Workstation unlocker

stdafx.h

#pragma once

#define WIN32_LEAN_AND_MEAN
#include "targetver.h"
#include <stdio.h>
#include <tchar.h>
#include <windows.h>

WinlogonUnlocker.cpp

#include "stdafx.h"

#define WM_LOGONNOTIFY			0x004c
#define LN_UNLOCK_WORKSTATION	0x0006

void showError()
{
	LPTSTR pBuf;
	DWORD nBytes = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
					NULL, GetLastError(), LANG_USER_DEFAULT, (LPWSTR)&pBuf, 4096, NULL);
	if (nBytes)
		wprintf(L"Error: %s", pBuf);
	else
		wprintf(L"Failed to format error message: %08x\n", GetLastError());
}

BOOL CALLBACK enumWndProc(HWND hWnd, HWND *hSasWindow)
{
	LPTSTR lpClassName[64];
	if (!GetClassName(hWnd, (LPTSTR)&lpClassName, 63))
		return TRUE;
	if (wcscmp((LPTSTR)lpClassName, L"SAS window class") != 0)
		return TRUE;
	*hSasWindow = hWnd;
	return FALSE;
}

int _tmain(int argc, _TCHAR* argv[])
{
	HDESK hDesktop = NULL;
	HWND hSasWindow = NULL;
	hDesktop = OpenDesktop(L"Winlogon", 0, FALSE, DESKTOP_READOBJECTS | DESKTOP_ENUMERATE);
	if (!hDesktop) {
		showError();
		return 1;
	}
	EnumDesktopWindows(hDesktop, (WNDENUMPROC)enumWndProc, (LPARAM)&hSasWindow);
	if (!hSasWindow) {
		wprintf(L"Error: WinLogon window not found.\n");
		return 1;
	}
	PostMessage(hSasWindow, WM_LOGONNOTIFY, LN_UNLOCK_WORKSTATION, 0);
	wprintf(L"Success: Unlock message sent to %p\n", hSasWindow);
	return 0;
}

Works on Windows XP when run with some psexec magic (tell psexec to run it on the secure logon desktop).