- A
Java deserialization of untrusted data (RCE via Commons Collections).
The presence of Commons Collections provides known gadget chains (e.g., ysoserial) that can achieve code execution during deserialization, making this the direct attack vector.
- B
SQL injection.
Why wrong: While SQL injection is a common web vulnerability, the scenario specifically describes a deserialization endpoint, not a SQL query. SQL injection would require a different entry point.
- C
Cross-site scripting.
Why wrong: XSS is a client-side attack that runs in the browser, not server-side code execution. It cannot achieve RCE on the server through deserialization.
- D
Command injection.
Why wrong: Command injection exploits improper sanitization of user input in system shell commands. Deserialization is a different class of vulnerability, though both can lead to RCE.
Quick Answer
The answer is Java deserialization of untrusted data (RCE via Commons Collections) because the vulnerable endpoint combined with the Apache Commons Collections library creates a classic gadget chain attack. When an attacker sends a malicious serialized object, the deserialization process triggers methods like InvokerTransformer from Commons Collections, which use Java reflection to execute arbitrary system commands—this is the core mechanism behind CVE-2015-7501. On the CompTIA PenTest+ PT0-002 exam, this scenario tests your ability to recognize how common libraries can become attack vectors; a common trap is assuming any deserialization flaw is limited to denial of service, when in fact the presence of Commons Collections enables full remote code execution. Memory tip: think "Commons Collections = Command Execution" because the library's transform methods turn serialized data into system calls.
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 discovers that a web application uses a vulnerable Java deserialization endpoint. The classpath includes the Apache Commons Collections library. Which attack technique is most likely to achieve remote code execution?
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.
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
Java deserialization of untrusted data (RCE via Commons Collections).
The correct answer is A because the presence of the Apache Commons Collections library in the classpath, combined with a vulnerable Java deserialization endpoint, enables the classic 'gadget chain' attack. Attackers craft a malicious serialized object that, when deserialized, invokes methods in Commons Collections (e.g., InvokerTransformer) to execute arbitrary system commands, achieving remote code execution (RCE). This is a well-documented exploit chain (e.g., CVE-2015-7501) that directly leverages the library's reflection-based classes.
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.
- ✓
Java deserialization of untrusted data (RCE via Commons Collections).
Why this is correct
The presence of Commons Collections provides known gadget chains (e.g., ysoserial) that can achieve code execution during deserialization, making this the direct attack vector.
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.
- ✗
SQL injection.
Why it's wrong here
While SQL injection is a common web vulnerability, the scenario specifically describes a deserialization endpoint, not a SQL query. SQL injection would require a different entry point.
- ✗
Cross-site scripting.
Why it's wrong here
XSS is a client-side attack that runs in the browser, not server-side code execution. It cannot achieve RCE on the server through deserialization.
- ✗
Command injection.
Why it's wrong here
Command injection exploits improper sanitization of user input in system shell commands. Deserialization is a different class of vulnerability, though both can lead to RCE.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse deserialization attacks with other input-based attacks like SQLi or XSS, failing to recognize that the specific vulnerability is the unsafe deserialization of Java objects using a known gadget library (Commons Collections) to achieve server-side RCE.
Trap categories for this question
Command / output trap
Command injection exploits improper sanitization of user input in system shell commands. Deserialization is a different class of vulnerability, though both can lead to RCE.
Scenario analysis trap
While SQL injection is a common web vulnerability, the scenario specifically describes a deserialization endpoint, not a SQL query. SQL injection would require a different entry point.
Detailed technical explanation
How to think about this question
The exploit works by chaining classes like `InvokerTransformer`, `ChainedTransformer`, and `TransformedMap` from Commons Collections to call `Runtime.exec()` via reflection. A subtle behavior is that the gadget chain must avoid triggering exceptions during deserialization; tools like `ysoserial` generate payloads that carefully order transformers to bypass `readObject()` validation. In real-world scenarios, even if the application uses a custom `ObjectInputStream`, the chain can still succeed if it does not filter known dangerous classes.
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
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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: Java deserialization of untrusted data (RCE via Commons Collections). — The correct answer is A because the presence of the Apache Commons Collections library in the classpath, combined with a vulnerable Java deserialization endpoint, enables the classic 'gadget chain' attack. Attackers craft a malicious serialized object that, when deserialized, invokes methods in Commons Collections (e.g., InvokerTransformer) to execute arbitrary system commands, achieving remote code execution (RCE). This is a well-documented exploit chain (e.g., CVE-2015-7501) that directly leverages the library's reflection-based classes.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on PT0-002
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A penetration tester discovers a web application that deserializes user-controlled data without validation. The application uses Java serialization. The tester creates a malicious serialized object that executes a system command. Which of the following conditions is required for this exploit to succeed?
medium- A.The application must be running with root privileges
- B.The application must use a custom ClassLoader
- ✓ C.The Java runtime must have a gadget chain available in its classpath
- D.The application must be running on a Windows operating system
Why C: Java deserialization exploits rely on the presence of specific classes (gadget chains) in the application's classpath that can be chained together to achieve arbitrary code execution. The attacker crafts a serialized object that, when deserialized, triggers a sequence of method calls (gadget chain) that ultimately executes a system command. Without a suitable gadget chain available in the classpath, the deserialization of a malicious object will not lead to code execution.
Variation 2. A penetration tester discovers a Java application that deserializes user-controlled data without validation. The tester crafts a malicious serialized object that executes a command upon deserialization. The application runs on a Linux server with a standard Java runtime. Which of the following is the most likely outcome if the malicious object is accepted?
medium- A.The application will crash immediately due to an exception.
- B.The application will disclose sensitive information in the response.
- C.The tester will gain a shell with the privileges of the current user.
- ✓ D.The tester will be able to execute arbitrary commands on the server.
Why D: Java deserialization of untrusted data allows an attacker to supply a crafted serialized object that, when deserialized, can execute arbitrary code via gadget chains (e.g., CommonsCollections). Since the application runs on a Linux server with a standard Java runtime, the attacker can achieve remote code execution (RCE) with the privileges of the application's user, not necessarily an interactive shell. Option D is correct because the primary impact is arbitrary command execution, which may or may not yield a shell depending on the payload.
Last reviewed: Jun 11, 2026
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