From bytecode to bytes: automated magic packet generation

This post introduces a tool that uses symbolic execution and the Z3 theorem prover to automatically generate magic packets capable of triggering BPF-based Linux backdoors.

• •Classic BPF socket programs are embedded in the Linux kernel and used by malware like BPFDoor to stay dormant until a specific magic packet is received
• •BPFDoor, linked to China-based threat actors, monitors all incoming traffic without requiring an open port, targeting telecoms, education, and government sectors
• •A BFS queue-based shortest path algorithm identifies the minimum-condition execution path through BPF bytecode that leads to packet acceptance
• •Z3 models each BPF load and conditional jump as symbolic constraints and solves for the exact byte values satisfying the acceptance path
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