The answer is that an application control profile set to 'allow' for the matching application is overriding the IPS block action, causing the log to show 'pass'. This occurs because in FortiOS, application control processing happens before IPS inspection; when the application control profile permits the traffic, the IPS engine never enforces its block action, resulting in a 'pass' log entry despite the signature match. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this scenario tests your understanding of security profile evaluation order and how application control override can silently bypass IPS rules—a common trap where administrators assume IPS alone governs all traffic. Remember the processing hierarchy: application control evaluates first, so an 'allow' there can negate a downstream IPS 'block'. Memory tip: "App allows first, IPS can't burst"—application control permits the flow before IPS ever gets to block it.
NSE4 Security Profiles Practice Question
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.
During a security audit, an administrator finds that an IPS sensor configured with a 'block' action for a critical vulnerability signature is not blocking the associated traffic. The traffic matches the signature, but the action appears as 'pass' in the logs. The IPS sensor is applied to a firewall policy that also has application control enabled. What is the most likely cause?
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
✓
Application control profile is set to 'allow' for the application associated with the traffic, overriding the IPS block action.
When an IPS sensor with a 'block' action logs 'pass' for matching traffic, it indicates that another security profile is overriding the IPS action. In FortiOS, if an application control profile is set to 'allow' for the application, it can bypass the IPS block because application control processing occurs before IPS inspection. The traffic is permitted by the application control profile, so the IPS engine does not enforce the block action, resulting in a 'pass' log entry.
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.
✓
Application control profile is set to 'allow' for the application associated with the traffic, overriding the IPS block action.
Why this is correct
Application control can override IPS if it allows the application, as it is evaluated after IPS in the policy flow.
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.
✗
The IPS engine is bypassed because the traffic matches a fast-path rule.
Why it's wrong here
Fast-path rules apply to certain protocols, but IPS is still applied.
✗
The IPS sensor is not enabled in the firewall policy.
Why it's wrong here
If the IPS sensor is applied to the policy, it is enabled.
✗
The IPS sensor is configured with 'monitor' action instead of 'block'.
Why it's wrong here
The question states the action is 'block' in the sensor, so this is not the cause.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume IPS block actions are absolute and independent of other security profiles, but FortiOS applies profiles in a strict sequence where application control can override IPS actions, causing the 'pass' log entry even when the signature matches.
Detailed technical explanation
How to think about this question
In FortiOS, the order of operations in a firewall policy is: application control, then IPS, then other security profiles. Application control can set a 'bypass' flag for traffic that matches an allowed application, causing subsequent IPS inspection to skip the block action and log the traffic as 'pass'. This is a deliberate design to avoid conflicting actions between profiles, and it is documented in the FortiOS Administration Guide under 'Security Profile Order'. In real-world scenarios, this often occurs when an organization wants to allow a specific application (e.g., a critical business app) but also apply IPS signatures for other threats, leading to unexpected bypasses if the application control profile is too permissive.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
Security Profiles — This question tests Security Profiles — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Application control profile is set to 'allow' for the application associated with the traffic, overriding the IPS block action. — When an IPS sensor with a 'block' action logs 'pass' for matching traffic, it indicates that another security profile is overriding the IPS action. In FortiOS, if an application control profile is set to 'allow' for the application, it can bypass the IPS block because application control processing occurs before IPS inspection. The traffic is permitted by the application control profile, so the IPS engine does not enforce the block action, resulting in a 'pass' log entry.
What should I do if I get this NSE4 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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