Create nonelevated process from elevated process with CreateProcessAsUser function - c++

Question

I am running a program with SYSTEM privleges. I ask for the usename and password for a handle from LogonUser(szUserName, NULL, szPassword, LOGON32_LOGON_NETWORK, LOGON32_PROVIDER_DEFAULT, &hToken) for a local logon. I want to run the cmd.exe program as the user credentials provided from the logon. The logon is successful, but when I try to run the process, nothing happens. The program aborts. My code 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);
}
int main()
{
TCHAR un[UNLEN+1];
DWORD size = UNLEN + 1;
GetUserName(un, &size);
string una(un);
bool sys = !una.compare("SYSTEM");
if(!sys) {
system("cls");
system("title Command Prompt");
system("cmd");
return 0;
}
char szUserName[INFO_BUFFER_SIZE] = {};
char szPassword[INFO_BUFFER_SIZE] = {};
char *pc = NULL;
HANDLE hToken = NULL;
BOOL fSucceeded = FALSE;
BOOL logon = FALSE;
printf("Enter the username: ");
fgets(szUserName, ARRAYSIZE(szUserName), stdin);
pc = strchr(szUserName, '\n');
if (pc != NULL) *pc = '\0'; // Remove the trailing L'\n'
cout << endl;
//string un(szUserName);
printf("Enter the password: ");
fgets(szPassword, ARRAYSIZE(szPassword), stdin);
pc = strchr(szPassword, '\n');
if (pc != NULL) *pc = '\0'; // Remove the trailing L'\n'
if (!LogonUser(szUserName, NULL, szPassword, LOGON32_LOGON_NETWORK, LOGON32_PROVIDER_DEFAULT, &hToken))
{
ReportError(L"Logon");
goto Cleanup;
}
else logon = true;
// Impersonate the logged on user.
if (!ImpersonateLoggedOnUser(hToken))
{
ReportError(L"imp");
goto Cleanup;
}
fSucceeded = true;
Cleanup:
// Clean up the buffer containing sensitive password.
SecureZeroMemory(szPassword, sizeof(szPassword));
LPTSTR szCmdline[] = {"C:\\windows\\system32\\cmd.exe"};
STARTUPINFO si;
PROCESS_INFORMATION pi;
TCHAR uni[UNLEN+1];
DWORD sizei = UNLEN + 1;
GetUserName(uni, &sizei);
string unai(uni);
cout << unai << endl;
memset(&si, 0, sizeof(si));
si.cb = sizeof(si);
HANDLE phToken = NULL;
BOOL dup = FALSE;
if(!DuplicateTokenEx(hToken, TOKEN_DUPLICATE | TOKEN_IMPERSONATE, NULL, SecurityImpersonation, TokenImpersonation, &phToken)){
ReportError(L"DUPLICATE TOKEN");
}
else dup = TRUE;
system("pause");
// If the impersonation was successful, undo the impersonation.
if (fSucceeded && logon && dup)
{
system("cls");
system("title Command Prompt");
//system("cmd");
if(!CreateProcessAsUser(
phToken, // client's access token
NULL, // file to execute
*szCmdline, // command line
NULL, // pointer to process SECURITY_ATTRIBUTES
NULL, // pointer to thread SECURITY_ATTRIBUTES
FALSE, // handles are not inheritable
NORMAL_PRIORITY_CLASS, // creation flags
NULL, // pointer to new environment block
NULL, // name of current directory
&si, // pointer to STARTUPINFO structure
&pi // receives information about new process
)){
ReportError(L"Create Process");
}
if (!RevertToSelf())
{
ReportError(L"Undo Imp");
}
}
system("pause");
}
I really would like the nonelevated proccess to avoid security issues.
Please don't tell me that my typed password is shown. I know that and will fix that later.

Answer 1

Try using the CreateProcessWithLogonUser Function. This should do that all for you with no errors.

Answer 2

You're not initializing si. You need to do this before calling CreateProcessAsUser:
memset(&si, 0, sizeof(si));
si.cb = sizeof(si);