hardMultiple ChoiceObjective-mapped
CAS-004 Practice Question: A security analyst is reviewing the following…
A security analyst is reviewing the following JSON Web Token (JWT) header: {"alg":"none","typ":"JWT"}. Which of the following vulnerabilities does this indicate?
⚠ Common exam trap
CompTIA often tests the misconception that 'none' algorithm is about encryption or key strength, when in fact it is a direct signature bypass that enables algorithm confusion attacks.
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
✓
Algorithm confusion attack surface
The JWT header specifies `"alg":"none"`, which instructs the server to accept a token without any cryptographic signature. This is a critical vulnerability because an attacker can forge arbitrary tokens by setting the algorithm to `none`, bypassing signature verification entirely. The correct answer is B because this directly creates an algorithm confusion attack surface, where the server may be tricked into accepting unsigned tokens.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Weak signing key
Why it's wrong here
A weak signing key would require a signature algorithm, but 'none' means no signature is used.
- ✓
Algorithm confusion attack surface
Why this is correct
The 'none' algorithm allows attackers to bypass verification, a known JWT vulnerability.
- ✗
Token expiration not set
Why it's wrong here
The header does not contain expiration information; it only shows algorithm and type.
- ✗
Unencrypted payload
Why it's wrong here
JWT payloads are base64-encoded, not encrypted; this is expected and not a vulnerability.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 practice question is part of Courseiva's free CompTIA 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 CAS-005 exam.