Quick Answer
The correct answer is that the DNS server can be used for denial of service, specifically through a DNS amplification attack exploiting an open recursive resolver. This is the most significant security implication because an attacker can send a small DNS query—often for the ANY record type—with a spoofed source IP address set to the victim’s address, causing the open resolver to return a response that is 50 to 100 times larger, thereby flooding the victim’s network with amplified traffic. On the Certified Ethical Hacker CEH exam, this concept tests your understanding of footprinting and service misconfiguration risks; a common trap is to focus on data exposure rather than the amplification vector. Remember the memory tip: “Small query, big reply—open recursion means DoS is nigh.”
This CEH practice question tests your understanding of footprinting and reconnaissance. 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.
During footprinting, a tester finds that the target's DNS server allows recursive queries from the internet. What is the MOST significant security implication of this finding?
Unauthorized zone transfers are possible
Why wrong: Zone transfer requires AXFR, not recursion.
The DNS server can be used for denial of service (amplification)
Why wrong: Option C is more general; D is specific but correct.
The DNS cache can be poisoned easily
Why wrong: Cache poisoning is separate from recursion.
The DNS server can be used for denial of service
Open recursion enables amplification DDoS.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The DNS server can be used for denial of service
Option D is correct because a DNS server that allows recursive queries from the internet can be exploited in a DNS amplification attack, a type of denial-of-service (DoS) attack. The attacker sends a small query with a spoofed source IP (the victim's IP) to the open recursive resolver, which responds with a much larger response (e.g., using the ANY record type), amplifying traffic up to 50-100 times. This floods the victim's network, making the DNS server an unwitting participant in the attack.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Unauthorized zone transfers are possible
Why it's wrong here
Zone transfer requires AXFR, not recursion.
The DNS server can be used for denial of service (amplification)
Why it's wrong here
Option C is more general; D is specific but correct.
The DNS cache can be poisoned easily
Why it's wrong here
Cache poisoning is separate from recursion.
The DNS server can be used for denial of service
Why this is correct
Open recursion enables amplification DDoS.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse 'recursive queries' with 'zone transfers' or 'cache poisoning,' but the CEH exam specifically tests that open recursive resolvers are most critically used for DNS amplification DoS attacks, not for other DNS misconfigurations.
Detailed technical explanation
In a DNS amplification attack, the attacker sends a small query (e.g., 60 bytes) for the ANY record type to an open recursive resolver, which responds with a large response (e.g., 4000 bytes). The response is sent to the spoofed victim IP, and with many such queries, the victim's bandwidth is saturated. Real-world examples include the 2016 DDoS attack on Dyn DNS, where open resolvers were used to amplify traffic, reaching over 1 Tbps.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CEH exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Footprinting and Reconnaissance — This question tests Footprinting and Reconnaissance — Read the scenario before looking for a memorised answer..
The correct answer is: The DNS server can be used for denial of service — Option D is correct because a DNS server that allows recursive queries from the internet can be exploited in a DNS amplification attack, a type of denial-of-service (DoS) attack. The attacker sends a small query with a spoofed source IP (the victim's IP) to the open recursive resolver, which responds with a much larger response (e.g., using the ANY record type), amplifying traffic up to 50-100 times. This floods the victim's network, making the DNS server an unwitting participant in the attack.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
This CEH practice question is part of Courseiva's free EC-Council 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 CEH exam.
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