Author Topic: Importing WinAPI directly without externs  (Read 2070 times)

Offline dreamCoder

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Importing WinAPI directly without externs
« on: September 19, 2017, 08:30:37 PM »
Simple demo of directly importing WinAPI from source without extern. Probe starts from kernel32.dll.
This demo attempts to import MessageBoxA from user32.dll. Demo is not for beginners.

Code: [Select]
;<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
; Demo: Importing library directly
; nasm -f win64 demo.asm
; golink demo.obj
;>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
;Tested on Win10 only

global start

STARTING equ 0x10000

section .bss
AddrLoadLib     resq 1
AddrExitProcess resq 1
AddrGetProc     resq 1
AddrFreeLib     resq 1
BaseKernel      resq 1
imgExport       resq 1
AddrOfNames     resq 1
AddrOfFunctions resq 1
NumOfFunctions  resq 1

section .data
msg             db 'MessageBox from user32.dll',0
title           db 'by dreamCoder',0
_ExitProcess    db 'ExitProcess',0
_GetProcAddress db 'GetProcAddress',0
_LoadLibrary    db 'LoadLibraryA',0
_FreeLibrary    db 'FreeLibrary',0
_user32         db 'user32.dll',0
_MessageBoxA    db 'MessageBoxA',0
align 16

section .text
start:
        mov     rsi,[rsp]
        and     rsi,-STARTING
more:   mov     ax,word[rsi]
        cmp     ax,'MZ'
        je      good
        sub     rsi,STARTING
        jmp     more
good:   mov     [BaseKernel],rsi
        mov     ebx,dword[rsi+3ch]
        add     rsi,rbx
        add     rsi,4*6
        add     rsi,112
        mov     ebx,[rsi]
        mov     rax,[BaseKernel]
        add     rax,rbx
        mov     [imgExport],rax
        mov     ebx,[rax+4*6]
        mov     [NumOfFunctions],rbx
        add     rax,4*8
        mov     [AddrOfNames],rax
        mov     ebx,[rax]
        mov     rax,[BaseKernel]
        mov     ebx,[rsi]
        add     rax,rbx
        add     rax,4*7
        mov     [AddrOfFunctions],rax

        mov     rbx,_GetProcAddress
        call    GetAddress
        mov     [AddrGetProc],rax
        mov     rbx,_LoadLibrary
        call    GetAddress
        mov     [AddrLoadLib],rax
        mov     rbx,_ExitProcess
        call    GetAddress
        mov     [AddrExitProcess],rax
        mov     rbx,_FreeLibrary
        call    GetAddress
        mov     [AddrFreeLib],rax

        ;alignment + shadow space
        sub     rsp,40
        ;Load user32.dll
        mov     rcx,_user32
        call    [AddrLoadLib]
        mov     r15,rax
        ;MessageBoxA address
        mov     rdx,_MessageBoxA
        mov     rcx,rax
        call    [AddrGetProc]
        ;Run MessageBoxA
        mov     rcx,0
        mov     rdx,msg
        mov     r8,title
        mov     r9,0
        call    rax
        ;Run FreeLibrary
        mov     rcx,r15
        call    [AddrFreeLib]
        add     rsp,40
        ;Run ExitProcess
        mov     rcx,0
        call    [AddrExitProcess]


;In RBX: pointer to function string
;Ret   : RAX = Address of function
GetAddress:
        mov     rax,[AddrOfNames]
        mov     edx,[rax]
        mov     rax,[BaseKernel]
        add     rax,rdx
        mov     rcx,[NumOfFunctions]
        mov     rbx,[rbx]
        xor     esi,esi
Str:    mov     edx,[rax]
        add     rdx,[BaseKernel]
        mov     rcx,[rdx]
        cmp     rbx,rcx
        je      Addr
        add     rax,4
        add     rsi,1
        sub     rcx,1
        jnz     Str
Addr:   mov     rax,[imgExport]
        add     rax,4*7
        mov     ebx,[rax]
        mov     rax,[BaseKernel]
        add     rax,rbx
        mov     ecx,[rax+rsi*4]
        mov     rax,[BaseKernel]
        add     rax,rcx
        ret
« Last Edit: September 19, 2017, 08:39:54 PM by dreamCoder »

Offline dreamCoder

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Re: Importing WinAPI directly without externs
« Reply #1 on: September 23, 2017, 10:08:44 PM »
I updated the code to include more accurate string search. Download the source from the attachment provided.
The code is not much but it gives you total control in loading, linking and running a DLL alongside your code. Might be useful in shellcoding or reversing. This example loads msvcrt.dll and uses printf.



 


« Last Edit: September 23, 2017, 10:10:47 PM by dreamCoder »

Offline Dibya

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  • Posts: 19
Re: Importing WinAPI directly without externs
« Reply #2 on: September 25, 2017, 04:43:59 PM »
Thanks it is very helpful

Offline encryptor256

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Re: Importing WinAPI directly without externs
« Reply #3 on: November 16, 2017, 06:38:10 PM »
Hi dreamCoder.

Works great, but at the exit of the program:

ExitProcess throw's Access Violation Exception.

But works when I replace ExitProcess code with RET opcode.
Encryptor256's Investigation \ Research Department.