PCNSA Decryption and Monitoring Practice Question
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?
⚠ Common exam trap
A common mix-up: 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.
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
✓
Use a decryption profile that allows sessions with certificate status unknown.
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.
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCNSA practice question is part of Courseiva's free Palo Alto Networks 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 PCNSA exam.