easyMultiple ChoiceObjective-mapped
ISC2 CC Practice Question: A security analyst notices that an internal web…
A security analyst notices that an internal web server is receiving a high volume of TCP SYN packets from a single external IP address, but the server is not sending SYN-ACK replies. The server's CPU and memory usage are normal. What is the most likely cause?
⚠ Common exam trap
ISC2 often tests the distinction between a SYN flood (which fills the connection queue) and a DDoS (which involves multiple sources), so candidates mistakenly choose D when the key detail is the single external IP address.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The server is under a SYN flood attack, filling the connection queue
A SYN flood attack works by sending a high volume of TCP SYN packets to a server, filling its half-open connection queue (the backlog) and preventing it from completing the three-way handshake. Since the server's CPU and memory are normal, the issue is not resource exhaustion but rather the queue being saturated, causing the server to stop sending SYN-ACK replies to new connection requests.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A firewall rule is blocking inbound SYN-ACK packets
Why it's wrong here
Firewalls typically block inbound SYNs, not SYN-ACKs; the issue is the server not sending SYN-ACKs.
- ✓
The server is under a SYN flood attack, filling the connection queue
Why this is correct
SYN flood attacks fill the server's half-open connection queue, preventing it from sending SYN-ACKs.
- ✗
The server's TCP/IP stack has crashed
Why it's wrong here
A crash would show abnormal CPU/memory usage, which is normal here.
- ✗
The server is experiencing a distributed denial-of-service (DDoS) attack
Why it's wrong here
A DDoS involves multiple sources, but here only one IP is mentioned.
Visual reference
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Related to this question
Learn chapter
Introduction to Security Principles
Key term
TCP
TCP is a connection-oriented transport layer protocol that ensures reliable, ordered, and error-checked delivery of data between applications over IP networks.
Key term
Denial-of-service
A Denial-of-service (DoS) attack is an attempt to make a computer, network, or online service unavailable to its intended users by overwhelming it with fake traffic or requests.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CC practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CC exam.