CAS-004 Security Architecture Practice Question
During a threat modeling exercise for a new web application, the team identifies that the application uses JWT for authentication. Which vulnerability is most likely if the server does not properly verify the JWT signature?
⚠ Common exam trap
CAS-005 often tests whether candidates conflate authentication token weaknesses with generic web vulnerabilities (XSS, SQLi, IDOR), so the trap is picking a familiar OWASP Top 10 item instead of the token-specific flaw.
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
✓
JWT tampering
When a server fails to verify the JWT signature, an attacker can modify the token's payload (e.g., change the 'sub' or 'role' claim) and re-encode it without needing the signing key, because the server will accept any token whose signature it never validates. This is JWT tampering — the attacker forges or alters claims to impersonate another user or escalate privileges. The vulnerability is specific to improper cryptographic validation of the token, not to input handling or access control logic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Cross-site scripting
Why it's wrong here
Incorrect; XSS is a different vulnerability.
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SQL injection
Why it's wrong here
SQL injection stems from unsanitised input concatenated into database queries, which JWT signature verification does not govern. It is tempting because authentication flaws and injection both appear in OWASP guidance, but skipping signature checks yields forged tokens with attacker-controlled claims, not database query manipulation.
- ✓
JWT tampering
Why this is correct
Without signature verification, an attacker can alter JWT claims, such as changing a role or user identifier, and the server will accept the forged token. This is JWT tampering: the integrity guarantee fails because the signature is never validated against the signing key.
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Insecure direct object reference
Why it's wrong here
IDOR arises from missing authorisation checks on object identifiers, not from JWT signature validation. It is tempting because both are access-control flaws, yet the concrete mechanism here is that an unsigned or altered token is accepted as authentic, letting an attacker impersonate any user or escalate claims.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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.