work=Distributed Denial of Service Attacks(DDoS) Resources, Pervasive Technology Labs at Indiana University |date=December 3, 2009 |archive-url=https://web.archive.org/web/20100914222536/http://anml.iu.edu/ddos/types.html |archive-date=2010-09-14 |access-date=December 11, 2013 }}</ref>

[[Ping flood]] is based on sending the victim an overwhelming number of [[ping (networking utility)|ping]] packets, usually using the ''ping'' command from [[Unix-like]] hosts.{{Efn|The -t flag on [[Microsoft Windows|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 (computing)|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 (Computer Security)|BlackNurse]] attack is an example of an attack taking advantage of the required Destination Port Unreachable ICMP packets.

===Nuke===
A nuke is an old-fashioned denial-of-service attack against [[computer network]]s consisting of fragmented or otherwise invalid [[Internet Control Message Protocol|ICMP]] packets sent to the target, achieved by using a modified [[ping (networking utility)|ping]] utility to repeatedly send this [[Data corruption|corrupt data]], thus slowing down the affected computer until it comes to a complete stop.<ref name="Nuke">{{Cite web|url=https://security.radware.com/ddos-knowledge-center/ddospedia/nuke/|title=What Is a Nuke? {{!}} Radware — DDoSPedia|website=security.radware.com|access-date=2019-09-16}}</ref> 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 [[Transmission Control Protocol|TCP]] port 139 of the victim's machine, causing it to lock up and display a [[Blue Screen of Death]].<ref name="Nuke" />

===Peer-to-peer attacks===
{{See also|Direct Connect (protocol)#Direct Connect used for DDoS 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++]].{{cn|date=December 2024}}{{ambiguous|date=December 2024}} 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 [[file sharing|peer-to-peer file sharing]] hubs to disconnect from their peer-to-peer network and to connect to the victim's website instead.<ref>{{cite web|url=http://www.prolexic.com/news/20070514-alert.php|title=Prolexic Distributed Denial of Service Attack Alert |access-date=2007-08-22|author=Paul Sop|date=May 2007|work=Prolexic Technologies Inc.|archive-url = https://web.archive.org/web/20070803175513/http://www.prolexic.com/news/20070514-alert.php  |archive-date = 2007-08-03}}</ref><ref>{{cite web|url=http://www.securityfocus.com/news/11466|title=Peer-to-peer networks co-opted for DOS attacks|access-date=2007-08-22|author=Robert Lemos|date=May 2007|publisher=SecurityFocus|archive-date=2015-09-24|archive-url=https://web.archive.org/web/20150924114938/http://www.securityfocus.com/news/11466|url-status=dead}}</ref><ref>{{cite web|url=http://dcpp.wordpress.com/2007/05/22/denying-distributed-attacks/|title=Denying distributed attacks|access-date=2007-08-22|author=Fredrik Ullner|date=May 2007|publisher=DC++: Just These Guys, Ya Know? }}</ref>

===Permanent denial-of-service attacks===
Permanent denial-of-service (PDoS), also known loosely as phlashing,<ref>{{cite news|title=Phlashing attack thrashes embedded systems|first=John|last=Leyden|date=2008-05-21|access-date=2009-03-07|work=The Register|url=https://www.theregister.co.uk/2008/05/21/phlashing/}}</ref> is an attack that damages a system so badly that it requires replacement or reinstallation of hardware.<ref name="TechWeb">{{cite web|url=http://www.darkreading.com/document.asp?doc_id=154270&WT.svl=news1_1|title=Permanent Denial-of-Service Attack Sabotages Hardware|publisher=Dark Reading |date=May 19, 2008 |first=Kelly |last=Jackson Higgins |archive-url=https://web.archive.org/web/20081208002732/http://www.darkreading.com/security/management/showArticle.jhtml?articleID=211201088 |archive-date=December 8, 2008}}</ref> 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 [[Router (computing)|routers]], printers, or other [[networking hardware]]. The attacker uses these [[Vulnerability (computer security)|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.'' The intent is to [[Brick (electronics)|brick]] the device, rendering it unusable for its original purpose until it can be repaired or replaced. The PDoS is a pure hardware-targeted attack that can be much faster and requires fewer resources than using a botnet in a DDoS attack. Because of these features, and the potential and high probability of security exploits on network-enabled embedded devices, 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.<ref>{{cite web|title="BrickerBot" Results In PDoS Attack|url=https://security.radware.com/ddos-threats-attacks/brickerbot-pdos-permanent-denial-of-service/|website=Radware|access-date=January 22, 2019|date=May 4, 2017}}</ref> 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, UK.<ref name="EUSecWest">{{cite web|url=http://eusecwest.com/speakers.html#PhlashDance|archive-url=https://web.archive.org/web/20090201173324/http://eusecwest.com/speakers.html#PhlashDance|archive-date=2009-02-01|title=EUSecWest Applied Security Conference: London, U.K.|publisher=EUSecWest|year=2008}}</ref>

