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CAS-004 Practice Question: Needs to implement a solution that will detect…
A security engineer needs to implement a solution that will detect and block command-and-control (C2) traffic from malware on the internal network. The solution must be able to inspect encrypted traffic and operate at the network layer. Which of the following is the BEST choice?
⚠ Common exam trap
It's easy for candidates to choose a network-based IDS/IPS (Option B) thinking it can inspect encrypted traffic, but without SSL/TLS decryption, it can only see encrypted payloads and cannot detect C2 commands hidden inside the encrypted tunnel.
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
✓
Deploy a next-generation firewall (NGFW) with SSL/TLS inspection and application-level filtering.
A next-generation firewall (NGFW) with SSL/TLS inspection and application-level filtering is the best choice because it can decrypt and inspect encrypted C2 traffic at the network layer, then apply application-aware rules to block malicious communications. This directly addresses the requirement to detect and block C2 traffic that uses encryption to evade traditional inspection.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Implement a web application firewall (WAF) to filter outbound HTTP/HTTPS traffic.
Why it's wrong here
A WAF inspects inbound application-layer HTTP requests to protect web apps; it does not decrypt arbitrary outbound C2 channels or operate at the network layer. It is tempting because it handles HTTP/HTTPS, and would be correct for shielding a public web application from injection and layer-7 attacks.
- ✗
Install a network-based intrusion detection/prevention system (IDS/IPS) with signature updates.
Why it's wrong here
Signature-based network IDS/IPS matches known patterns and cannot decrypt TLS, so encrypted C2 channels pass uninspected. It is tempting because signature IPS blocks known threats at the network layer, and would be correct for unencrypted traffic using documented indicators.
- ✗
Use endpoint detection and response (EDR) agents on all workstations and servers.
Why it's wrong here
EDR agents run on hosts, not at the network layer, so they cannot inspect and block encrypted traffic traversing the internal network. Host telemetry is tempting because it catches malware behaviour directly, and would be correct if the requirement were endpoint-level detection and response rather than network inspection.
- ✓
Deploy a next-generation firewall (NGFW) with SSL/TLS inspection and application-level filtering.
Why this is correct
An NGFW with SSL/TLS inspection decrypts encrypted sessions, then applies application-level filtering to identify and block C2 signatures at the network layer. This satisfies both constraints: inspecting encrypted traffic and operating inline at the network layer.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CAS-005 exam.