Which Attack Exploits The Three-Way Handshake?

The attack that exploits the three-way handshake is called a "SYN Flood" attack. It takes advantage of the initial handshake in TCP connections, overwhelming the target system with fake requests. To learn more about cybersecurity and prevent such attacks, visit Study4Pass for helpful study materials and exam dumps.

Tech Professionals

17 April 2025

CompTIA

Which Attack Exploits The Three-Way Handshake?

Introduction

The three-way handshake is a fundamental process in TCP (Transmission Control Protocol) that establishes a reliable connection between two devices. However, cyber attackers often exploit this mechanism to launch devastating attacks. One such attack is the SYN flood attack, a type of Denial-of-Service (DoS) attack.

For aspiring cybersecurity professionals preparing for the CompTIA Security+ (SY0-701) exam, understanding these attacks is crucial. This article explores how the three-way handshake works, the attacks that exploit it, mitigation techniques, and how Study4Pass can help you ace your certification exam.

Understanding the Three-Way Handshake

Before diving into the attack, let's first understand the three-way handshake process in TCP:

SYN (Synchronize): The client sends a SYN packet to the server to initiate a connection.
SYN-ACK (Synchronize-Acknowledge): The server responds with a SYN-ACK packet, acknowledging the request.
ACK (Acknowledge): The client sends an ACK packet back to the server, completing the connection.

Once this process is complete, data transmission begins.

Why is the Three-Way Handshake Important?

Ensures reliable communication.
Verifies that both devices are ready to transmit data.
Prevents unauthorized or half-open connections.

However, attackers exploit this process to overwhelm servers.

What Attack Exploits the Three-Way Handshake?

The primary attack that exploits the three-way handshake is the SYN flood attack, a type of Denial-of-Service (DoS) or Distributed Denial-of-Service (DDoS) attack.

SYN Flood Attack

In a SYN flood attack, the attacker sends a flood of SYN packets to a target server but never completes the handshake by sending the final ACK. This leaves the server with multiple half-open connections, consuming resources until it becomes unresponsive.

How It Works:

The attacker sends a massive number of SYN requests (often with spoofed IP addresses).
The server allocates resources for each request and sends back SYN-ACK packets.
Since the attacker never responds with an ACK, the server waits, exhausting its connection table.
Legitimate users cannot establish connections, leading to a denial of service.

Other Related Attacks

TCP Reset Attack: An attacker sends fake RST (reset) packets to terminate legitimate connections.
TCP Session Hijacking: Attackers take over an established TCP session by predicting sequence numbers.

How a SYN Flood Attack Works (Step-by-Step)?

Let’s break down a SYN flood attack in detail:

Step 1: Attacker Initiates Multiple SYN Requests

The attacker uses a botnet or spoofed IPs to send thousands of SYN packets to the target server.

Step 2: Server Responds with SYN-ACK

The server reserves resources (memory, CPU) for each SYN request and sends SYN-ACK responses.

Step 3: Attacker Never Completes the Handshake

The attacker ignores the SYN-ACK, leaving connections half-open.
The server waits (default timeout is usually 30-60 seconds).

Step 4: Server Resources Are Exhausted

The server’s connection queue fills up, preventing legitimate users from accessing services.

Step 5: Service Disruption

The target system crashes or becomes extremely slow, causing a denial of service.

Real-World Examples of SYN Flood Attacks

Example 1: 2016 Dyn Cyberattack

One of the largest DDoS attacks in history.
Attackers used a Mirai botnet to flood DNS provider Dyn with SYN requests.
Major websites like Twitter, Netflix, and Reddit went offline.

Example 2: GitHub Attack (2018)

GitHub faced a massive 1.35 Tbps DDoS attack, partially involving SYN floods.
The attack lasted 20 minutes before being mitigated.

These incidents highlight the importance of understanding and defending against SYN flood attacks.

Mitigation Techniques Against SYN Flood Attacks

To protect against SYN flood attacks, organizations use several defense mechanisms:

1. SYN Cookies

The server does not allocate resources until the final ACK is received.
Uses cryptographic hashing to validate connections.

2. Rate Limiting and Filtering

Limits the number of SYN packets per second from a single IP.
Uses firewalls to block suspicious traffic.

3. Increasing Backlog Queue

Expands the server’s capacity to handle half-open connections.

4. Implementing Load Balancers

Distributes traffic across multiple servers to prevent overload.

5. Using Cloud-Based DDoS Protection

Services like Cloudflare, AWS Shield, and Akamai absorb malicious traffic.

CompTIA Security+ (SY0-701) Exam Focus

The SY0-701 exam covers various attack vectors, including TCP-based attacks like SYN floods. Key topics include:

Types of DoS/DDoS attacks
TCP/IP vulnerabilities
Mitigation strategies
Network security controls

Understanding these concepts is crucial for passing the exam and securing real-world networks.

How Study4Pass Helps You Prepare for the SY0-701 Exam?

Preparing for the CompTIA Security+ Exam requires high-quality study materials and practice tests. Study4Pass offers:

Comprehensive Study Guides – Covers all SY0-701 objectives, including TCP attacks.
Realistic Practice Exams – Simulates the actual test environment.
Detailed Explanations – Helps you understand attack mechanisms and defenses.
Up-to-Date Content – Aligned with the latest CompTIA exam trends.

By using Study4Pass, you can confidently master topics like SYN flood attacks and pass your Security+ exam on the first try!

Final Words

The three-way handshake is essential for reliable TCP communication, but attackers exploit it through SYN flood attacks to disrupt services. Understanding these attacks is critical for cybersecurity professionals, especially those preparing for the CompTIA Security+ (SY0-701) exam.

By implementing proper mitigation techniques and leveraging resources like Study4Pass, you can enhance your knowledge and pass your certification with ease.