PCNSA Decryption and Monitoring Practice Question
A company implements SSL Forward Proxy decryption. Users report that some internal applications fail to load after deployment. The firewall is configured with a CA-signed certificate for decryption. What is the most likely cause of the application failures?
⚠ Common exam trap
Palo Alto Networks often tests the misconception that decryption failures are caused by policy misconfigurations or performance issues, rather than the fundamental requirement of installing the firewall's CA certificate on all client devices.
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
✓
The firewall's CA certificate is not installed in the trusted root store on user endpoints.
SSL Forward Proxy decryption requires the firewall's CA certificate to be trusted by client endpoints. When the firewall generates a new certificate for the internal application's server, the client must trust the firewall's CA to avoid certificate validation errors. Without the CA in the trusted root store, browsers and applications will reject the connection, causing failures for internal applications that rely on SSL/TLS.
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 decryption policy uses 'No Decrypt' for the internal application's URL category.
Why it's wrong here
'No Decrypt' for the internal application's URL category would let that traffic bypass inspection and load normally, so it cannot explain the failures. It is tempting because exclusions are the standard fix for broken decryption. This option is the remedy, not the cause; the stem describes applications failing after decryption was enabled.
- ✗
The decryption policy is set to 'Decrypt' for all traffic, causing performance bottlenecks.
Why it's wrong here
Decrypting all traffic does not by itself break application loading; it only adds inspection overhead. The failure stems from certificate trust, since internal apps present certificates the firewall cannot validate. A blanket decrypt policy is genuinely used when every flow must be inspected, but performance is not the mechanism causing these load failures.
- ✓
The firewall's CA certificate is not installed in the trusted root store on user endpoints.
Why this is correct
SSL Forward Proxy presents a certificate signed by the firewall's CA to endpoints. If that CA certificate is absent from endpoints' trusted root stores, certificate validation fails and internal applications relying on TLS cannot load, matching the reported failures.
- ✗
The firewall is configured to decrypt traffic from the internal zone, but not the external zone.
Why it's wrong here
SSL Forward Proxy decrypts traffic leaving the internal zone toward external servers; the external zone is not the relevant axis. Zone direction does not govern whether internal application certificates validate. Decrypting only the internal zone would be chosen to inspect outbound user traffic, which is precisely the forward proxy design here.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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