Which Attack Exploits The Three Way Handshake

312-50 refers to the EC-Council Certified Ethical Hacker (CEH) exam, which tests the skills required for ethical hacking and network security. It is designed for individuals pursuing a career in cybersecurity, focusing on penetration testing, network security, and identifying vulnerabilities in systems. The exam is popular among IT professionals who aim to become certified ethical hackers, helping organizations safeguard their digital infrastructure from cyber threats.

Tech Professionals

01 May 2025

ECCouncil

Which Attack Exploits The Three Way Handshake

Certified Ethical Hacker Exam (312-50): Understanding TCP Three-Way Handshake and Protecting Against Attacks

The Certified Ethical Hacker (CEH) exam, also known as the 312-50 exam, is a critical certification for cybersecurity professionals seeking to validate their skills in ethical hacking and penetration testing. The CEH credential equips individuals with the knowledge required to identify and address vulnerabilities in a network. One of the key areas covered in the exam is understanding the Transmission Control Protocol (TCP) and its vulnerabilities. Among the most important concepts within TCP is the three-way handshake, which forms the foundation of most networking protocols. This article provides an overview of the TCP three-way handshake, attacks exploiting this process, and methods for detecting and preventing such attacks.

Brief Explanation of the 312-50 Exam (Certified Ethical Hacker Exam)

The CEH exam (312-50) is designed for IT professionals and cybersecurity practitioners who wish to become proficient in ethical hacking. This certification test covers a wide range of topics that are essential for penetration testing, vulnerability assessment, and secure network administration. Ethical hackers use this knowledge to help organizations strengthen their cybersecurity defenses by identifying and fixing potential weaknesses before malicious hackers can exploit them.

The CEH exam tests candidates on various areas, including network security, web application security, cryptography, and ethical hacking methodologies. One crucial aspect of the exam is the understanding of the fundamental concepts of network communication and security protocols. The TCP/IP protocol suite, which is the backbone of most internet communications, plays a central role in this area. Among the key elements of TCP/IP communication is the three-way handshake, which establishes a connection between two devices over a network.

Overview of TCP Three-Way Handshake

The TCP three-way handshake is the process used to establish a reliable connection between a client and a server. It ensures that both sides are ready to communicate and agree on the parameters of the connection. Understanding this process is essential for ethical hackers, as it provides insight into how network connections are initiated and where vulnerabilities may exist.

The three-way handshake involves three distinct steps, each of which is crucial for creating a secure and reliable communication channel:

SYN (Synchronize) Packet: The first step in the handshake begins when the client (the device requesting the connection) sends a SYN (synchronize) packet to the server. This packet is used to request the establishment of a new connection. The SYN packet contains the client’s initial sequence number, which helps both devices maintain the correct order of data packets during communication.
SYN-ACK (Synchronize-Acknowledge) Packet: The server, upon receiving the SYN packet, responds by sending a SYN-ACK (synchronize-acknowledge) packet back to the client. This response serves two purposes: it acknowledges the receipt of the client’s SYN packet and confirms the server's willingness to establish the connection. The SYN-ACK packet also contains the server's own initial sequence number.
ACK (Acknowledge) Packet: The final step occurs when the client responds with an ACK (acknowledge) packet to the server. This packet indicates that the client has received the server’s SYN-ACK packet and is ready to start the communication. At this point, the connection is fully established, and both devices can begin transmitting data securely.

This three-step process ensures that both the client and the server are synchronized and ready to exchange data. It also prevents issues such as data loss or packet duplication, as the sequence numbers help maintain the integrity of the communication.

While the TCP three-way handshake is fundamental to establishing reliable connections, it is not without its vulnerabilities. Ethical hackers must be familiar with potential attacks on the handshake process and how to mitigate them.

Attack Exploiting the Three-Way Handshake

The TCP three-way handshake, while essential for reliable communication, also presents opportunities for attackers to exploit weaknesses in the process. Several types of attacks target the handshake, with the most common being TCP SYN flooding and man-in-the-middle attacks.

1. TCP SYN Flood Attack

A TCP SYN flood is a denial-of-service (DoS) attack that targets the TCP handshake by overwhelming a server with a large number of SYN requests. In a typical three-way handshake, the client sends a SYN packet, waits for the SYN-ACK response from the server, and then sends an ACK packet. However, during a SYN flood attack, the attacker sends numerous SYN requests to the server without completing the handshake by sending the ACK packet. This leaves the server with many half-open connections, consuming its resources and eventually causing it to become unresponsive.

