- A
Add the custom application to a security rule with action Deny.
Why wrong: Incorrect. Adding a custom application to a security rule with Deny requires the traffic to first be identified as that application. Without proper identification (via custom signature or override), the rule will not match.
- B
Disable SSL decryption on the firewall.
Why wrong: Incorrect. Disabling SSL decryption does not help identify the malware; it may reduce visibility. App-ID can identify applications based on handshake patterns without decryption.
- C
Create a custom application signature that matches the malware handshake.
Correct. A custom application signature matches the malware's unique handshake, allowing App-ID to correctly identify it despite using port 443.
- D
Create a decryption policy to forward proxy decrypt the traffic.
Why wrong: Incorrect. Decryption policy is for decrypting SSL traffic, not for identification. App-ID works on handshake characteristics even without decryption.
- E
Create an application override rule that forces identification as the custom application.
Correct. After creating the custom signature, an application override rule forces the firewall to apply that custom application identification to the traffic, enabling subsequent security rules to block it.
Custom App-ID Signature for Malware Identification Without SSL Decryption
This PCNSE practice question tests your understanding of securing traffic and app-id. 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.
During a security incident, an analyst notices that certain malware traffic is using port 443 but is being identified as 'ssl'. The malware uses a unique handshake that differs from standard SSL. Which two actions should the analyst take to correctly identify and block this malware? (Choose two.)
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
Create a custom application signature that matches the malware handshake.
Options C and E are correct. Creating a custom application signature (C) enables the firewall to identify the malware based on its unique handshake, bypassing the default SSL identification. Then, creating an application override rule (E) forces the firewall to treat the traffic as that custom application, allowing it to match a security rule with action Deny. Option A is incorrect because without identification, a security rule cannot block the traffic. Option B is incorrect as disabling decryption prevents visibility into encrypted payloads. Option D is incorrect because decryption is not required for identification via App-ID.
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.
- ✗
Add the custom application to a security rule with action Deny.
Why it's wrong here
Incorrect. Adding a custom application to a security rule with Deny requires the traffic to first be identified as that application. Without proper identification (via custom signature or override), the rule will not match.
- ✗
Disable SSL decryption on the firewall.
Why it's wrong here
Incorrect. Disabling SSL decryption does not help identify the malware; it may reduce visibility. App-ID can identify applications based on handshake patterns without decryption.
- ✓
Create a custom application signature that matches the malware handshake.
Why this is correct
Correct. A custom application signature matches the malware's unique handshake, allowing App-ID to correctly identify it despite using port 443.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a decryption policy to forward proxy decrypt the traffic.
Why it's wrong here
Incorrect. Decryption policy is for decrypting SSL traffic, not for identification. App-ID works on handshake characteristics even without decryption.
- ✓
Create an application override rule that forces identification as the custom application.
Why this is correct
Correct. After creating the custom signature, an application override rule forces the firewall to apply that custom application identification to the traffic, enabling subsequent security rules to block it.
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 assume SSL decryption is required to inspect or block SSL-encrypted malware, but App-ID can identify applications based on handshake characteristics without decryption, and a custom signature or application override is the correct approach.
Detailed technical explanation
How to think about this question
App-ID uses multiple mechanisms to identify applications, including protocol decoding, SSL/TLS handshake analysis, and application signatures. For custom malware that uses a non-standard SSL handshake, a custom application signature can be defined using the Application Signature Editor, which allows matching on specific byte sequences, offsets, or regular expressions within the handshake. An application override rule forces the firewall to treat traffic matching certain criteria (e.g., IP, port) as a specific application, bypassing App-ID's normal identification process, which is useful when the malware's traffic cannot be reliably identified by signature alone.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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FAQ
Questions learners often ask
What does this PCNSE question test?
Securing Traffic and App-ID — This question tests Securing Traffic and App-ID — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a custom application signature that matches the malware handshake. — Options C and E are correct. Creating a custom application signature (C) enables the firewall to identify the malware based on its unique handshake, bypassing the default SSL identification. Then, creating an application override rule (E) forces the firewall to treat the traffic as that custom application, allowing it to match a security rule with action Deny. Option A is incorrect because without identification, a security rule cannot block the traffic. Option B is incorrect as disabling decryption prevents visibility into encrypted payloads. Option D is incorrect because decryption is not required for identification via App-ID.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
7 more ways this is tested on PCNSE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses App-ID to identify traffic on their Palo Alto Networks firewall. They notice that a particular application, custom-db-sync, is not being identified correctly. The traffic uses a proprietary protocol over TCP port 4444. The firewall currently has a security rule allowing any application on that port. Which step should the engineer take to enable App-ID to correctly identify custom-db-sync?
medium- ✓ A.Create a custom App-ID for custom-db-sync using the Application Object and define the appropriate signatures.
- B.Enable unknown application identification in the security rule.
- C.Use the default application override for port 4444 to allow traffic.
- D.Change the security rule to use 'application-default' as the service to rely on port-based identification.
Why A: Option A is correct because App-ID relies on application signatures to identify traffic, not just port numbers. Since custom-db-sync uses a proprietary protocol over TCP 4444, the firewall cannot match it to any built-in App-ID. Creating a custom App-ID with appropriate signatures (e.g., protocol decoders, pattern matches) allows the firewall to correctly identify this custom application, enabling policy enforcement beyond port-based rules.
