C / C++ / MFC

How can I prevent a user from accessing my ISAPI extension directly from his browser?

I have an ISAPI extension that can be accessed by the URL - <nobr>[http://www.mysite.com/scripts/myisapi.dll?query=value]

I access the extension from an asp page through a form submit request. Now my problem is that anybody smart enough to decipher the url and the query string that needs to be provided to the extension can access it successfully. I would want to prevent this access. How can I go about achieving this?

pmsg = malloc (cLinesMax * sizeof (MSG));

error C2440: '=' : cannot convert from 'void *' to 'struct tagMSG *'
        Conversion from 'void*' to pointer to non-'void' requires an explicit cast

/*------------------------------------------------------------------------
	keyview1.cpp -- Displays keyboard and character messages
                        Paul Lyons, December 30, 2001
                       (C) Charles Petzold, Programming Windows
  ----------------------------------------------------------------------*/

/*
 *	Inculdes
 */
#include <windows.h>

/*
 *	Function Prototypes
 */
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

/*
 *	Program entry point
 */
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                   PSTR szCmdLine, int iCmdShow)
{
	/*
	 *	Variable declarations
	 */
	static TCHAR szAppName[] = TEXT("KeyView1");
	HWND         hwnd;
	MSG          msg;
	WNDCLASS     wndclass;

	/*
	 *	Define wndclass
	 */
	wndclass.style         = CS_HREDRAW | CS_VREDRAW;
	wndclass.lpfnWndProc   = WndProc;
	wndclass.cbClsExtra    = 0;
	wndclass.cbWndExtra    = 0;
	wndclass.hInstance     = hInstance;
	wndclass.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
	wndclass.hCursor       = LoadCursor(NULL, IDC_ARROW);
	wndclass.lpszMenuName  = NULL;
	wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
	wndclass.lpszClassName = szAppName;

	/*
	 *	Register window class
	 */
	if (!RegisterClass (&wndclass))
	{
		MessageBox(NULL, TEXT("This application requires WinNT to run."),
                             szAppName, MB_ICONERROR);
		return 0;
	}

	/*
	 *	Create window
	 */
	hwnd = CreateWindow(szAppName, TEXT("Keyboard Message Viewer #1"),
                             WS_OVERLAPPEDWINDOW,
                             CW_USEDEFAULT, CW_USEDEFAULT,
                             CW_USEDEFAULT, CW_USEDEFAULT,
                             NULL, NULL, hInstance, NULL);

	/*
	 *	Display window
	 */
	ShowWindow(hwnd, iCmdShow);
	UpdateWindow(hwnd);

	/*
	 *	Message loop
	 */
	while (GetMessage(&msg, NULL, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

	return msg.wParam;
}

/************************************************************************/
/*                            WndProc                                   */
/************************************************************************/
LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
                         WPARAM wParam, LPARAM lParam)
{
	static int   cxClientMax, cyClientMax;
	static int   cxClient, cyClient;
	static int   cxChar, cyChar;
	static int   cLinesMax, cLines;
	static PMSG  pmsg;
	static RECT  rectScroll;
	static TCHAR szTop[] = TEXT("Message            Key         Char     ")
                                 TEXT("    Repeat Scan Ext ALT  Prev  Tran");
	static TCHAR szUnd[] = TEXT("-------            ---         ----     ")
                               TEXT("    ------ ---- --- ---  ----  ----");

	static TCHAR* szFormat[2] = {

		TEXT("%-13s %3d %-15s%c%6u %4d %3s %3s %4s %4s"),
		TEXT("%-13s            0x%04x%1s%c %6u %4d %3s %3s %4s %4s")	};
	
	static TCHAR* szYes  = TEXT("Yes");
	static TCHAR* szNo   = TEXT("No");
	static TCHAR* szDown = TEXT("Down");
	static TCHAR* szUp   = TEXT("Up");

	static TCHAR* szMessage[] = {TEXT("WM_KEYDOWN"),    TEXT("WM_KEYUP"),
                                      TEXT("WM_CHAR"),       TEXT("WM_DEADCHAR"),
                                      TEXT("WM_SYSKEYDOWN"), TEXT("WM_SYSKEYUP"),
                                      TEXT("WM_SYSCHAR"),    TEXT("WM_SYSDEADCHAR") };


	HDC         hdc;
	int         i, iType;
	PAINTSTRUCT ps;
	TCHAR       szBuffer[128], szKeyName[32];
	TEXTMETRIC  tm;

	switch (message)
	{
	case WM_CREATE:
	case WM_DISPLAYCHANGE:

	        // Get the maximum size of the client area
	        cxClientMax = GetSystemMetrics(SM_CXMAXIMIZED);
	        cyClientMax = GetSystemMetrics(SM_CYMAXIMIZED);

