Distributed denial-of-service (DDoS) attacks have become a major threat in the cybersecurity landscape. In a DDoS attack, hackers use botnets – networks of compromised devices – to overwhelm a target with traffic and render its services unavailable. DDoS attacks can be complex to execute but can have devastating impacts on businesses, websites, and networks. Understanding how hackers perform these attacks can help organizations better defend themselves.
What is a DDoS attack?
A distributed denial-of-service (DDoS) attack is a cyberattack in which a perpetrator uses multiple compromised devices to flood a target with traffic. This overwhelms the target’s resources and renders it inaccessible to legitimate users. The ‘distributed’ aspect refers to the fact that the incoming traffic comes from many different sources that are distributed globally.
The purpose of a DDoS attack is to disrupt normal traffic and make a website or other online service unavailable. DDoS attacks achieve this by exhausting the target’s bandwidth, overloading its servers, and occupying resources needed to maintain connectivity.
Some key characteristics of DDoS attacks include:
- Use of botnets – large numbers of compromised devices controlled by the attacker
- Flood of requests to overwhelm the target’s capacity
- Multiple attack vectors – using different traffic types and protocols
- Difficult to block due to distributed nature
- Goal of disrupting availability and accessibility of the target
Common DDoS attack vectors
DDoS attacks typically rely on multiple attack vectors to overwhelm the target. Common attack vectors include:
Volume-based attacks
These attacks aim to saturate the bandwidth of the target using massive amounts of bogus traffic. Some examples include:
- UDP floods – sending high volumes of UDP packets to random ports
- ICMP floods – massive streams of ICMP echo requests (pings)
- SYN floods – incomplete connection requests that overwhelm TCP resources
Protocol attacks
These attacks exploit weaknesses in protocols like TCP and HTTP. Examples include:
- ACK floods – targeting packet acknowledgements
- Fragmentation attacks – sending fragmented packets to overwhelm servers
- Slowloris – opening many connections with minimal traffic
Application layer attacks
These target websites and web-based applications directly. Common examples:
- HTTP floods – bots repeatedly sending HTTP requests
- GET/POST floods – targeting site content or functionality
- DNS query floods – overwhelming DNS servers with requests
Attackers often use a combination of these methods to maximize the impact on the victim. The various traffic streams make DDoS mitigation challenging.
Botnets and their role
Central to most DDoS attacks is a botnet – a network of compromised internet-connected devices that attackers can remotely control and coordinate. Botnets enable attackers to launch large-scale attacks from distributed locations, making them difficult to block.
Botnets are built up over time as attackers infect vulnerable devices and add them to their pool of bots. Common botnet devices include:
- Home/office computers
- Servers
- Smartphones/tablets
- IoT/smart devices
- Routers
Bots are infected with malware that allows the attacker remote access and control. The malware also hides the infection and prevents the device owner from detecting its presence. Attackers can manage botnets using command and control (C&C) software.
When launching a DDoS attack, the attacker sends instructions to the bots telling them when and who to attack. Thousands of bots attacking simultaneously can generate huge attacks that exceed 100 gigabits per second (Gbps).
Botnet resources
Botnets essentially provide cybercriminals with on-demand computing resources to conduct attacks. Key resources offered by botnets:
- Bandwidth – The combined bandwidth across thousands of bots allows for powerful volumetric floods that can saturate a target’s connectivity.
- IPs – A diverse pool of bot IP addresses makes blocking difficult since IPs appear legitimate.
- Geography – Global dispersal across bots enables attacks from anywhere against any target.
- Anonymity – Attack traffic originates from bots rather than the attacker, hiding their identity.
Larger botnets with more devices offer greater attack power. Botnets with over 100,000 devices are common, but some have exceeded 1 million bots.
Stages of a DDoS attack
Launching a large-scale distributed denial-of-service attack involves multiple steps:
1. Building the botnet
The attacker first needs to build up a botnet of compromised devices. This is done by:
- Scanning for vulnerable devices facing the internet
- Exploiting unpatched bugs/weak passwords to gain access
- Installing malware on devices to infect them with bots
- Adding bots to the attacker’s botnet army
Building a large botnet can take considerable time and effort. But once formed, the botnet can be leveraged repeatedly for attacks.
2. Command and control
Botnets rely on command and control (C&C) servers/systems to manage the bots and launch attacks. Common C&C methods include:
- IRC channels – bots connect to an IRC server to receive commands
- Web servers – bots periodically check a website for attack instructions
- P2P protocols – a decentralized network is used to communicate with bots
The C&C allows the attacker to update bots, identify targets, and activate DDoS attacks.
3. Reconnaissance
Before attacking, the attacker performs reconnaissance on the target to identify weaknesses. This includes:
- Network and IP address scanning
- Traffic analysis to study patterns
- Vulnerability scanning
- Service identification
The goal is to optimize attack methods for maximum damage. Any vulnerabilities or weak points are identified.
