Question 103 of 509

Attacks and Exploits →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is DNS tunneling, specifically encoding the payload in Base64 and using DNS queries to execute commands. This technique succeeds because DNS tunneling encapsulates non-DNS traffic, such as reverse shell commands and their output, within standard DNS query and response packets on UDP port 53, which the outbound firewall explicitly allows. By making malicious traffic appear as legitimate DNS lookups, the tester bypasses the firewall’s block on all other ports, effectively establishing a covert command-and-control channel. On the CompTIA PenTest+ PT0-002 exam, this scenario tests your understanding of protocol abuse and application-layer evasion—a common trap is assuming you need to open a new port or use HTTP, but the firewall only permits DNS. Remember the mnemonic: “DNS doesn’t deny data; it delivers it.”

PT0-002 Attacks and Exploits Practice Question

This PT0-002 practice question tests your understanding of attacks and exploits. 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 has gained a foothold on a Linux server through a vulnerable web application. The server has an outbound firewall that blocks all traffic except DNS queries (UDP 53). The tester needs to establish a reverse shell to maintain access. Which technique is most likely to succeed?

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.

Question 1hardmultiple choice

Read the full DNS explanation →

A
Use a bind shell on a high TCP port and connect from the tester's machine
Why wrong: The bind shell would listen on a port, but the outbound firewall on the server does not restrict inbound connections; however, the tester would need to connect to the server. But the firewall allows outbound DNS only, so the server cannot initiate a connection back. This approach is not suitable.
B
Encode the payload in Base64 and use DNS tunneling to execute commands
DNS tunneling can encode arbitrary data within DNS queries, which are allowed through the firewall, and can be used to establish a two-way communication channel, enabling a reverse shell.
C
Attempt a reverse shell over HTTP using TCP port 80
Why wrong: The firewall blocks all outbound traffic except DNS (UDP 53), so a connection on TCP port 80 would be blocked.
D
Use SSH reverse port forwarding to the tester's server on port 443
Why wrong: SSH requires a TCP connection, which would be blocked by the firewall. DNS tunneling does not rely on a direct TCP connection to the tester's server.

Full breakdown with real-world context →

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

✓

Encode the payload in Base64 and use DNS tunneling to execute commands

Option B is correct because DNS tunneling encapsulates non-DNS traffic (e.g., command output) within DNS query and response packets, which are allowed through the firewall on UDP port 53. This technique bypasses the outbound firewall restriction by making the malicious traffic appear as legitimate DNS queries, enabling the tester to execute commands and exfiltrate data without triggering network-level blocks.

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.

✗
Use a bind shell on a high TCP port and connect from the tester's machine
Why it's wrong here
The bind shell would listen on a port, but the outbound firewall on the server does not restrict inbound connections; however, the tester would need to connect to the server. But the firewall allows outbound DNS only, so the server cannot initiate a connection back. This approach is not suitable.
✓
Encode the payload in Base64 and use DNS tunneling to execute commands
Why this is correct
DNS tunneling can encode arbitrary data within DNS queries, which are allowed through the firewall, and can be used to establish a two-way communication channel, enabling a reverse shell.
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.
✗
Attempt a reverse shell over HTTP using TCP port 80
Why it's wrong here
The firewall blocks all outbound traffic except DNS (UDP 53), so a connection on TCP port 80 would be blocked.
✗
Use SSH reverse port forwarding to the tester's server on port 443
Why it's wrong here
SSH requires a TCP connection, which would be blocked by the firewall. DNS tunneling does not rely on a direct TCP connection to the tester's server.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume a reverse shell over HTTP (TCP 80) will work because HTTP is commonly allowed, but the question explicitly states the firewall blocks all traffic except DNS queries (UDP 53), making TCP-based reverse shells fail regardless of the port.

Detailed technical explanation

How to think about this question

DNS tunneling works by encoding payload data (e.g., Base64-encoded commands) into the subdomain field of a DNS query (e.g., <encoded-payload>.attacker.com), which is sent to the tester's controlled DNS server. The server decodes the query, executes the command, and encodes the response in the DNS answer (e.g., TXT record), allowing bidirectional communication over UDP 53. In real-world scenarios, this technique is often used for command-and-control (C2) in restricted networks, but it can be detected by analyzing DNS query sizes or frequency anomalies.

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 SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this PT0-002 question test?

Attacks and Exploits — This question tests Attacks and Exploits — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Encode the payload in Base64 and use DNS tunneling to execute commands — Option B is correct because DNS tunneling encapsulates non-DNS traffic (e.g., command output) within DNS query and response packets, which are allowed through the firewall on UDP port 53. This technique bypasses the outbound firewall restriction by making the malicious traffic appear as legitimate DNS queries, enabling the tester to execute commands and exfiltrate data without triggering network-level blocks.

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: "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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