Quick Answer
The answer is session hijacking, specifically a TCP session hijacking sequence prediction attack. This is correct because TCP relies on sequence numbers to maintain the order and integrity of packets between a client and server; by intercepting the session and analyzing these numbers, an attacker can predict the next valid sequence number and inject malicious packets, effectively impersonating the legitimate party. On the Certified Ethical Hacker CEH exam, this scenario tests your understanding of network-level session hijacking versus application-level hijacking, and it often appears as a distractor against man-in-the-middle or replay attacks—remember that prediction focuses on the TCP handshake state, not just capturing data. A common trap is confusing this with IP spoofing, but the key difference is the attacker must maintain the correct sequence to stay synchronized. Memory tip: think “SEQ = Session Hijack Enabler for Guessing.”
This CEH practice question tests your understanding of malware, social engineering and network attacks. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An attacker intercepts a TCP session between a client and a server. By analyzing sequence numbers, the attacker successfully predicts the next sequence number and injects malicious packets. Which attack is being performed?
DNS spoofing
Why wrong: DNS spoofing corrupts DNS resolution, not TCP sequence numbers.
ARP poisoning
Why wrong: ARP poisoning redirects traffic, but does not directly involve TCP sequence prediction.
Man-in-the-middle
Why wrong: MITM is a broader positioning; the specific technique described is TCP sequence prediction.
Session hijacking
Session hijacking involves taking over a TCP session by predicting sequence numbers.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Session hijacking
TCP session hijacking relies on predicting or obtaining valid sequence numbers to impersonate one party in a TCP connection.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
DNS spoofing
ARP poisoning
Man-in-the-middle
Why it's wrong here
MITM is a broader positioning; the specific technique described is TCP sequence prediction.
Session hijacking
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CEH NAT questions on configuration and troubleshooting.
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FAQ
Malware, Social Engineering and Network Attacks — This question tests Malware, Social Engineering and Network Attacks — Static NAT maps one inside address to one outside address..
The correct answer is: Session hijacking — TCP session hijacking relies on predicting or obtaining valid sequence numbers to impersonate one party in a TCP connection.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CEH NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An analyst observes the following output from Wireshark: a TCP packet with the SYN flag set, followed by a SYN-ACK, then an ACK, and then a RST. The sequence numbers show a pattern: initial seq=100, ack=300, then seq=300, ack=101. What is the MOST likely interpretation?
hardWhy A: The sequence numbers (100, 300) suggest the attacker correctly guessed the TCP sequence numbers to spoof a connection. The three-way handshake completes (SYN, SYN-ACK, ACK), then the attacker sends a RST to close. This is indicative of TCP sequence prediction attack (session hijacking attempt).
Last reviewed: Jun 21, 2026
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