===Reflected 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 [[IP address spoofing|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 '''distributed reflective denial-of-service''' ('''DRDoS''') attack.<ref>{{cite web|url=http://www.internetsociety.org/sites/default/files/01_5.pdf|title=Amplification Hell: Revisiting Network Protocols for DDoS Abuse|first=Christian|last=Rossow|publisher=Internet Society|date=February 2014|access-date=4 February 2016|archive-url=https://web.archive.org/web/20160304015033/http://www.internetsociety.org/sites/default/files/01_5.pdf|archive-date=4 March 2016|url-status=dead}}</ref> [[ICMP echo request]] attacks ([[Smurf attack]]s) can be considered one form of reflected attack, as the flooding hosts 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.

===Amplification===
Amplification attacks are used to magnify the bandwidth that is sent to a victim. Many services can be exploited to act as reflectors, some harder to block than others.<ref>{{cite web |last=Paxson|first=Vern |year=2001|url=http://www.icir.org/vern/papers/reflectors.CCR.01/reflectors.html |title=An Analysis of Using Reflectors for Distributed Denial-of-Service Attacks |publisher=ICIR.org}}</ref> US-CERT have observed that different services may result in different amplification factors, as tabulated below:<ref>{{cite web |date=July 8, 2014 |title=Alert (TA14-017A) UDP-based Amplification Attacks |publisher=US-CERT |url=http://www.us-cert.gov/ncas/alerts/TA14-017A |access-date=2014-07-08}}</ref>

{| class="wikitable"
|+ UDP-based amplification attacks
|-
! Protocol
! Amplification factor
! Notes
|-
| [[Mitel]] MiCollab
| 2,200,000,000<ref>{{cite web| url=https://blog.cloudflare.com/cve-2022-26143-amplification-attack/ |title=CVE-2022-26143: A Zero-Day vulnerability for launching UDP amplification DDoS attacks|website=[[Cloudflare]] Blog|date=2022-03-08|access-date=16 March 2022}}</ref>
|
|-
| [[Memcached]]
| 50,000
| Fixed in version 1.5.6<ref>{{cite web| url=https://github.com/memcached/memcached/wiki/ReleaseNotes156 |title=Memcached 1.5.6 Release Notes|website=[[GitHub]]|date=2018-02-27|access-date=3 March 2018}}</ref>
|-
| [[Network Time Protocol|NTP]]
| 556.9
| Fixed in version 4.2.7p26<ref>{{cite web|url=http://support.ntp.org/bin/view/Main/SecurityNotice#April_2010_DRDoS_Amplification_A|title=DRDoS / Amplification Attack using ntpdc monlist command|publisher=support.ntp.org|date=2010-04-24|access-date=2014-04-13}}</ref>
|-
| [[CHARGEN]]
| 358.8
|
|-
| [[DNS]]
| up to 179<ref>{{Cite book |last=van Rijswijk-Deij|first=Roland |title=Proceedings of the 2014 Conference on Internet Measurement Conference |chapter=DNSSEC and its potential for DDoS attacks: A comprehensive measurement study |year=2014|pages=449–460 |publisher=ACM Press|doi=10.1145/2663716.2663731 |isbn=9781450332132 |s2cid=2094604 |url=https://research.utwente.nl/en/publications/dnssec-and-its-potential-for-ddos-attacks--a-comprehensive-measurement-study(cb44e199-21c2-4486-ba0e-8a27c80b8a4f).html }}</ref>
|
|-
| [[QOTD]]
| 140.3
|
|-
| [[Quake engine#Network play|Quake Network Protocol]]
| 63.9
| Fixed in version 71
|-
| [[BitTorrent]]
| 4.0 - 54.3<ref>{{cite web |last=Adamsky|first=Florian |year=2015|url=https://www.usenix.org/conference/woot15/workshop-program/presentation/p2p-file-sharing-hell-exploiting-bittorrent|title=P2P File-Sharing in Hell: Exploiting BitTorrent Vulnerabilities to Launch Distributed Reflective DoS Attacks}}</ref>
| Fixed in libuTP since 2015
|-
| [[CoAP]]
| 10 - 50
|
|-
| ARMS
| 33.5
|
|-
| [[Simple Service Discovery Protocol|SSDP]]
| 30.8
|
|-
| [[Kad network|Kad]]
| 16.3
|
|-
| [[SNMPv2]]
| 6.3
|
|-
| [[Steam (service)|Steam Protocol]]
| 5.5
|
|-
| [[NetBIOS]]
| 3.8
|
|}

