Convert a Compiled C Program to shellcode (Hex)

Question

So I wanted to convert a compiled C program into Hex format so that I can inject it inside the memory. The problem I am currently facing is that I have no idea how to convert a compiled C file to hex. Can someone show me how it's done?

My C Code (temp.c):

#include <stdio.h>

void main(){
printf("Working!");
}

Compiled it using gcc: gcc -g temp.c -o temp -m32

Answer 1

You can write in assembly using write(); syscall and exit(); syscall.

Here code I wrote, file w.asm :

global _start
section .text

_start:

    push    byte  0x0a    
    push    dword "ing!"
    push    dword "Work"
    inc     ebx
    mov     ecx, esp
    mov     dl, 9
    mov     al, 4
    int     0x80

    xor     ebx, ebx
    mov     al, 1
    int     0x80

Assembling and linking using nasm and ld :

nasm -f elf w.asm && ld -o w w.o

Dump binary file into hex (shellcode style) using objdump one-liner like this:

objdump -d ./w | grep '[0-9a-f]:'|grep -v 'file'|cut -f2 -d:|cut -f1-6 -d' '|tr -s ' '|tr '\t' ' '|sed 's/ $//g'|sed 's/ /\\x/g'|paste -d '' -s |sed 's/^/"/'|sed 's/$/"/g' 

You will get the result like this:

"\x6a\x0a\x68\x69\x6e\x67\x21\x68\x57\x6f\x72\x6b\x43\x89\xe1\xb2\x09\xb0\x04\xcd\x80\x31\xdb\xb0\x01\xcd\x80"