Question 248 of 509

Attacks and Exploits →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is to create a malicious executable named 'dirname' in a directory earlier in the PATH. This is correct because the setuid script uses `BASEDIR=$(dirname $0)`, which calls the external `dirname` command; by manipulating the PATH environment variable, an attacker can force the shell to execute a rogue `dirname` binary they control instead of the legitimate system utility. On the CompTIA PenTest+ PT0-002 exam, this technique tests your understanding of how setuid scripts inherit the user’s environment, including PATH, and how even a seemingly safe internal variable can be exploited. A common trap is assuming the script’s use of `$0` is secure, but the real vulnerability lies in the external command resolution. Memory tip: "If the script calls a command, check if you can hijack its path—setuid doesn't sanitize your environment."

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 gained low-privileged access to a Linux server and found that the user can run a custom script located at /opt/tool/backup.sh with setuid root. The script begins with a hashbang #!/bin/bash and uses an internal variable defined as BASEDIR=$(dirname $0) to determine paths. Which technique is most likely to allow privilege escalation?

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 1mediummultiple choice

Read the full NAT/PAT explanation →

A
Modify the $0 variable during execution
Why wrong: $0 is read-only in most contexts and cannot be modified by environment variables; the attacker cannot change it from outside.
B
Create a malicious executable named 'dirname' in a directory earlier in the PATH
Since the script uses $(dirname $0) without an absolute path, the system searches PATH for 'dirname'. If the attacker puts a malicious 'dirname' script in a writable directory earlier in PATH, it will be executed as root.
C
Overwrite /opt/tool/backup.sh with a reverse shell
Why wrong: Overwriting requires write permission on the script file, which the low-privileged user likely does not have.
D
Exploit a buffer overflow in the Bash interpreter
Why wrong: Buffer overflows in Bash are extremely rare and not applicable to this simple script scenario.

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

✓

Create a malicious executable named 'dirname' in a directory earlier in the PATH

Option B is correct because the script uses `BASEDIR=$(dirname $0)` to resolve paths. If the user can place a malicious executable named `dirname` earlier in the PATH than the legitimate `/usr/bin/dirname`, then when the script runs with setuid root, the shell will execute the attacker's `dirname` binary instead, allowing arbitrary code execution as root.

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.

✗
Modify the $0 variable during execution
Why it's wrong here
$0 is read-only in most contexts and cannot be modified by environment variables; the attacker cannot change it from outside.
✓
Create a malicious executable named 'dirname' in a directory earlier in the PATH
Why this is correct
Since the script uses $(dirname $0) without an absolute path, the system searches PATH for 'dirname'. If the attacker puts a malicious 'dirname' script in a writable directory earlier in PATH, it will be executed as root.
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.
✗
Overwrite /opt/tool/backup.sh with a reverse shell
Why it's wrong here
Overwriting requires write permission on the script file, which the low-privileged user likely does not have.
✗
Exploit a buffer overflow in the Bash interpreter
Why it's wrong here
Buffer overflows in Bash are extremely rare and not applicable to this simple script scenario.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates may focus on modifying `$0` (Option A) or overwriting the script (Option C), but the actual vulnerability lies in the insecure use of a relative command (`dirname`) within a setuid script, which allows PATH hijacking.

Trap categories for this question

Scenario analysis trap
Buffer overflows in Bash are extremely rare and not applicable to this simple script scenario.

Detailed technical explanation

How to think about this question

The `dirname` command is resolved by the shell using the PATH environment variable. By placing a malicious `dirname` in a world-writable directory (e.g., `/tmp`) and prepending that directory to PATH (e.g., `export PATH=/tmp:$PATH`), the attacker hijacks the command. This is a classic example of a PATH injection attack, which is especially dangerous when the script runs with elevated privileges via setuid. In real-world scenarios, even hardened systems can be vulnerable if scripts use relative command names without absolute paths.

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.

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: Create a malicious executable named 'dirname' in a directory earlier in the PATH — Option B is correct because the script uses `BASEDIR=$(dirname $0)` to resolve paths. If the user can place a malicious executable named `dirname` earlier in the PATH than the legitimate `/usr/bin/dirname`, then when the script runs with setuid root, the shell will execute the attacker's `dirname` binary instead, allowing arbitrary code execution as root.

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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