[[Domain Name System|DNS]] amplification attacks involves an attacker sending a DNS name lookup request to one or more public DNS servers, spoofing the source IP address of the targeted victim. The attacker tries to request as much information as possible, thus amplifying the DNS response that is sent to the targeted victim. Since the size of the request is significantly smaller than the response, the attacker is easily able to increase the amount of traffic directed at the target.<ref>{{cite web |year=2006|url=http://www.isotf.org/news/DNS-Amplification-Attacks.pdf |title=DNS Amplification Attacks |publisher=ISOTF |archive-url=https://web.archive.org/web/20101214074629/http://www.isotf.org/news/DNS-Amplification-Attacks.pdf |archive-date=2010-12-14|author1=Vaughn, Randal |author2=Evron, Gadi }}</ref><ref>{{cite web |date=July 8, 2013 |title=Alert (TA13-088A) DNS Amplification Attacks |publisher=US-CERT |url=http://www.us-cert.gov/ncas/alerts/TA13-088A |access-date=2013-07-17}}</ref>

[[Simple Network Management Protocol]] (SNMP) and [[Network Time Protocol]] (NTP) can also be exploited as reflectors in an amplification attack. An example of an amplified DDoS attack through the NTP is through a command called monlist, which sends the details of the last 600 hosts that have requested the time from the NTP server back to the requester. A small request to this time server can be sent using a spoofed source IP address of some victim, which results in a response 556.9 times the size of the request being sent to the victim. This becomes amplified when using botnets that all send requests with the same spoofed IP source, which will result in a massive amount of data being sent back to the victim. It is very difficult to defend against these types of attacks because the response data is coming from legitimate servers. These attack requests are also sent through UDP, which does not require a connection to the server. This means that the source IP is not verified when a request is received by the server. To bring awareness of these vulnerabilities, campaigns have been started that are dedicated to finding amplification vectors which have led to people fixing their resolvers or having the resolvers shut down completely.{{citation needed|date=May 2022}}

===Mirai botnet===
The [[Mirai (malware)|Mirai botnet]] works by using a [[computer 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.<ref name="Mirai">{{Cite journal |title=DDoS in the IoT: Mirai and Other Botnets |journal=Computer |volume=50 |issue=7 |pages=80–84 |language=en-US |doi=10.1109/MC.2017.201|year=2017 |last1=Kolias |first1=Constantinos |last2=Kambourakis |first2=Georgios |last3=Stavrou |first3=Angelos |last4=Voas |first4=Jeffrey |s2cid=35958086 }}</ref> The owner or user will usually have no immediate indication of when the device becomes infected. The IoT device itself is not the direct target of the attack, it is used as a part of a larger attack.<ref name="Kuzmanovic 75–86">{{Cite book|last1=Kuzmanovic|first1=Aleksandar|last2=Knightly|first2=Edward W.|title=Proceedings of the 2003 conference on Applications, technologies, architectures, and protocols for computer communications |chapter=Low-rate TCP-targeted denial of service attacks: The shrew vs. The mice and elephants |date=2003-08-25|publisher=ACM|pages=75–86|doi=10.1145/863955.863966|isbn=978-1581137354|citeseerx=10.1.1.307.4107|s2cid=173992197 }}</ref> Once the hacker has enslaved the desired number of devices, they instruct the devices to try to contact an ISP. In October 2016, a Mirai botnet [[DDoS attacks on Dyn|attacked Dyn]] which is the ISP for sites such as [[Twitter]], [[Netflix]], etc.<ref name="Mirai"/> As soon as this occurred, these websites were all unreachable for several hours.