In a SYN flood attack, the attacker exploits the fact that the server will allocate resources for each incoming SYN request. By sending a massive number of SYN packets, the attacker can overwhelm the server’s available resources, making it unable to process legitimate connections. As a result, users may experience service outages or degraded performance.

2. Man-in-the-Middle (MITM) Attack

Another attack that can target the TCP three-way handshake is a man-in-the-middle (MITM) attack. In this type of attack, the attacker intercepts and potentially alters the communication between the client and the server during the handshake process. The attacker may inject malicious packets into the connection, enabling them to eavesdrop on the data being transmitted or even manipulate the communication to execute malicious actions.

In a MITM attack on the three-way handshake, the attacker typically positions themselves between the client and the server. When the client sends a SYN packet to the server, the attacker intercepts it and responds with a SYN-ACK packet of their own. The attacker then waits for the client’s ACK packet and, instead of forwarding it to the server, acknowledges it themselves. This allows the attacker to control the session, potentially gaining access to sensitive information or injecting harmful commands into the communication.

Detection and Prevention of Attacks on the Three-Way Handshake

Since attacks targeting the TCP three-way handshake can severely disrupt network operations, it is essential for ethical hackers to know how to detect and prevent these attacks. Various techniques can be employed to mitigate the risk of SYN floods and man-in-the-middle attacks, ensuring the security and reliability of network connections.

1. Detection and Prevention of SYN Flood Attacks

To detect SYN flood attacks, network administrators can monitor the number of incoming SYN packets. Anomalies in the number of SYN packets or a large number of half-open connections can signal a potential SYN flood attack. There are several techniques that can be employed to defend against such attacks:

SYN Cookies: This technique involves sending a special value (cookie) in the SYN-ACK response to the client, which is difficult for attackers to predict. If the client responds with a valid ACK packet containing the cookie, the server can establish the connection. This prevents the server from allocating resources until the handshake is fully completed.
Rate Limiting: By limiting the number of incoming SYN packets per second from a single source, administrators can slow down or block SYN flood attacks. This can be done using firewall rules or intrusion detection systems (IDS).
Firewall and Intrusion Detection Systems (IDS): Firewalls and IDS can be configured to detect and block SYN flood traffic. These systems can identify unusual traffic patterns and automatically block or rate-limit malicious packets before they reach the server.
Load Balancers: Load balancers can distribute incoming SYN requests across multiple servers, preventing any single server from being overwhelmed. By balancing the load, the risk of a SYN flood attack impacting the entire network is reduced.

2. Detection and Prevention of Man-in-the-Middle (MITM) Attacks

To detect MITM attacks, ethical hackers can use a combination of network monitoring tools and encryption techniques. Key strategies include:

Encryption (SSL/TLS): The most effective way to prevent MITM attacks is to use strong encryption protocols such as SSL/TLS to secure communications. By encrypting the data between the client and the server, any intercepted traffic becomes unreadable to the attacker.
Public Key Infrastructure (PKI): PKI ensures that the parties involved in a connection are who they claim to be. By using digital certificates and asymmetric encryption, PKI can prevent attackers from impersonating legitimate servers or clients during the handshake process.
DNSSEC: DNS Security Extensions (DNSSEC) protect the integrity of DNS queries and responses. By verifying the authenticity of DNS records, DNSSEC reduces the risk of attackers hijacking the connection and performing MITM attacks.
Multi-Factor Authentication: Implementing multi-factor authentication (MFA) further secures the connection, making it more difficult for attackers to gain unauthorized access even if they manage to intercept traffic during the handshake process.
Network Monitoring Tools: Network monitoring tools such as Wireshark can be used to capture and analyze traffic, helping to detect MITM activities. If there is suspicious activity, it may indicate the presence of a MITM attack.

Conclusion

The TCP three-way handshake is a vital component of network communication that ensures reliable and secure connections between devices. Understanding the mechanics of the handshake, as well as the types of attacks that can exploit its vulnerabilities, is essential for ethical hackers. The 312-50 exam (Certified Ethical Hacker Exam) equips professionals with the knowledge and skills needed to assess and secure networks against such threats.