Gray Hat Hacking, Second Edition, 2nd Edition

Basic Linux Shellcode

The term “shellcode” refers to self-contained binary code that completes a task. The task may range from issuing a system command to providing a shell back to the attacker, as was the original purpose of shellcode.

There are basically three ways to write shellcode:

• Directly write the hex opcodes.

• Write a program in a high level language like C, compile it, and then disassemble it to obtain the assembly instructions and hex opcodes.

• Write an assembly program, assemble the program, and then extract the hex opcodes from the binary.

Writing the hex opcodes directly is a little extreme. We will start with learning the C approach, but quickly move to writing assembly, then to extraction of the opcodes. In any event, you will need ...