Refer to the exhibit.

Exact Extract: “Next, they will use SSH tunneling to bypass firewall rules that prevent LAN devices from accessing some devices in the SOC network. They will be able to gain access to crucial network infrastructure.”

The correct answer is D. Protocol tunneling. The exhibit shows the compromised PC using SSH to connect to a permitted intermediary system—the engineering build server—and then using that path to relay HTTPS traffic toward internal servers that the LAN host could not normally access directly. That is tunneling: one protocol or traffic flow is encapsulated or relayed through another allowed channel to bypass segmentation or firewall policy.

A is wrong because port knocking is a stealth access-control mechanism where a sequence of connection attempts opens a port. B is wrong because the exhibit is about reaching internal servers, not stealing data through an established C2 channel. C is wrong because there is no interception or manipulation of traffic between two victims; the build server is being used as a pivot/tunnel.

Technical Deep Dive: In MITRE terms, this behavior aligns with tunneling/proxy-style defense evasion and lateral movement support. In real operations, an attacker may use SSH local forwarding, remote forwarding, or dynamic SOCKS proxying, for example ssh -L 8443:internal-server:443 user@build-server or ssh -D 1080 user@build-server. From a Fortinet SOC perspective, FortiSIEM should flag unusual SSH sessions from workstations to build servers, followed by unexpected HTTPS connections from the build server to protected server zones. FortiGate NP/CP offload may accelerate allowed sessions, but the detection value comes from log correlation and segmentation policy violations, not ASIC behavior.