===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.<ref>{{Cite web|url=https://sourceforge.net/projects/r-u-dead-yet/|title = R-u-dead-yet| date=8 September 2016 }}{{primary source inline|date=March 2023}}</ref>

===SACK Panic===
Manipulating [[maximum segment size]] and [[selective acknowledgement]] (SACK) may be used by a remote peer to cause a denial of service by an [[integer overflow]] in the Linux kernel, potentially causing a [[kernel panic]].<ref name = "SACKPanic, Ubuntu wiki, 2019">{{ cite web | url = https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/SACKPanic | title = SACK Panic and Other TCP Denial of Service Issues | access-date = 21 June 2019 | date = 17 June 2019 | website = [[Ubuntu]] Wiki | archive-url = https://web.archive.org/web/20190619100453/https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/SACKPanic | archive-date = 19 June 2019 | df = dmy-all }}</ref> Jonathan Looney discovered {{CVE|2019-11477|2019-11478|2019-11479}} on June 17, 2019.<ref name = "CVE-2019-11479" >{{ cite web | url = https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11479 | title = CVE-2019-11479 | access-date = 21 June 2019 | website = [[Common Vulnerabilities and Exposures|CVE]] | archive-url = https://web.archive.org/web/20190621224631/https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11479 | archive-date = 21 June 2019 | df = dmy-all }}</ref>

===Shrew attack===
The shrew attack is a denial-of-service attack on the [[Transmission Control Protocol]] where the attacker employs [[man-in-the-middle attack|man-in-the-middle techniques]]. It exploits a weakness in TCP's re-transmission timeout mechanism, using short synchronized bursts of traffic to disrupt TCP connections on the same link.<ref>{{Cite book | last1 = Yu Chen | last2 = Kai Hwang | last3 = Yu-Kwong Kwok | doi = 10.1109/LCN.2005.70 | chapter = Filtering of shrew DDoS attacks in frequency domain | title = The IEEE Conference on Local Computer Networks 30th Anniversary (LCN'05)l | pages = 8 pp | year = 2005 | hdl = 10722/45910 | isbn = 978-0-7695-2421-4 | s2cid = 406686 }}</ref>

===Slow read attack===
A slow read attack sends legitimate application layer requests, but reads responses very slowly, keeping connections open longer hoping to exhaust the server's connection pool. The slow read 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.<ref>{{cite web |url=https://www.netscout.com/what-is-ddos/slow-read-attacks |title=What is a Slow Read DDoS Attack? |publisher=[[NetScout Systems]]}}</ref>

===Sophisticated low-bandwidth Distributed Denial-of-Service Attack===
A sophisticated low-bandwidth DDoS attack is a form of DoS that uses less traffic and increases its 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.<ref name="Ben-Porat 1031–1043">{{Cite journal|title = Vulnerability of Network Mechanisms to Sophisticated DDoS Attacks|journal = IEEE Transactions on Computers|date = 2013-05-01|issn = 0018-9340|pages = 1031–1043|volume = 62|issue = 5|doi = 10.1109/TC.2012.49|first1 = U.|last1 = Ben-Porat|first2 = A.|last2 = Bremler-Barr|first3 = H.|last3 = Levy|s2cid = 26395831}}</ref> 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.<ref name="Ben-Porat 1031–1043"/><ref>{{cite web|url=https://sourceforge.net/projects/slow-http-test/|title=Slow HTTP Test|author=orbitalsatelite|work=SourceForge|date=8 September 2016 }}</ref>

