While conducting a penetration test, the tester determines that there is a firewall between the tester's machine and the target machine. The firewall is only monitoring TCP handshaking of packets at t

A packet filtering firewall operates at the network layer (Layer 3) and filters traffic based on IP addresses, ports, and protocols, not TCP session handshaking.

An application-level firewall (proxy firewall) operates at Layer 7 and inspects the full content of application traffic, going well beyond session-layer handshake monitoring.

A circuit-level gateway operates at the OSI session layer and validates TCP three-way handshakes to determine whether a requested session is legitimate, without inspecting the actual data payload. It acts as a relay for TCP connections, making it the firewall type that exclusively monitors TCP handshaking at the session layer as described in the question.

A stateful multilayer inspection firewall tracks connection state across multiple OSI layers simultaneously, not solely at the session layer.