- A
Replace Java serialization with JSON serialization using a library like Jackson, and configure it to disallow polymorphic deserialization by default.
This eliminates the insecure deserialization vector by using a safer serialization format and disabling dangerous features.
- B
Use a Web Application Firewall (WAF) to block requests containing known deserialization payloads.
Why wrong: WAF rules are reactive and can be bypassed by novel or obfuscated payloads; they do not fix the underlying vulnerability.
- C
Implement a custom deserialization filter using ObjectInputFilter to whitelist only expected classes.
Why wrong: While filtering can help, it is error-prone and may not cover all classes; also, it does not address the fundamental risk of Java deserialization.
- D
Encrypt all serialized objects using AES-256 before sending them to the client.
Why wrong: Encryption protects data in transit but does not prevent deserialization attacks because the decrypted data is still deserialized.
Quick Answer
The answer is to replace Java serialization with JSON serialization using a library like Jackson, configured to disallow polymorphic deserialization by default. This is the most effective insecure deserialization mitigation because it eliminates the root cause—Java’s native serialization mechanism, which can automatically execute arbitrary code when deserializing untrusted data. JSON serialization with strict type handling prevents attackers from injecting malicious objects, providing a sustainable fix that doesn’t rely on fragile blacklists or encryption that fails to address the underlying vulnerability. On the CISSP exam, this scenario tests your understanding of secure design principles and the Software Development Security domain, where the key trap is mistaking encryption or WAFs for true remediation—they only obscure or block symptoms, not the flaw itself. Remember the mnemonic: “Replace, don’t wrap”—swap out the dangerous mechanism entirely rather than layering controls over it.
CISSP Software Development Security Practice Question
This CISSP practice question tests your understanding of software development security. 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 financial services company uses a custom web application for online banking. The application is developed in-house using Java and deployed on Apache Tomcat servers. Recently, the security team discovered that the application is vulnerable to a critical remote code execution (RCE) vulnerability due to insecure deserialization of untrusted data. The vulnerability exists in a module that processes session objects. The development team has been assigned to fix this issue. They propose the following options:
A. Implement a custom deserialization filter using ObjectInputFilter to whitelist only expected classes. B. Replace Java serialization with JSON serialization using a library like Jackson, and configure it to disallow polymorphic deserialization by default. C. Encrypt all serialized objects using AES-256 before sending them to the client. D. Use a Web Application Firewall (WAF) to block requests containing known deserialization payloads.
The application must maintain high availability and minimal latency. Which option provides the MOST effective and sustainable remediation?
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
Replace Java serialization with JSON serialization using a library like Jackson, and configure it to disallow polymorphic deserialization by default.
Option A is correct because replacing Java serialization with JSON serialization (e.g., Jackson) and disabling polymorphic deserialization eliminates the root cause of insecure deserialization—Java's native serialization mechanism that automatically executes arbitrary code when deserializing untrusted data. JSON serialization with strict type handling prevents the attacker from injecting malicious objects, providing a sustainable fix without relying on fragile blacklists or encryption that doesn't address the vulnerability.
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.
- ✓
Replace Java serialization with JSON serialization using a library like Jackson, and configure it to disallow polymorphic deserialization by default.
Why this is correct
This eliminates the insecure deserialization vector by using a safer serialization format and disabling dangerous features.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a Web Application Firewall (WAF) to block requests containing known deserialization payloads.
Why it's wrong here
WAF rules are reactive and can be bypassed by novel or obfuscated payloads; they do not fix the underlying vulnerability.
- ✗
Implement a custom deserialization filter using ObjectInputFilter to whitelist only expected classes.
Why it's wrong here
While filtering can help, it is error-prone and may not cover all classes; also, it does not address the fundamental risk of Java deserialization.
- ✗
Encrypt all serialized objects using AES-256 before sending them to the client.
Why it's wrong here
Encryption protects data in transit but does not prevent deserialization attacks because the decrypted data is still deserialized.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose encryption (Option D) thinking it secures the data in transit, but encryption does not address the deserialization logic flaw—the vulnerability remains after decryption, and the attacker can still trigger RCE if they control the serialized stream.
Detailed technical explanation
How to think about this question
Java serialization uses the ObjectInputStream.readObject() method, which can instantiate arbitrary classes and invoke their readObject() or readResolve() methods, enabling RCE via gadget chains (e.g., Commons Collections). JSON libraries like Jackson, when configured with default typing disabled or using @JsonTypeInfo with explicit allowlists, prevent polymorphic deserialization attacks (e.g., 'gadget chains' like those exploiting log4j or Spring). In real-world incidents, such as the 2015 Apache Commons Collections vulnerability, replacing serialization with safer formats like JSON or Protocol Buffers was the recommended long-term fix.
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.
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 CISSP question test?
Software Development Security — This question tests Software Development Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Replace Java serialization with JSON serialization using a library like Jackson, and configure it to disallow polymorphic deserialization by default. — Option A is correct because replacing Java serialization with JSON serialization (e.g., Jackson) and disabling polymorphic deserialization eliminates the root cause of insecure deserialization—Java's native serialization mechanism that automatically executes arbitrary code when deserializing untrusted data. JSON serialization with strict type handling prevents the attacker from injecting malicious objects, providing a sustainable fix without relying on fragile blacklists or encryption that doesn't address the vulnerability.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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 →
Last reviewed: Jun 11, 2026
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.
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