===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 is handled like a connection request, causing the server to spawn a [[half-open connection]], send back a TCP/SYN-ACK packet, and wait for a packet in response from the sender address. However, because the sender's address is forged, the response never comes. These half-open connections exhaust the available connections the server can make, keeping it from responding to legitimate requests until after the attack ends.{{ref RFC|4987}}

===Teardrop attacks===
{{see also|IP fragmentation attack}}

A '''teardrop attack''' involves sending [[Mangled packet|mangled]] [[IP fragment]]s with overlapping, oversized payloads to the target machine. This can crash various operating systems because of a bug in their [[TCP/IP]] [[IPv4#Fragmentation and reassembly|fragmentation re-assembly]] code.<ref name="CERT-1">{{cite web |year=1998 |title=CERT Advisory CA-1997-28 IP Denial-of-Service Attacks |url=https://vuls.cert.org/confluence/display/historical/CERT+Advisory+CA-1997-28+IP+Denial-of-Service+Attacks |access-date=July 18, 2014 |publisher=CERT}}</ref> [[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.{{efn|Although in September 2009, a vulnerability in [[Windows Vista]] was referred to as a ''teardrop attack'', this targeted [[Server Message Block|SMB2]] which is a higher layer than the TCP packets that teardrop used).<ref>{{cite news|url=http://www.zdnet.com/blog/security/windows-7-vista-exposed-to-teardrop-attack/4222 |archive-url=https://web.archive.org/web/20101106101436/http://www.zdnet.com/blog/security/windows-7-vista-exposed-to-teardrop-attack/4222 |url-status=dead |archive-date=6 November 2010 |title=Windows 7, Vista exposed to 'teardrop attack' |work=ZDNet |date=September 8, 2009 |access-date=2013-12-11}}</ref><ref>{{cite web|url=http://www.microsoft.com/technet/security/advisory/975497.mspx |title=Microsoft Security Advisory (975497): Vulnerabilities in SMB Could Allow Remote Code Execution |publisher=Microsoft.com |date=September 8, 2009 |access-date=2011-12-02}}</ref>}} 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.<ref>{{Citation |last=Bhardwaj |first=Akashdeep |title=Solutions for DDoS Attacks on Cloud Environment |date=2023-06-12 |work=New Age Cyber Threat Mitigation for Cloud Computing Networks |pages=42–55 |url=http://dx.doi.org/10.2174/9789815136111123010006 |access-date=2024-02-09 |publisher=BENTHAM SCIENCE PUBLISHERS |doi=10.2174/9789815136111123010006 |isbn=978-981-5136-11-1}}</ref>

===Telephony denial-of-service===
[[Voice over IP]] has made abusive origination of large numbers of [[telephone]] voice calls inexpensive and easily automated while permitting call origins to be misrepresented through [[caller ID spoofing]]. According to the US [[Federal Bureau of Investigation]], telephony denial-of-service (TDoS) has appeared as part of various fraudulent schemes:
* A scammer contacts the victim's banker or broker, impersonating the victim to request a funds transfer. The banker's attempt to contact the victim for verification of the transfer fails as the victim's telephone lines are being flooded with bogus calls, rendering the victim unreachable.<ref>{{cite web|url=https://www.fbi.gov/newark/press-releases/2010/nk051110.htm |title=FBI — Phony Phone Calls Distract Consumers from Genuine Theft |publisher=FBI.gov |date=2010-05-11 |access-date=2013-09-10}}</ref>
* A scammer contacts consumers with a bogus claim to collect an outstanding [[payday loan]] for thousands of dollars. When the consumer objects, the scammer retaliates by flooding the victim's employer with automated calls. In some cases, the displayed caller ID is spoofed to impersonate police or law enforcement agencies.<ref>{{cite web|url=http://www.ic3.gov/media/2013/130107.aspx |title= Internet Crime Complaint Center's (IC3) Scam Alerts January 7, 2013 |work=IC3.gov |date=2013-01-07 |access-date=2013-09-10}}</ref>
* [[Swatting]]: A scammer contacts consumers with a bogus debt collection demand and threatens to send police; when the victim balks, the scammer floods local police numbers with calls on which caller ID is spoofed to display the victim's number. Police soon arrive at the victim's residence attempting to find the origin of the calls.

