Easily Debug Shellcode for Windows x64 and x86-32
2022-06-03 Dawid Farbaniec


The injectable code called shellcode is position independent code.
Just as pentesters, red teams and threat actors write shellcodes, in opposite malware analysts, blue teams and others responsible for cybersecurity often analyze such codes under the debugger.
The BytesLauncher solution is a handy application that allows to easily run shellcode for Windows x64 and older 32-bit (x86) architecture under the debugger. This quick solution was developed when encountering shellcode in the malware sample.
Just as pentesters, red teams and threat actors write shellcodes, in opposite malware analysts, blue teams and others responsible for cybersecurity often analyze such codes under the debugger.
The BytesLauncher solution is a handy application that allows to easily run shellcode for Windows x64 and older 32-bit (x86) architecture under the debugger. This quick solution was developed when encountering shellcode in the malware sample.
BytesLauncher for Windows x64
The program was created in MASM x64 and one can use Visual Studio to build it.extrn ExitProcess : proc
extrn VirtualProtect : proc
extrn CreateFileA : proc
extrn ReadFile : proc
extrn CloseHandle : proc
.const
GENERIC_READ equ 080000000h
OPEN_EXISTING equ 03h
PAGE_EXECUTE_READWRITE equ 40h
.data
payload db 2048 dup (90h) ;change size if you need
oldProtect dword 0
dwReadWritten dword 0
hFile dword 0
szPath db "C:\Users\x\Desktop\dump1.bin", 0
.code
Main proc
sub rsp, 38h
mov qword ptr [rsp + 30h], 0
mov qword ptr [rsp + 28h], 0
mov qword ptr [rsp + 20h], OPEN_EXISTING
xor r9, r9
xor r8, r8
mov rdx, GENERIC_READ
mov rcx, offset szPath
call CreateFileA
mov hFile, eax
mov qword ptr [rsp + 20h], 0
mov r9, offset dwReadWritten
mov r8, sizeof payload
mov rdx, offset payload
mov ecx, hFile
call ReadFile
mov ecx, hFile
call CloseHandle
mov r10, sizeof payload
mov r9, offset oldProtect
mov r8, PAGE_EXECUTE_READWRITE
mov rdx, r10
mov rcx, offset payload
call VirtualProtect
mov rax, offset payload
call rax
xor rcx, rcx
call ExitProcess
Main endp
end
BytesLauncher for Windows x86 (legacy 32-bit)
The program was created in MASM x86 (32-bit) and one can use Visual Studio or MASM32 SDK to build it..686p
.model flat, stdcall
option casemap:none
ExitProcess proto stdcall :dword
VirtualProtect proto stdcall :dword,:dword,:dword,:dword
CreateFileA proto stdcall :dword, :dword, :dword, :dword, :dword, :dword, :dword
ReadFile proto stdcall :dword, :dword, :dword, :dword, :dword
CloseHandle proto stdcall :dword
.const
GENERIC_READ equ 080000000h
OPEN_EXISTING equ 03h
.data
payload db 2048 dup (90h) ;change size if you need
oldProtect dword 0
dwReadWritten dword 0
hFile dword 0
szPath db "C:\Users\x\Desktop\dump1.bin", 0
.code
Main proc
push 0
push 0
push OPEN_EXISTING
push 0
push 0
push GENERIC_READ
push offset szPath
call CreateFileA
mov hFile, eax
push 0
push offset dwReadWritten
push sizeof payload
push offset payload
push eax
call ReadFile
push hFile
call CloseHandle
push offset oldProtect
push 40h ;PAGE_EXECUTE_READWRITE
push sizeof payload
push offset payload
call VirtualProtect
mov eax, offset payload
call eax ;execute payload bytes
push 0
call ExitProcess
Main endp
end
Bibliography
https://ethical.blue/download/BytesLauncher-MASM-x64.zip [access: 2022-09-24]https://github.com/ethicalblue/BytesLauncher [access: 2022-05-23]