CEH v13 identifies encrypted communication channels as one of the most common and effective firewall evasion techniques. Firewalls that rely on packet inspection or signature-based filtering often cannot inspect encrypted payloads without SSL/TLS interception capabilities.
By encrypting malicious traffic-using HTTPS, VPN tunnels, or encrypted C2 channels-attackers can bypass firewall rules that inspect packet contents. CEH v13 emphasizes that this technique is widely used in malware communication, data exfiltration, and command-and-control operations.
IP spoofing (Option A) is limited by ingress and egress filtering and is less effective against modern firewalls.
Open-source operating systems (Option B) do not inherently evade firewalls. Social engineering (Option D) targets users, not firewalls.
Therefore, Option C is the correct and CEH-aligned answer.