ISC2 CC Network Security Practice Question
A security analyst detects a large number of half-open TCP connections targeting a web server. This is most likely indicative of what type of attack?
⚠ Common exam trap
A common mix-up: candidates confuse volumetric network attacks (Smurf, DNS amplification) with TCP state exhaustion attacks; candidates may pick Smurf because it also causes many connections, but Smurf uses ICMP, not TCP.
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
✓
SYN flood
A SYN flood attack exploits the TCP three-way handshake by sending numerous SYN packets with spoofed source addresses, causing the server to allocate resources for half-open connections that never complete. The server's connection table fills up, exhausting resources and preventing legitimate connections. This matches the symptom of many half-open TCP connections observed by the analyst.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Smurf attack
Why it's wrong here
Smurf floods a victim with ICMP echo replies via a spoofed broadcast address, producing no TCP handshakes at all. It is tempting because it is a volumetric denial-of-service attack, which would be the answer if the traffic were ICMP rather than half-open TCP connections.
- ✓
SYN flood
Why this is correct
Half-open connections arise when a host receives SYN packets but never completes the three-way handshake, exhausting the backlog queue. A SYN flood deliberately sends spoofed SYNs at volume, matching the observed pattern and denying legitimate clients access to the web server.
- ✗
ARP spoofing
Why it's wrong here
ARP spoofing poisons the IP-to-MAC mapping cache to intercept or redirect local traffic; it does not generate half-open TCP connections on a server. It is tempting as a man-in-the-middle technique, and would be correct if the symptom were duplicated MAC addresses or redirected gateway traffic.
- ✗
DNS amplification
Why it's wrong here
DNS amplification floods a target with large DNS responses sent to a spoofed source address, using UDP port 53 rather than TCP handshakes. It is tempting as a common reflection denial-of-service, and would be correct if the traffic were oversized DNS replies.
Visual reference
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Related to this question
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.
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.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
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