TDoS can exist even without [[Internet telephony]]. In the [[2002 New Hampshire Senate election phone jamming scandal]], [[telemarketing|telemarketers]] were used to flood political opponents with spurious calls to jam phone banks on election day. Widespread publication of a number can also flood it with enough calls to render it unusable, as happened by accident in 1981 with multiple +1-[[area code]]-867-5309 subscribers inundated by hundreds of calls daily in response to the song "[[867-5309/Jenny]]". TDoS differs from other [[telephone harassment]] (such as [[prank call]]s and [[obscene phone call]]s) by the number of calls originated. By occupying lines continuously with repeated automated calls, the victim is prevented from making or receiving both routine and emergency telephone calls. Related exploits include SMS flooding attacks and [[black fax]] or continuous fax transmission by using a loop of paper at the sender.

===TTL expiry attack===
It takes more router resources to drop a packet with a [[Time to live#IP packets|TTL]] value of 1 or less than it does to forward a packet with a higher TTL value. When a packet is dropped due to TTL expiry, the router CPU must generate and send an [[Internet Control Message Protocol#Time exceeded|ICMP time exceeded]] response. Generating many of these responses can overload the router's CPU.<ref>{{cite web |title=TTL Expiry Attack Identification and Mitigation |url=https://www.cisco.com/c/en/us/about/security-center/ttl-expiry-attack.html |publisher=[[Cisco Systems]] |access-date=2019-05-24}}</ref>

===UPnP attack===
A UPnP attack uses an existing vulnerability in [[Universal Plug and Play]] (UPnP) protocol to get past network security 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 that forwards requests from one outer source to another. 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.<ref>{{Cite news|url=https://www.darkreading.com/new-ddos-attack-method-leverages-upnp/d/d-id/1331799|title=New DDoS Attack Method Leverages UPnP|work=Dark Reading|access-date=2018-05-29|language=en}}</ref><ref>{{Cite news|url=https://www.imperva.com/blog/archive/new-ddos-attack-method-demands-a-fresh-approach-to-amplification-assault-mitigation/|title=New DDoS Attack Method Demands a Fresh Approach to Amplification Assault Mitigation – Blog {{!}} Imperva|date=2018-05-14|work=Blog {{!}} Imperva|access-date=2018-05-29|language=en-US}}</ref>

===SSDP reflection attack===
In 2014, it was discovered that [[Simple Service Discovery Protocol]] (SSDP) was being used in [[DDoS]] attacks known as an [[Simple Service Discovery Protocol#DDoS attack|SSDP reflection attac''k'']] ''with amplification''. Many devices, including some residential routers, have a vulnerability in the UPnP software that allows an attacker to get replies from [[List of TCP and UDP port numbers|UDP port 1900]] to a destination address of their choice. With a [[botnet]] of thousands of devices, the attackers can generate sufficient packet rates and occupy bandwidth to saturate links, causing the denial of services.<ref>{{Cite web|url=https://www.cisecurity.org/ms-isac/|title=Multi-State Information Sharing and Analysis Center|website=CIS}}</ref><ref>{{cite web|url=https://www.us-cert.gov/ncas/alerts/TA14-017A|title=UDP-Based Amplification Attacks|date=18 December 2019 }}</ref><ref name="Cloudflare Blog 2017">{{cite web |last=Majkowski |first=Marek |url=https://blog.cloudflare.com/ssdp-100gbps/ |title=Stupidly Simple DDoS Protocol (SSDP) generates 100 Gbps DDoS |date=2017-06-28 |work=The Cloudflare Blog |access-date=2024-11-20}}</ref> Because of this weakness, the network company [[Cloudflare]] has described SSDP as the "Stupidly Simple DDoS Protocol".<ref name="Cloudflare Blog 2017"/><!--"Stupidly Simple DDoS Protocol" is in the article title only, good general description of the vulnerability though-->

===ARP spoofing===
[[ARP spoofing]] is a common DoS attack that involves a vulnerability in the ARP protocol that allows an attacker to associate their [[MAC address]] to the IP address of another computer or [[Gateway (telecommunications)|gateway]], causing traffic intended for the original authentic IP to be re-routed to that of the attacker, causing a denial of service.