Denial of Service (DoS) and Distributed Denial of Service (DDoS)

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Overview:

Denial of Service (DoS) and Distributed Denial of Service (DDoS) attacks are cyberattacks designed to disrupt or prevent legitimate access to a system, network, or service. DoS attacks overwhelm the target with excessive traffic or requests, causing it to become slow, unresponsive, or completely unavailable. DDoS attacks are a more advanced form, where the malicious traffic originates from multiple sources, making them significantly harder to mitigate and detect.

The primary goal of both DoS and DDoS attacks is to exhaust the resources of a target, such as bandwidth, CPU, and memory, leading to downtime or degraded performance. DDoS attacks are especially dangerous because they can involve large botnets — networks of compromised devices controlled by attackers. These attacks can have devastating consequences for businesses, from financial losses to damaged reputations.

Types of DoS and DDoS Attacks:

DoS Attack: In a basic DoS attack, a single source sends a large volume of requests or traffic to overwhelm the target's resources, making the system or service unavailable to legitimate users. The attacker typically floods the network, server, or application with excessive data or requests that it cannot process. Once the system's limits are reached, it either crashes or experiences severe performance degradation.
DDoS Attack: Unlike a DoS attack, a DDoS attack uses multiple sources (often thousands or millions) to flood the target with traffic. These sources may include infected computers, IoT devices, or servers that form a botnet. The distributed nature of the attack makes it more difficult to mitigate since the traffic is coming from a wide range of IP addresses.
UDP Flood: This attack targets a system by sending a large number of UDP packets to random ports on the target server. Because UDP is a connectionless protocol, the server spends resources trying to respond to these invalid requests, eventually becoming overwhelmed. This type of attack can quickly saturate the network, consuming both bandwidth and processing power.
SYN Flood: A SYN flood exploits the TCP handshake process by sending numerous "SYN" requests to a target system without completing the handshake. The server responds to each SYN request with a "SYN-ACK" message, waiting for the final ACK. However, since the attacker never completes the handshake, the server is left waiting, consuming resources and eventually becoming unable to handle legitimate connections.
HTTP Flood: An HTTP flood is an application layer attack where the attacker sends HTTP requests to a web server to overload it. The goal is not to crash the server directly, but to exhaust its ability to respond to valid user requests, leading to slowdowns or crashes. This type of attack often mimics legitimate web traffic, making it harder to differentiate between malicious and legitimate requests.

How to Perform a DoS or DDoS Attack:

To execute a DoS or DDoS attack, attackers typically start by identifying a vulnerable target, such as a website, server, or network device. In a DoS attack, the attacker may use tools like LOIC (Low Orbit Ion Cannon) or HOIC (High Orbit Ion Cannon), which allow them to send a flood of requests to the target. The attacker would configure the tool to send large volumes of traffic, usually from a single device or IP address, until the target becomes overwhelmed and is unable to process valid requests.

For a DDoS attack, the attacker would typically control a botnet, which is a network of infected devices, often including IoT devices, computers, and servers. Once a botnet is established, the attacker sends commands to all the devices to launch the attack simultaneously, targeting the victim with traffic from multiple sources. This distributed nature makes it harder for defenders to filter out malicious traffic, as the requests come from many different IP addresses and locations.

How to Defend Against DoS and DDoS Attacks:

Traffic Filtering and Rate Limiting: Using Web Application Firewalls (WAFs) and Intrusion Detection Systems (IDS) can help filter out malicious traffic before it reaches the target. Rate limiting can also be implemented to control the number of requests from a single IP address within a specific timeframe, preventing overwhelming traffic.
Use of Content Delivery Networks (CDNs): CDNs can help distribute traffic across a network of servers, alleviating the load on the main server. By caching content closer to the end user, CDNs also improve performance while making it more difficult for DDoS attackers to target a single point of failure.
Deploying Anti-DDoS Protection Services: Many service providers, like Cloudflare or AWS Shield, offer specialized DDoS protection. These services detect and mitigate DDoS attacks in real-time by redirecting traffic through their own infrastructure, filtering out malicious requests before they can impact the target.
Redundancy and Failover Systems: Having backup servers and failover systems can provide fail-safe mechanisms in the event of an attack. By using geographically distributed data centers and load balancing, traffic can be routed around an overwhelmed server, maintaining uptime and service availability.

Real-World Examples:

GitHub DDoS Attack (2018)

In 2018, GitHub was hit by one of the largest DDoS attacks in history, reaching a peak traffic volume of 1.35 terabits per second (Tbps). The attack utilized a technique called "Memcached amplification," where an open source vulnerability was exploited to amplify traffic sent to the target. GitHub's infrastructure, supported by Cloudflare, was able to absorb and mitigate the attack within minutes, minimizing the impact on users.