	        // Get character size for fixed pitch font
	        hdc = GetDC(hwnd);

	        SelectObject(hdc, GetStockObject(SYSTEM_FIXED_FONT));
		GetTextMetrics(hdc, &tm);
		cxChar = tm.tmAveCharWidth;
		cyChar = tm.tmHeight;

		ReleaseDC(hwnd, hdc);

		// Allocate memory for display lines
		if (pmsg)
			free (pmsg);

		cLinesMax = cyClientMax / cyChar;
		pmsg = malloc (cLinesMax * sizeof (MSG));
		cLines = 0;

		// Fall through...

	case WM_SIZE:
		if (message == WM_SIZE)
		{
			cxClient = LOWORD(lParam);
			cyClient = HIWORD(lParam);
		}

		// Calculate the scrolling rectangle
		rectScroll.left = 0;
		rectScroll.right = cxClient;
		rectScroll.top = cyChar;
		rectScroll.bottom = cyChar * (cyClient / cyChar);

		InvalidateRect(hwnd, NULL, TRUE);
		return 0;

	case WM_KEYDOWN:
	case WM_KEYUP:
	case WM_CHAR:
	case WM_DEADCHAR:
	case WM_SYSKEYDOWN:
	case WM_SYSKEYUP:
	case WM_SYSCHAR:
	case WM_SYSDEADCHAR:

		// Rearrange the storage array
		for (i = cLinesMax - 1; i > 0; i--)
		{
			pmsg[i] = pmsg[i - 1];
		}

		// Store new message
		pmsg[0].hwnd	 = hwnd;
		pmsg[0].message = message;
		pmsg[0].wParam  = wParam;
		pmsg[0].lParam  = lParam;

		cLines = min(cLines + 1, cLinesMax);

		// Scroll up the display
		ScrollWindow(hwnd, 0, -cyChar, &rectScroll, &rectScroll);

		// Call the DefWindowProc so system messages work
		break;


	case WM_PAINT:
		hdc = BeginPaint(hwnd, &ps);

		SelectObject(hdc, GetStockObject(SYSTEM_FIXED_FONT));
		SetBkMode(hdc, TRANSPARENT);
		TextOut(hdc, 0, 0, szTop, lstrlen(szTop));
		TextOut(hdc, 0, 10, szUnd, lstrlen(szUnd));

		for (i = 0; i < min(cLines, cyClient / cyChar - 1); i++)
		{
			iType = pmsg[i].message == WM_CHAR ||
				 pmsg[i].message == WM_SYSCHAR ||
				 pmsg[i].message == WM_DEADCHAR ||
				 pmsg[i].message == WM_SYSDEADCHAR;

			GetKeyNameText(pmsg[i].lParam, szKeyName, sizeof(szKeyName) / sizeof(TCHAR));

			TextOut(hdc, 0, (cyClient / cyChar - 1 - i) * cyChar, szBuffer,
			wsprintf(szBuffer, szFormat[iType],
                         szMessage[pmsg[i].message - WM_KEYFIRST],
                         (PSTR) (iType ? TEXT(" ") : szKeyName),
                         (TCHAR) (iType ? pmsg[i].wParam : ' '),
                         LOWORD (pmsg[i].lParam),
                         HIWORD (pmsg[i].lParam) & 0xFF,
                         0x10000000 & pmsg[i].lParam ? szYes : szNo,
                         0x20000000 & pmsg[i].lParam ? szYes : szNo,
                         0x40000000 & pmsg[i].lParam ? szDown : szUp,
                         0x80000000 & pmsg[i].lParam ? szUp : szDown));
		}
		EndPaint(hwnd, &ps);
		return 0;


	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	}

	return DefWindowProc(hwnd, message, wParam, lParam);
}

class CTaskManager  
{
public:
	CTaskManager ();
	virtual ~CTaskManager ();
protected:
	CString m_sSharedVars [MAX_VARS];
        
        ...
};

void CTaskManager::ReplaceVariables (CString &str)
{
	for (int i = 0 ; i < MAX_VARS ; i++)
	{
		if (m_sSharedVarNames [i] != m_sSharedVars [i])
		{
			while (str.Replace (m_sSharedVarNames [i], m_sSharedVars [i]) != 0);
		}
	}
}

<br />
The intruction at "0x5f47714c" referenced memeory at "0xcdcdcde1". The memory could not be "read". <br />
Click on OK to terminate the program<br />
Click on Cancel to debug the program<br />

<br />
_AFX_INLINE CString::operator LPCTSTR() const<br />
	{ return m_pchData; }<br />

<br />
Unhandled exception in MyProgram.exe (MFC42D.DLL):0xC0000005:Access Violation<br />