Quick Answer
The answer is that the CA certificate has not been added to the browser’s trusted root store, even though it was installed on the operating system. This is correct because browsers like Firefox maintain their own independent certificate store, separate from the OS store; Chrome uses the system store but still requires the certificate to be properly placed in the OS trust list. On the Fortinet NSE 4 exam, this scenario tests your understanding of SSL inspection deployment pitfalls—specifically that installing a CA on the client OS does not guarantee browser trust. A common trap is assuming the OS store is always sufficient, but Firefox’s isolated store is a frequent cause of the “certificate not trusted” warning. Remember the memory tip: “OS installs, but Firefox insists”—meaning you must manually import the CA into Firefox’s certificate manager for it to trust the inspection certificate.
This NSE4 practice question tests your understanding of security profiles. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
After enabling SSL inspection, a user receives a warning 'The certificate is not trusted' in the browser. The administrator has installed the CA certificate on the client. What else could be the cause?
The firewall policy denies the traffic.
Why wrong: If denied, no warning would appear.
The CA certificate is not added to the browser's trusted root store.
The CA must be trusted by the browser.
The FortiGate is not decrypting the traffic.
Why wrong: If not decrypting, no certificate error would appear.
The web server's certificate has expired.
Why wrong: That would cause a different error, but the FortiGate re-signs.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The CA certificate is not added to the browser's trusted root store.
Even though the administrator installed the CA certificate on the client, the browser uses its own trusted root store, which is separate from the operating system's certificate store. If the CA certificate is not specifically added to the browser's trusted root store (e.g., Chrome uses the system store but Firefox maintains its own), the browser will still flag the certificate as untrusted. This is a common misconfiguration when deploying SSL inspection with FortiGate.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The firewall policy denies the traffic.
Why it's wrong here
If denied, no warning would appear.
The CA certificate is not added to the browser's trusted root store.
Why this is correct
The CA must be trusted by the browser.
Related concept
Read the scenario before looking for a memorised answer.
The FortiGate is not decrypting the traffic.
Why it's wrong here
If not decrypting, no certificate error would appear.
The web server's certificate has expired.
Why it's wrong here
That would cause a different error, but the FortiGate re-signs.
Common exam traps
The trap here is that candidates assume installing the CA certificate on the client OS is sufficient for all browsers, but browsers like Firefox maintain their own certificate trust store, and even Chrome on some platforms may require the certificate to be in the correct store (e.g., the 'Trusted Root Certification Authorities' store) for the warning to disappear.
Detailed technical explanation
When FortiGate performs SSL inspection, it intercepts the TLS handshake, generates a new certificate on-the-fly signed by the FortiGate's CA, and presents it to the client. The client browser must trust the FortiGate's CA certificate; if it is not in the browser's trust store (or the OS store, depending on the browser), the browser will display a trust warning. Some browsers like Firefox use their own certificate store (NSS database) independent of the OS, requiring manual import of the CA certificate into Firefox's store even if it is installed system-wide.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the NSE4 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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Profiles — study guide chapter
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FAQ
Security Profiles — This question tests Security Profiles — Read the scenario before looking for a memorised answer..
The correct answer is: The CA certificate is not added to the browser's trusted root store. — Even though the administrator installed the CA certificate on the client, the browser uses its own trusted root store, which is separate from the operating system's certificate store. If the CA certificate is not specifically added to the browser's trusted root store (e.g., Chrome uses the system store but Firefox maintains its own), the browser will still flag the certificate as untrusted. This is a common misconfiguration when deploying SSL inspection with FortiGate.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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