Variation 2. Which TWO of the following are valid methods to create a custom App-ID on a Palo Alto Networks firewall?
medium- A.Right-clicking on a session in the Traffic log and selecting 'Create App-ID'.
- B.Using the 'Application Command Center' to automatically generate custom App-IDs.
- ✓ C.Using the 'set application' command in the CLI.
- D.Importing an App-ID definition file from a CSV.
- ✓ E.Using the 'Objects' > 'Application Filters' menu in the web interface.
Why C: Option C is correct because the 'set application' CLI command allows you to define a custom App-ID by specifying characteristics such as protocol, port, and signature. This is a direct method to create a custom application object on a Palo Alto Networks firewall, as documented in the administrator's guide.
Variation 3. Which THREE attributes can be used in a custom App-ID signature to identify an application? (Choose three.)
hard- ✓ A.Protocol (TCP, UDP, etc.)
- ✓ B.Port number
- ✓ C.Data pattern (regular expression or byte sequence)
- D.URL category
- E.Security policy action
Why A: A is correct because the protocol (TCP, UDP, etc.) is a fundamental attribute used in custom App-ID signatures to define the transport layer over which the application traffic flows. The firewall uses this to match the signature against the correct protocol type, ensuring accurate application identification.
Variation 4. During a security audit, it is discovered that a custom application signature matches too broadly, causing benign traffic to be classified as the custom app. What change should be made to narrow the signature?
hard- A.Remove the protocol field from the signature.
- B.Use a wider port range and remove data patterns.
- ✓ C.Add a data pattern filter to match a specific payload signature.
- D.Expand the port range to include more traffic.
Why C: Option C is correct because adding a data pattern filter allows the custom App-ID signature to match on a specific payload string or byte sequence, which narrows the scope of traffic classified as that application. Without a data pattern, the signature may rely solely on IP protocol, port, or other broad criteria, causing false positives. By requiring a unique payload signature, only traffic containing that exact data pattern is identified as the custom application.
Variation 5. A large enterprise uses a custom application that communicates over TCP port 8080 using HTTP. The application traffic is correctly identified as 'custom-app' by App-ID. Recently, the development team changed the application to use HTTPS on the same port. The firewall administrator updated the security policy to allow the application, using the same application name, but now the traffic is being denied. The firewall logs show the application as 'ssl' and the action 'deny'. The security policy has a rule that allows 'custom-app' from inside to outside. What should the administrator do to resolve this issue?
medium- A.Create an application override for the traffic on port 8080.
- B.Disable App-ID for that traffic and use a port-based policy.
- C.Change the security policy rule to allow application 'ssl' instead.
- ✓ D.Update the custom application definition to include SSL decryption and a hostname match.
Why D: The correct answer is D. Since the application changed from HTTP to HTTPS on the same port, App-ID now identifies it as 'ssl' instead of 'custom-app' because the traffic is encrypted. To have App-ID recognize the encrypted traffic as the custom application, the administrator must update the custom application definition to include SSL decryption (so the firewall can inspect the encrypted payload) and a hostname match (to distinguish this specific application from other SSL traffic). This allows the existing security policy rule that allows 'custom-app' to match the traffic. Option A is incorrect because an application override would bypass App-ID entirely, reducing visibility and security. Option B is incorrect because disabling App-ID and using port-based policy loses application awareness and security. Option C is incorrect because changing the rule to allow 'ssl' would permit all SSL traffic on port 8080, which is overly permissive and a security risk.
Variation 6. A company uses a custom application for internal VoIP traffic. The custom App-ID signature is configured with the correct protocol and port, but traffic is still not matching. The firewall shows the application as 'unknown-tcp'. What should the administrator check next?
medium- A.Verify that the port range in the custom application is correct.
- B.Update the App-ID signature database.
- C.Check for asymmetric routing on the firewall.
- ✓ D.Ensure a protocol decoder (e.g., SIP) is enabled for the application.
Why D: Custom App-ID signatures require a protocol decoder to inspect application-layer payloads. Even if the port and protocol are correctly defined, without an enabled decoder (e.g., SIP for VoIP), the firewall cannot identify the application and falls back to 'unknown-tcp'. Enabling the appropriate decoder allows the firewall to parse the traffic and match the custom signature.
Variation 7. A company has an application signature for an internal ERP system that uses a proprietary protocol over TCP port 4444. The ERP traffic is sometimes misidentified as unknown-tcp. Which App-ID mechanism should be used to improve identification without affecting the default App-ID engine?
medium- A.Configure a port-based application override for port 4444.
- B.Enable SSL decryption for the ERP traffic.
- ✓ C.Create a custom application with a data pattern (signature).
- D.Create an application override to allow the traffic without App-ID.
Why C: Option C is correct because creating a custom application with a data pattern (signature) allows the firewall to identify the ERP traffic based on its unique payload characteristics, without overriding or disabling the default App-ID engine. This approach uses a custom App-ID signature that matches the proprietary protocol's data pattern, ensuring accurate identification while the default engine continues to process other traffic normally.
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Last reviewed: Jul 4, 2026
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