ICMP Type 3 Protocol Encapsulation: Nested ICMP Firewall Bypass & DPI Evasion via 0xFFFF Boundary Flaw
Stateful firewalls and DPI engines classify ICMP Type 3 (Port Unreachable) as error traffic and skip deep inspection. RFC 792 requires the original IP header plus 8 bytes in the reflection field — this is attacker-controlled space. By placing a fully-formed secondary ICMP header inside the reflection segment, arbitrary protocol data traverses perimeter controls unanalyzed. The 0xFFFF boundary anomaly causes packet boundary miscalculation in DPI engines, leaving the nested payload invisible to signature matching. Full x64 Assembly implementation with raw socket crafting.
