The answer is to use a decryption profile that allows sessions with certificate status unknown. This resolves the decryption failure certificate status unknown issue because the firewall’s revocation checking cannot reach the CRL or OCSP responder for those specific educational sites, leaving the certificate’s validity indeterminate. The current profile blocks sessions with expired certificates and untrusted issuers, but it does not explicitly block sessions where the revocation status is unknown, so the intermittent failures stem from the firewall rejecting the handshake when it cannot verify revocation. On the PCNSA exam, this scenario tests your understanding of SSL decryption profiles and how certificate validation failure can occur even when the root CA is properly installed—a common trap is to assume the root CA is missing or that the certificate is expired. Remember the memory tip: “Unknown status needs a permissive profile, not a missing root.”
PCNSA Decryption and Monitoring Practice Question
This PCNSA practice question tests your understanding of decryption and monitoring. 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 university uses a Palo Alto firewall for outbound SSL decryption. The IT helpdesk receives complaints that students cannot access certain educational resource websites (e.g., online libraries, research databases) after decryption was enabled. The firewall logs show 'decryption failure' for these sites with reason 'certificate validation failure'. The decryption profile is set to 'Block sessions with expired certificates' and 'Block sessions with untrusted issuers'. The helpdesk verifies that the root CA certificate is installed on all endpoints. The issue is intermittent and only affects a few sites. What should the administrator do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a decryption profile that allows sessions with certificate status unknown.
The correct answer is D because the 'decryption failure' with 'certificate validation failure' and 'certificate status unknown' indicates that the firewall cannot determine the revocation status of the site's certificate (e.g., no CRL or OCSP responder reachable). The current decryption profile blocks sessions with expired certificates and untrusted issuers, but it does not explicitly block sessions with 'certificate status unknown'. By using a decryption profile that allows sessions with certificate status unknown, the firewall will permit the SSL handshake to proceed even when revocation checking fails, resolving the intermittent access issues for those specific educational sites.
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.
✗
Update the firewall's certificate revocation list (CRL).
Why it's wrong here
CRL updates address revocation, but the error is certificate validation failure, not necessarily revoked certs.
✗
Add the websites to a decryption policy exception rule.
Why it's wrong here
Excluding the sites from decryption removes visibility and defeats the purpose of decryption.
✗
Disable blocking for untrusted issuers in the decryption profile.
Why it's wrong here
This would allow all untrusted certificates, which is a broad change that may introduce security risks.
✓
Use a decryption profile that allows sessions with certificate status unknown.
Why this is correct
Intermittent validation failures often stem from unreachable CRL/OCSP; allowing unknown status lets the firewall decrypt the session.
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 status unknown' with 'untrusted issuer' or 'expired certificate', leading them to choose options that disable broader security controls (like untrusted issuer blocking) instead of the specific setting that addresses the revocation check failure.
Detailed technical explanation
How to think about this question
In Palo Alto firewalls, the decryption profile's 'Certificate Status Unknown' setting controls behavior when the firewall cannot verify a certificate's revocation status via CRL or OCSP. When this option is set to 'allow', the firewall permits the session even if the revocation check fails, which is common for sites using self-signed certificates or those with unreachable OCSP responders. This is distinct from 'Block sessions with expired certificates' and 'Block sessions with untrusted issuers', which handle different failure modes. In real-world scenarios, educational resource sites often use certificates from internal CAs or have misconfigured revocation endpoints, leading to intermittent 'unknown' status.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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.
Decryption and Monitoring — This question tests Decryption and Monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a decryption profile that allows sessions with certificate status unknown. — The correct answer is D because the 'decryption failure' with 'certificate validation failure' and 'certificate status unknown' indicates that the firewall cannot determine the revocation status of the site's certificate (e.g., no CRL or OCSP responder reachable). The current decryption profile blocks sessions with expired certificates and untrusted issuers, but it does not explicitly block sessions with 'certificate status unknown'. By using a decryption profile that allows sessions with certificate status unknown, the firewall will permit the SSL handshake to proceed even when revocation checking fails, resolving the intermittent access issues for those specific educational sites.
What should I do if I get this PCNSA 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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