CreateProcess Access Denied when invoked by sticky keys - c++

Question

My program is designed to be a secure Sticky Keys hack. If sticky keys is invoked from logon, it will ask for a username and password to a local account. If they are correct, an instance of cmd.exe will be invoked as that user to avoid damage. When I double-click the sethc program from explorer,
It runs successfully.
When I run the same program with pressing shift five times,
It fails with error 5 Access Denied.
I can verify that sethc is run under winlogon when shift is pressed five times.
The whole file is:
// cmd.cpp : Defines the entry point for the console application.
//
#include <Windows.h>
#include <Lmcons.h>
#include <iostream>
#include <ctype.h>
#include <string>
#include <stdio.h>
#define winstring LPWSTR
#define stcas(x) static_cast<x>
#define INFO_BUFFER_SIZE 260
using namespace std;
void ReportError(LPCWSTR pszFunction, DWORD dwError = GetLastError())
{
wprintf(L"%s failed w/err 0x%08lx\n", pszFunction, dwError);
system("pause");
exit(dwError);
}
int main()
{
LPTSTR szCmdline[] = {"cmd"};
STARTUPINFOW si;
PROCESS_INFORMATION pi;
memset(&si, 0, sizeof(si));
si.cb = sizeof(si);
TCHAR un[UNLEN+1];
DWORD size = UNLEN + 1;
GetUserName(un, &size);
string una(un);
bool sys = !una.compare("SYSTEM");
if(!sys) {
system("cls");
if(!CreateProcessW(L"C:\\Windows\\System32\\cmd.exe", NULL, NULL, NULL, FALSE, NORMAL_PRIORITY_CLASS | CREATE_BREAKAWAY_FROM_JOB, NULL, NULL, &si, &pi)) ReportError(L"normal Create process");
return 0;
}
wchar_t szUserName[INFO_BUFFER_SIZE] = {};
wchar_t szPassword[INFO_BUFFER_SIZE] = {};
wchar_t *pc = NULL;
HANDLE hToken = NULL;
HANDLE aToken = NULL;
BOOL dup = FALSE;
BOOL logon = FALSE;
printf("Enter the username: ");
fgetws(szUserName, ARRAYSIZE(szUserName), stdin);
pc = wcschr(szUserName, '\n');
if (pc != NULL) *pc = '\0'; // Remove the trailing L'\n'
cout << endl;
printf("Enter the password: ");
fgetws(szPassword, ARRAYSIZE(szPassword), stdin);
pc = wcschr(szPassword, '\n');
if (pc != NULL) *pc = '\0'; // Remove the trailing L'\n'
if(!LogonUserW(szUserName, NULL, szPassword, LOGON32_LOGON_NETWORK, LOGON32_PROVIDER_DEFAULT, &hToken)) ReportError(L"Logon");
else logon = TRUE;
if(!DuplicateTokenEx(hToken, TOKEN_DUPLICATE | TOKEN_IMPERSONATE, NULL, SecurityImpersonation, TokenPrimary, &aToken)) ReportError(L"Impersonate");
else dup = TRUE;
if(!CreateProcessAsUserW(aToken,L"C:\\Windows\\System32\\cmd.exe", NULL, NULL, NULL, FALSE, CREATE_BREAKAWAY_FROM_JOB, NULL, L"C:\\Windows\\System32\\", &si, &pi)){
ReportError(L"Create Process");
}
SecureZeroMemory(szPassword, sizeof(szPassword));
}
I would like to know why sethc is not allowed CreateProcess at all if it is derived from winlogon. I am running Windows 7. The weird thing is that system(command) works fine. I use system("pause"); once.

Answer 1

While it is difficult to say what your question actually is, be aware that there is a specific privilege called PROCESS_CREATE_PROCESS.
From MSDN:
PROCESS_CREATE_PROCESS (0x0080) Required to create a process.
A process lacking this privilege can't spawn child processes. system("pause"); does not create a child process, because pause is a built-in shell command, but I understand why you might have got that impression.
So check if your process has that privilege. Use process explorer or simply a WINAPI function, there's bound to be one.
If you want to know why Microsoft developers decided not to give that privilege to sethc, you'd have to ask them.