The correct answer is authentication bypass. This attack works because setting the JWT algorithm to 'none' removes all cryptographic verification, so if the server fails to validate the signature, it will accept a token with an arbitrary payload, allowing an attacker to impersonate any user without knowing the secret key. On the CompTIA PenTest+ PT0-002 exam, this scenario tests your understanding of insecure JWT implementations, often appearing in web application exploitation questions where the server trusts the header's algorithm field. A common trap is assuming the server always enforces signature verification, but many frameworks default to accepting 'none' if not explicitly disabled. Remember the memory tip: "No key, no problem—if the server doesn't check, you can forge any claim."
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 is testing a web application that uses JSON Web Tokens (JWTs) for authentication. The tester discovers that the server does not verify the JWT signature properly. The tester crafts a JWT with an arbitrary payload and sets the algorithm to 'none'. Which attack does this enable?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Authentication bypass
Option C is correct because setting the JWT algorithm to 'none' removes all cryptographic verification. If the server does not validate the signature, it will accept a token with an arbitrary payload, allowing the attacker to impersonate any user without knowing the secret key. This directly results in an authentication bypass, as the server trusts the forged token.
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.
✗
SQL injection
Why it's wrong here
The JWT signature flaw does not involve database query manipulation; it targets authentication logic.
✗
Server-side request forgery
Why it's wrong here
SSRF exploits server-side requests to internal resources, not JWT token verification.
✓
Authentication bypass
Why this is correct
Setting the algorithm to 'none' and forging the token allows the attacker to bypass authentication and gain unauthorized access.
Related concept
Read the scenario before looking for a memorised answer.
✗
Cross-site request forgery
Why it's wrong here
CSRF tricks a user into making unintended requests; it does not exploit JWT signature verification.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse JWT algorithm manipulation with injection attacks (SQLi) or server-side request forgery (SSRF), but the core of this question is about signature verification failure leading to authentication bypass.
Detailed technical explanation
How to think about this question
The JWT 'none' algorithm attack exploits a flaw in the JWT library where the server fails to enforce a whitelist of accepted algorithms. Under the hood, the token's header contains `"alg":"none"` and the signature is omitted; if the server's verification code does not reject unsigned tokens, it treats the payload as valid. In real-world scenarios, this was famously used against vulnerable implementations in libraries like `jsonwebtoken` before version 8.5.1, where the `jwt.verify()` method would accept 'none' if the secret was null.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PT0-002 question in full detail.
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: Authentication bypass — Option C is correct because setting the JWT algorithm to 'none' removes all cryptographic verification. If the server does not validate the signature, it will accept a token with an arbitrary payload, allowing the attacker to impersonate any user without knowing the secret key. This directly results in an authentication bypass, as the server trusts the forged token.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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