The answer is DNS poisoning, specifically DNS cache poisoning. This is correct because the burst of unsolicited DNS responses from outside the network is the attacker’s method of injecting forged records into the resolver’s cache, overwriting the legitimate mapping of the internal host name to an unexpected public IP address. Once cached, the poisoned entry redirects users to a lookalike login page, which is the classic outcome of this attack. On the Security+ SY0-701 exam, this scenario tests your understanding of how DNS integrity is compromised at the resolver level, often appearing in questions about man-in-the-middle or redirection attacks. A common trap is confusing this with ARP poisoning, but remember: DNS poisoning corrupts the name-to-IP mapping in the cache, not the MAC-to-IP table. A helpful memory tip is “DNS = Domain Name Spoofing,” where the attacker spoofs the response before the real one arrives.
SY0-701 Threats, Vulnerabilities, and Mitigations Practice Question
This SY0-701 practice question tests your understanding of threats, vulnerabilities, and mitigations. 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.
A resolver log shows multiple clients querying the correct internal host name, but the DNS server starts returning an unexpected public IP address after a burst of unsolicited DNS responses from outside the network. Users are sent to a lookalike login page. What type of attack is most likely occurring?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DNS poisoning
The scenario describes a DNS poisoning (also known as DNS cache poisoning) attack. The burst of unsolicited DNS responses from outside the network is the attacker injecting forged DNS records into the resolver's cache, causing it to map the correct internal host name to an unexpected public IP address. This redirects users to a lookalike login page, which is the classic outcome of DNS poisoning.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
DNS poisoning
Why this is correct
DNS poisoning is the best fit when incorrect DNS records or forged responses cause clients to resolve a legitimate name to a malicious address.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Brute-force authentication
Why it's wrong here
Brute-force attacks guess credentials, but they do not change name resolution results or redirect users through DNS responses.
✗
Port scanning
Why it's wrong here
Port scanning enumerates open services and does not cause clients to be redirected to a counterfeit website.
✗
Packet sniffing
Why it's wrong here
Packet sniffing is passive traffic capture, while this scenario requires active manipulation of DNS resolution.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse DNS poisoning with packet sniffing because both involve network traffic, but only DNS poisoning actively modifies cached resolution data to redirect users.
Trap categories for this question
Scenario analysis trap
Packet sniffing is passive traffic capture, while this scenario requires active manipulation of DNS resolution.
Detailed technical explanation
How to think about this question
DNS poisoning exploits the lack of source port randomization or transaction ID verification in older DNS implementations (RFC 5452). The attacker sends a flood of forged DNS responses with guessed transaction IDs; if one matches the resolver's pending query, the fake record is cached. Modern resolvers use DNSSEC (RFC 4033-4035) and randomized source ports to mitigate this, but legacy systems remain vulnerable.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SY0-701 question in full detail.
Threats, Vulnerabilities, and Mitigations — This question tests Threats, Vulnerabilities, and Mitigations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: DNS poisoning — The scenario describes a DNS poisoning (also known as DNS cache poisoning) attack. The burst of unsolicited DNS responses from outside the network is the attacker injecting forged DNS records into the resolver's cache, causing it to map the correct internal host name to an unexpected public IP address. This redirects users to a lookalike login page, which is the classic outcome of DNS poisoning.
What should I do if I get this SY0-701 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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