When using the Win32 GetAppliedGPOList in C, the GPO list pointer is always NULL even when trying multiple GUIDs and even when the API returns success.

Madden, John 0

In the code below, pGPOList (the GPO list) is always NULL even when the GetAppliedGPOList returns success. I have tried multiple group policy extension GUIDs, but no luck. What am I doing wrong? This also happens when I try GetAppliedGPOList with user policies, although the code is slightly different.

static DWORD DisplayAppliedMachinePolicies()

{

PGROUP_POLICY_OBJECT  pGPOList = NULL;

LPGROUPPOLICYOBJECT pGPO = NULL;

UUID guid;

DWORD dwError = 0;

//{17D89FEC-5C44-4972-B12D-241CAEF74509}

//{3A0DBA37-F8B2-4356-83DE-3E90BD5C261F}

//{E47248BA-94CC-49c4-BBB5-9EB7F05183D0}

if (string_to_guid(L"E47248BA-94CC-49c4-BBB5-9EB7F05183D0", &guid) != 0)

{

    return ERROR_BAD_FORMAT;

}

dwError = GetAppliedGPOList(GPO_LIST_FLAG_MACHINE, NULL, NULL, &guid, &pGPOList);

if (dwError == ERROR_SUCCESS)

{

    PGROUP_POLICY_OBJECT pGPO = (PGROUP_POLICY_OBJECT)pGPOList;

    while (pGPO != NULL)

    {

        //Display properties of each GPO

        DisplayPolicyInfo((PGROUP_POLICY_OBJECT)&pGPOList);

        pGPO = pGPO->pNext;

    }

    FreeGPOList((PGROUP_POLICY_OBJECT)pGPOList);

}



return dwError;

}

Viorel 114.7K Reputation points

2024-07-24T13:51:01.5566667+00:00

Did you also obtain ERROR_SUCCESS with any random GUID?
Xiaopo Yang - MSFT 12,231 Reputation points Microsoft Vendor

2024-07-25T01:25:53.5433333+00:00

The GetAppliedGPOList is looked under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\History\{GuidExtension} key. Refer to https://stackoverflow.com/questions/46305094/getappliedgpolist-and-pguidextension-value.
Madden, John 0 Reputation points

2024-07-25T12:53:17.7266667+00:00

So I always get ERROR_SUCCESS, but the GUIDS I have tried under the reg key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Group Policy\History{GuidExtension} have not yielded any non-null pointers for pGPOList yet. Perhaps I have tried the wrong ones - I will loop through all of them to test.

Thanks for the input!

1 answer

Castorix31 83,201

I did a loop on keys at "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\GPExtensions"(RegOpenKeyEx/RegEnumKey)

and I got some != NULL

(

{35378EAC-683F-11D2-A89A-00C04FBBCFA2}

{F312195E-3D9D-447A-A3F5-08DFFA24735E}

on my PC)

Madden, John 0 Reputation points

2024-07-25T12:54:14.11+00:00

I'll try those GUIDs and see if they work - thanks! I will also look through the list of available GUIDs as well.

Castorix31 83,201

This is the quick test I did (I have put a BP on the line

FreeGPOList(pGPOList);

to check not NULL pGPOList)

{
					LONG nResult;
					DWORD nKeyIdx = 0;
					WCHAR wsRegBuffer[MAX_PATH + 1] = L"";
					HKEY hKey = NULL;				
					BOOL(FAR STDAPICALLTYPE* pGUIDFromString)(LPCTSTR psz, LPGUID pguid) = NULL;
					HMODULE hInstance = LoadLibrary(L"Shell32.dll");
					if (hInstance)
					{
						(FARPROC&)pGUIDFromString = GetProcAddress(hInstance, (LPCSTR)MAKEINTRESOURCE(704));
						FreeModule(hInstance);
					}
					if (RegOpenKeyEx(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Winlogon\\GPExtensions", 0, KEY_READ | KEY_WOW64_64KEY, &hKey) == ERROR_SUCCESS)
					{
						while (TRUE)
						{
							nResult = RegEnumKey(hKey, nKeyIdx, wsRegBuffer, ARRAYSIZE(wsRegBuffer));
							if (nResult == ERROR_NO_MORE_ITEMS)
							{
								break;
							}
							else
							{
								PGROUP_POLICY_OBJECT pGPOList = NULL;
								GUID guid;
								BOOL bRet = pGUIDFromString(wsRegBuffer, &guid);
								// pGPOList != NULL 
								// {35378EAC-683F-11D2-A89A-00C04FBBCFA2}
								// {F312195E-3D9D-447A-A3F5-08DFFA24735E}
								DWORD nError = GetAppliedGPOList(GPO_LIST_FLAG_MACHINE, NULL, NULL, &guid, &pGPOList);
								if (nError == ERROR_SUCCESS && pGPOList != NULL)
								{
									// Code...
									FreeGPOList(pGPOList);
								}								
							}
							++nKeyIdx;
						}
						RegCloseKey(hKey);
					}					
}

Madden, John 0 Reputation points

2024-07-25T17:13:13.44+00:00

Thanks Castorix31, that was very helpful. I will add that to my code. I've finally been able to look at the GPO's from the list and print out their information. When I am done I will post the code.

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When using the Win32 GetAppliedGPOList in C, the GPO list pointer is always NULL even when trying multiple GUIDs and even when the API returns success.

1 answer