Linux shellcode sample

Linux shellcode sample

HelloWorld.nasm

;HelloWorld.asm
;Author: Kul Subedi

global _start

section .text
    _start:
        ; print HelloWorld! in screen
        mov eax, 0x4
        mov ebx, 0x1
        mov ecx, message
        ;mov edx, 12
        mov edx, mlen
        int 0x80

        ; exit program gracefully
        mov eax, 0x1
        mov ebx, 0x5
        int 0x80

section .data
    message: db "Welcome to Assembly!"
    mlen equ $-message

 

abc.nasm

;hello.asm
[SECTION .text]

global _start


_start:

        jmp short call_shellcode

        shellcode:

        xor eax, eax    ;clean up the registers
        xor ebx, ebx
        xor edx, edx
        xor ecx, ecx

        mov al, 4       ;syscall write
        mov bl, 1       ;stdout is 1
        pop ecx         ;get the address of the string from the stack
        mov dl, 5       ;length of the string
        int 0x80

        xor eax, eax
        mov al, 1       ;exit the shellcode
        xor ebx,ebx
        int 0x80

        call_shellcode:
        call shellcode	;put the address of the string on the stack
        db 'milu'

compile.sh

#!/usr/bin/env bash

echo '[+] Assembling with Nasm .. '
nasm -f elf32 -o $1.o $1.nasm
echo '[+] Linking ... '
ld -o $1 $1.o
echo '[+] Done!'

 

shel.sh

#!/usr/bin/env bash

objdump -d $1 | grep '[0-9a-f]:' | grep -v 'file' | cut -d: -f2|cut -d' ' -f1-6 | tr -s ' ' | tr '\t' ' ' | sed 's/ $//g' | sed 's/ /\\x/g' | paste -d '' -s | sed 's/^/"/' | sed 's/$/"/g'

abctxt.txt

"\xeb\x19\x31\xc0\x31\xdb\x31\xd2\x31\xc9\xb0\x04\xb3\x01\x59\xb2\x05\xcd\x80\x31\xc0\xb0\x01\x31\xdb\xcd\x80\xe8\xe2\xff\xff\xff\x6d\x69\x6c\x75"

shellcode.c

#include <stdio.h>
#include <string.h>

unsigned char code[] ="\xeb\x19\x31\xc0\x31\xdb\x31\xd2\x31\xc9\xb0\x04\xb3\x01\x59\xb2\x05\xcd\x80\x31\xc0\xb0\x01\x31\xdb\xcd\x80\xe8\xe2\xff\xff\xff\x6d\x69\x6c\x75";

main(){
    printf("Shellcode Length: %d\n", strlen(code));

    int (*ret)() = (int(*)())code;

    ret();
}

gcc_compile.sh

#!/usr/bin/env bash

echo '[+] Compiling....'

gcc -fno-stack-protector -z execstack $1.c -o $1

echo '[+] Done...'

============== End