The answer is querying certificate transparency logs using a site like crt.sh. This technique is best because certificate transparency logs are public, append-only ledgers that record every SSL/TLS certificate issued by a Certificate Authority, including certificates for subdomains. By searching these logs for the target domain, a tester can passively discover all associated subdomains without ever sending a DNS query to the target’s authoritative servers, keeping the reconnaissance fully stealthy and undetectable. On the CompTIA PenTest+ PT0-002 exam, this question tests your understanding of passive reconnaissance methods that avoid direct interaction with the target’s infrastructure. A common trap is confusing passive subdomain discovery with active techniques like DNS brute-forcing or zone transfers, which generate network traffic and risk detection. Remember the memory tip: “CT logs keep the certificate history—query them passively, and you’ll never leave a trace.”
PT0-002 Practice Question: Information Gathering and Vulnerability Scanning
This PT0-002 practice question tests your understanding of information gathering and vulnerability scanning. 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 penetration tester is conducting passive reconnaissance against a target domain. The tester wants to discover all subdomains associated with the domain without making any direct DNS queries to the target's authoritative servers. Which technique is BEST suited for this purpose?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Using the 'nslookup' command to query the domain's DNS server
Why wrong: This is direct query, not passive.
B
Querying certificate transparency logs using a site like crt.sh
Correct. Certificate transparency logs are public and contain all domains/subdomains that have SSL/TLS certificates issued, providing passive subdomain discovery.
C
Performing a DNS zone transfer
Why wrong: Zone transfer is active and often blocked; also requires querying authoritative server.
D
Using the 'whois' lookup to gather domain registration info
Why wrong: whois provides registration details but not subdomains.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Querying certificate transparency logs using a site like crt.sh
Certificate transparency logs, accessible via sites like crt.sh, provide a historical record of all SSL/TLS certificates issued for a domain, including those for subdomains. Querying these logs allows a tester to discover subdomains without making any direct DNS queries to the target's authoritative servers, thus remaining fully passive and avoiding detection.
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.
✗
Using the 'nslookup' command to query the domain's DNS server
Why it's wrong here
This is direct query, not passive.
✓
Querying certificate transparency logs using a site like crt.sh
Why this is correct
Correct. Certificate transparency logs are public and contain all domains/subdomains that have SSL/TLS certificates issued, providing passive subdomain discovery.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Performing a DNS zone transfer
Why it's wrong here
Zone transfer is active and often blocked; also requires querying authoritative server.
✗
Using the 'whois' lookup to gather domain registration info
Why it's wrong here
whois provides registration details but not subdomains.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse passive reconnaissance with techniques that are technically passive from the tester's perspective but still generate network traffic to the target, such as querying public DNS resolvers or using search engines, whereas certificate transparency logs are truly passive as they rely on third-party data repositories.
Detailed technical explanation
How to think about this question
Certificate transparency logs are based on RFC 6962, which mandates that Certificate Authorities (CAs) publicly log every certificate they issue. Tools like crt.sh aggregate these logs, allowing queries by domain name to retrieve all certificates, including those for subdomains, wildcards, and even expired certificates. This technique is particularly valuable because it can reveal subdomains that are not publicly listed in DNS or that are hidden behind private nameservers.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PT0-002 question in full detail.
Information Gathering and Vulnerability Scanning — This question tests Information Gathering and Vulnerability Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Querying certificate transparency logs using a site like crt.sh — Certificate transparency logs, accessible via sites like crt.sh, provide a historical record of all SSL/TLS certificates issued for a domain, including those for subdomains. Querying these logs allows a tester to discover subdomains without making any direct DNS queries to the target's authoritative servers, thus remaining fully passive and avoiding detection.
What should I do if I get this PT0-002 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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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