The answer is that the client does not trust the CA that issued the server certificate, as indicated by the VPN certificate validation failure for an untrusted CA. This error occurs during the TLS handshake when the client’s trust store lacks the root certificate of the issuing Certificate Authority, preventing the server’s certificate chain from being verified—a fundamental breakdown in the Public Key Infrastructure trust model. On the CISSP exam, this scenario tests your grasp of PKI components and authentication failures, often appearing in domain 3 (Security Architecture and Engineering) as a trap to distinguish between certificate expiration, revocation, or a missing client certificate. A common pitfall is assuming the certificate is expired, but the log’s specific “unable to get local issuer certificate” message points solely to a missing trusted root. Memory tip: “No root, no route”—if the client cannot trace the chain to a trusted root, the VPN connection will fail.
CISSP Security Architecture and Engineering Practice Question
This CISSP practice question tests your understanding of security architecture and engineering. 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.
Exhibit
ERROR: Certificate verification failed: unable to get local issuer certificate
A user reports that a VPN client cannot connect to the corporate gateway. The exhibit shows an excerpt from the client log. What does this indicate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The client does not trust the CA that issued the server certificate
The client log indicates a certificate validation failure during the TLS handshake. The error 'unable to get local issuer certificate' or similar means the client cannot find a trusted root CA that issued the server's certificate. This is a classic PKI trust issue, not an expiration or missing client certificate problem.
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.
✗
The VPN server certificate is expired
Why it's wrong here
Incorrect. An expired certificate error would mention expiration.
✗
The server is using a self-signed certificate
Why it's wrong here
Incorrect. Self-signed certificates cause a different verification error.
✗
The client certificate is missing
Why it's wrong here
Incorrect. Missing client certificate would be a different error.
✓
The client does not trust the CA that issued the server certificate
Why this is correct
Correct. The error indicates the client cannot find the CA certificate.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'certificate expired' with 'untrusted CA' — both cause failures, but the log message and the underlying PKI process are different, and ISC2 often tests the distinction between trust chain errors and expiration errors.
Detailed technical explanation
How to think about this question
During the TLS handshake, the VPN server presents its certificate chain. The client performs path validation per RFC 5280: it checks each certificate's signature up to a trusted root. If the intermediate or root CA certificate is not in the client's trust store, the chain is broken and the handshake fails. This is distinct from certificate revocation (CRL/OCSP) or expiration checks, which occur after trust is established.
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 CISSP question in full detail.
Security Architecture and Engineering — This question tests Security Architecture and Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The client does not trust the CA that issued the server certificate — The client log indicates a certificate validation failure during the TLS handshake. The error 'unable to get local issuer certificate' or similar means the client cannot find a trusted root CA that issued the server's certificate. This is a classic PKI trust issue, not an expiration or missing client certificate problem.
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.
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Question Discussion
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