SY0-701 Threats, Vulnerabilities, and Mitigations Practice Question
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?
⚠ Common exam trap
Test-takers frequently confuse DNS poisoning with packet sniffing because both involve network traffic, but only DNS poisoning actively modifies cached resolution data to redirect users.
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
✓
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.
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 directly corrupts the name resolution process: an attacker either forges a DNS response that arrives before the legitimate answer or tampers with a resolver's cache, causing it to return a fraudulent IP address for a valid domain. This matches the scenario exactly because multiple clients querying the correct record will all receive the malicious answer and be redirected to the counterfeit website, while the resolver log simply shows normal queries.
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Brute-force authentication
Why it's wrong here
Brute-force authentication is a credential-based attack where the attacker repeatedly tries passwords, passphrases, or usernames to log into an account. This process does not alter DNS records, poison caches, or inject forged name-resolution responses, so it cannot cause every client querying a legitimate name to be redirected to a malicious site. The resolver log would remain clean of any DNS corruption, making this option unrelated to the observed symptom.
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Port scanning
Why it's wrong here
Port scanning is a reconnaissance technique used to discover open TCP or UDP services on a host by sending probes to a range of ports. It does not modify DNS resolution behavior, forge responses, or redirect web traffic; an attacker would use a scan merely to identify targets for a separate attack. While a scan might reveal a vulnerable DNS server, the act of scanning itself cannot cause clients to resolve a correct target address to a different, malicious IP.
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Packet sniffing
Why it's wrong here
Packet sniffing is a passive monitoring technique where an attacker captures network traffic to read cleartext data such as credentials or session cookies. Since sniffing only observes and records existing packets, it provides no mechanism to alter DNS query responses or to insert a forged reply that would redirect clients to a counterfeit site. Active manipulation of DNS resolution is required to make the legitimate address resolve incorrectly, and passive capture cannot achieve that effect.
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Related to this question
Learn chapter
Network-Based Attacks
Key term
DNS
DNS is the system that translates human-friendly domain names like example.com into machine-readable IP addresses so computers can find each other on a network.
Key term
IP address
An IP address is a unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SY0-701 practice question is part of Courseiva's free CompTIA 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 SY0-701 exam.