According to the CEH Network and Perimeter Security module, one of the most effective and widely used firewall evasion techniques is the use of encrypted communication channels. When traffic is encrypted using protocols such as HTTPS, TLS, or VPN tunnels, traditional firewalls and packet-inspection tools may be unable to inspect payload contents unless SSL/TLS inspection is explicitly enabled.

CEH documentation explains that attackers commonly encrypt command-and-control (C2) traffic to:

Blend in with legitimate encrypted traffic

Bypass content-based inspection

Evade signature-based detection

Option B is therefore correct.

Option A (IP spoofing) is less effective against stateful firewalls.

Option C is a human-focused attack, not firewall evasion.

Option D has no relevance to firewall bypass techniques.

CEH highlights encryption misuse as a major blind spot in perimeter defenses.