The answer is to examine the SSL certificate Subject Alternative Names (SANs) presented by the ALB. This technique is most effective for internal hostname discovery during an external assessment because SSL/TLS certificates, especially those used by AWS Application Load Balancers, frequently list internal DNS names or private IP ranges in their SAN fields to support multiple secure sites. On the CompTIA PenTest+ PT0-002 exam, this tests your ability to pivot from passive reconnaissance to active enumeration when traditional methods like DNS zone transfers fail—a common trap is overlooking certificate transparency logs or SAN data, assuming only public names are present. Remember, when an ALB serves a web app on port 443, its certificate often leaks backend infrastructure details that Nmap alone cannot reveal. Memory tip: SANs are like a backstage pass—they show you the internal names the server trusts, not just the public stage name.
PT0-002 Practice Question: Information Gathering and Vulnerability Scanning
This PT0-002 practice question tests your understanding of information gathering and vulnerability scanning. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 an external assessment against a client's web application hosted on an AWS EC2 instance behind an Application Load Balancer (ALB). The tester has performed passive reconnaissance and identified the public IP of the ALB, but the web application is only accessible via a specific domain name. During active scanning, the tester runs Nmap against the public IP and only sees port 443 open. The tester then performs a DNS Zone Transfer attempt against the authoritative name servers, which fails. While reviewing the web application, the tester notices that the application sets a cookie with the path '/admin'. The tester suspects there is an internal subnet used for backend services. Which of the following techniques would be MOST effective to discover internal hostnames or IP ranges?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Examine SSL certificate Subject Alternative Names (SANs) in the certificate presented by the ALB.
Option D is correct because SSL certificates often include Subject Alternative Names (SANs) that list internal hostnames. Option A is impossible from outside the network; Option B requires internal access to the metadata service; Option C already failed.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Attempt a zone transfer against a different authoritative DNS server.
Why it's wrong here
The previous zone transfer attempt failed, and other servers likely have the same restrictions.
✓
Examine SSL certificate Subject Alternative Names (SANs) in the certificate presented by the ALB.
Why this is correct
Internal hostnames are often included in SANs for web servers.
Use the AWS Metadata Service to extract information about the underlying EC2 instance.
Why it's wrong here
The metadata service is only accessible from within the instance.
✗
Perform a ping sweep of the internal RFC 1918 addresses and look for responses.
Why it's wrong here
Ping sweeps cannot reach internal addresses from the external network.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PT0-002 subnetting questions on CIDR, address ranges, and subnet selection.
Information Gathering and Vulnerability Scanning — This question tests Information Gathering and Vulnerability Scanning — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Examine SSL certificate Subject Alternative Names (SANs) in the certificate presented by the ALB. — Option D is correct because SSL certificates often include Subject Alternative Names (SANs) that list internal hostnames. Option A is impossible from outside the network; Option B requires internal access to the metadata service; Option C already failed.
What should I do if I get this PT0-002 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PT0-002 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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