4. Launching the Attack
When ready to attack, the attacker sends instructions to the bots via the C&C system. This triggers the flood of malicious botnet traffic from distributed locations to the target. Typical commands include:
- Date/time to start the attack
- Type and mix of traffic to use
- IP address/domain of the target
- Duration of the attack
Continually changing the attack vectors and traffic mix makes mitigation difficult for the victim.
5. Completion
Once the attack objectives are achieved or a predetermined time passed, the attacker stops the attack and goes dormant. Bots return to normal operation without the device owner realizing.
The attacker can then prepare for the next attack, incorporating any lessons from the previous one to improve. Botnets and attack methods are continuously enhanced.
DDoS attack tools
Launching effective DDoS attacks requires skill and technical know-how. Advanced hackers write their own attack tools, but beginners often use existing DDoS software.
Some common DDoS attack tool examples include:
LOIC
LOIC (Low Orbit Ion Cannon) is a popular free DDoS tool used by hacktivists. It allows launching basic volume-based attacks like UDP and TCP floods.
HOIC
An upgraded version of LOIC, HOIC (High Orbit Ion Cannon) provides greater power through a voluntary botnet component. Users can voluntarily join the HOIC botnet to increase attack strength.
Darkness
A distributed denial of service toolkit that leverages vulnerabilities in SNMP, UDP, and TCP protocols for powerful attacks.
XOIC
XOIC provides a web interface to allow less technical users to configure parameters and initiate a DDoS attack. Pre-defined attack scripts automate the process.
| DDoS Tool | Details |
|---|---|
| LOIC | Free tool for basic volume-based DDoS attacks like UDP and TCP floods |
| HOIC | Enhanced version of LOIC that incorporates voluntary botnets |
| Darkness | Powerful toolkit that exploits vulnerabilities in common protocols |
| XOIC | Web interface for easy configuration and launching of DDoS attacks |
These lower skill tools allow novice hackers to engage in DDoS activity. But for more sophisticated attacks, hackers use custom malware and botnets tailored to specific targets.
DDoS impact and motives
The potency of modern DDoS attacks enables a wide range of damage depending on the attacker’s motivations:
Service disruption
Rendering a website, application, or online platform inaccessible. This can cause major business disruption, revenue loss, and reputational damage.
Extortion
Threatening a large DDoS attack unless the victim pays a ransom. Many organizations end up paying to avoid an attack.
Hacktivism
Using DDoS to take down websites as an act of protest. Groups like Anonymous often organize hacktivist DDoS campaigns.
Cyber warfare
Nation-states deploying DDoS to censor, monitor, and disrupt enemies in times of conflict. DDoS provides an asymmetric cyberwarfare capability.
Other motives include personal grudges, competitive disruption, testing, and simply vandalism. As long as targets rely on internet availability, DDoS provides power to attackers.
DDoS defense strategies
Defending against modern DDoS attacks requires a layered security approach. Key elements include:
Network monitoring
Monitoring network traffic for anomalies, spikes, and known attack signatures can provide early warning of an emerging DDoS event.
Capacity provisioning
Over-provisioning bandwidth and building in redundancy allows absorbing some degree of attack traffic without outage.
Traffic filtering
Identifying and blocking malicious IP addresses and protocols at the network edge can help prevent attack traffic flooding in.
DDoS protection services
Specialized third-party DDoS mitigation services can scrub attack traffic in the cloud before it hits the target.
BOT management
Detecting and removing bot infections within internal networks and devices limits exposure to zombie bots participating in DDoS attacks.
Combining these capabilities provides layered security and greater resilience against DDoS. But as attacks grow smarter, defenses must continuously adapt.
The future of DDoS attacks
DDoS attack severity and sophistication will likely continue advancing, presenting evolving challenges:
- Increasing scale – Botnets with millions of devices will enable Terabit+ attacks
- New vectors – Abusing emerging protocols and IoT growth areas
- Collaboration – Attacker alliances combining resources and expertise
- Cloud abuse – Leveraging cloud hosting and serverless architectures
- Artificial intelligence – Smarter, context-aware attacks tailored to targets
Organizations will need to invest heavily in DDoS defenses and closely monitor the threat landscape. Staff training and incident response planning will also grow in importance. Ultimately, combating DDoS attacks requires proactive preparation and agility in security approaches.
Conclusion
Distributed denial-of-service attacks present a potent threat capable of debilitating websites, networks, infrastructure, and business operations. Attackers use a variety of techniques to build botnets, generate high volumes of malicious traffic, and overwhelm targets.
Defending against DDoS requires a combination of capacity provisioning, traffic monitoring, filtering, and specialist DDoS mitigation services. As attacks grow smarter, using AI and other new tactics, organizations will need to constantly improve their safeguards and employee expertise. Understanding how DDoS attacks work provides the knowledge to implement robust, multilayered protection.
