Summary

• Shellcode is small, position-independent, bad-byte-free machine code delivered as a payload.
• The execve("/bin/sh") pattern: set RAX/RDI/RSI/RDX, build the path on the stack, syscall.
• Get it via shellcraft/asm, msfvenom, or by hand.
• Injection needs a writable and executable region — which NX / W^{}X / DEP remove.
• Bad-char encoding fixes bytes, not executability; NX pushes real exploits toward ROP (Class 07).