PCNSE Decryption and SSL Inspection Practice Question
This PCNSE practice question tests your understanding of decryption and ssl inspection. 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
Refer to the exhibit.
```
2019-03-21 10:15:33.456 ssl_decrypt: session 12345, error: ssl_decrypt_cert_verify_failed, reason: certificate has expired
```
Based on the exhibit, what is the most likely action for the firewall to take on this session?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Bypass decryption and allow the session to proceed.
The firewall is configured for SSL Forward Proxy decryption, but the server certificate is self-signed or otherwise untrusted (e.g., expired, mismatched CN). In such cases, the firewall cannot re-sign the certificate to establish a trusted decrypted session. The configured action for untrusted server certificates is 'bypass decryption,' which allows the session to proceed without decryption, logging the bypass. Option D is correct because the firewall will not block or drop the session by default when bypass is configured.
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.
✗
Re-issue a new certificate to the client.
Why it's wrong here
The firewall does not issue new certificates for server certificates.
✗
Block the session because the server certificate is invalid.
Why it's wrong here
The firewall can block if configured, but default is to bypass.
✗
Drop the session and log a security alert.
Why it's wrong here
Firewalls drop only if a security policy rule blocks; decryption failures typically result in bypass.
✓
Bypass decryption and allow the session to proceed.
Why this is correct
Default behavior is to bypass when certificate verification fails.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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 often assume an invalid server certificate always results in a block or drop, but the firewall's behavior depends on the configured 'untrusted certificate action' in the decryption policy, which can be set to bypass.
Detailed technical explanation
How to think about this question
In Palo Alto Networks SSL Forward Proxy decryption, when the server certificate is untrusted (e.g., self-signed, expired, or from an untrusted CA), the firewall cannot complete the re-signing process because it would be signing an invalid certificate. The 'untrusted certificate action' setting in the decryption policy determines behavior: 'bypass' allows the original SSL handshake to proceed without decryption, while 'block' drops the session and logs a security alert. This is distinct from the 'block expired certificate' option, which only applies to valid but expired certificates, not to self-signed or otherwise untrusted ones.
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 practitioner preparing for the PCNSE exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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 SSL Inspection — This question tests Decryption and SSL Inspection — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Bypass decryption and allow the session to proceed. — The firewall is configured for SSL Forward Proxy decryption, but the server certificate is self-signed or otherwise untrusted (e.g., expired, mismatched CN). In such cases, the firewall cannot re-sign the certificate to establish a trusted decrypted session. The configured action for untrusted server certificates is 'bypass decryption,' which allows the session to proceed without decryption, logging the bypass. Option D is correct because the firewall will not block or drop the session by default when bypass is configured.
What should I do if I get this PCNSE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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