NamedPipeClientStream throws UnauthorizedAccessException on Connect

Question

I have the same problem everyone else has when connecting a "write" pipe to a running service: UnauthorizedAccessException. I tried every solution and nothing can make it connect successfully.

The scenario is having a low-integrity C#/WPF app running in system tray that gets notifications from a Windows Service using named pipes and can tell the service to cancel certain operations or wait for more data (which is why it needs a write pipe to the service). Reading from service's pipe works fine, and I am using two pipe objects (one from service to client and another from client to service).

The service runs under a domain user's account, but the pipe fails to connect no matter what it runs under, including Local System.

Server pipes are created like so:

PipeSecurity ps = new PipeSecurity();

// Production service runs under current user credentials.
ps.AddAccessRule(new PipeAccessRule(WindowsIdentity.GetCurrent().User, PipeAccessRights.ReadWrite | PipeAccessRights.CreateNewInstance, AccessControlType.Allow));

// Test service runs under local system credentials.
ps.AddAccessRule(new PipeAccessRule(new SecurityIdentifier(WellKnownSidType.LocalSystemSid, null), PipeAccessRights.ReadWrite | PipeAccessRights.CreateNewInstance, AccessControlType.Allow));

// Add world just for the hell of it, still won't work.
ps.AddAccessRule(new PipeAccessRule(new SecurityIdentifier(WellKnownSidType.WorldSid, null), PipeAccessRights.FullControl, AccessControlType.Allow));

this.readPipe = new NamedPipeServerStream(clientPipeName, PipeDirection.In);
this.writePipe = new NamedPipeServerStream(serverPipeName, PipeDirection.Out, 1, PipeTransmissionMode.Byte, PipeOptions.None, 1024, 1024, ps);

Client pipes are created like so:

this.readPipe = new NamedPipeClientStream(".", serverPipeName, PipeDirection.In);
this.writePipe = new NamedPipeClientStream(".", clientPipeName, PipeDirection.Out);

// This doesn't make a difference.
//this.writePipe = new NamedPipeClientStream(".", clientPipeName, PipeAccessRights.FullControl, PipeOptions.None, TokenImpersonationLevel.None, HandleInheritability.None);

Answer 1

Didn't want to leave this open, since this was solved and following code is in production.

• Server pipe must have ACL list carefully constructed to allow connections from low-integrity client pipes, as long as users are authenticated or administrators. See CreateNativePipeSecurity().

• Client pipe is created as usual

  /// <summary>
  /// Creates the client and server pipes.
  /// </summary>
  private void CreatePipes()
  {
      string serverPipeName = string.Format("{0}server", this.pipeName);
      string clientPipeName = string.Format("{0}client", this.pipeName);
  
      if (this.readPipe != null)
      {
          this.readPipe.Dispose();
      }
  
      if (this.writePipe != null)
      {
          this.writePipe.Dispose();
      }
  
      if (this.server)
      {
          // Create a write pipe for sending notifications to client.
          this.writePipe = new NamedPipeServerStream(clientPipeName, PipeDirection.Out);
  
          // Create a read pipe for receiving notifications from the client.
          // Creating a pipe to high integrity process from low integrity process requires native access list creation (.NET bug).
          NativeMethods.SECURITY_ATTRIBUTES securityAttributes = this.CreateNativePipeSecurity();
          IntPtr securityAttributesPtr = Marshal.AllocHGlobal(Marshal.SizeOf(securityAttributes));
          Marshal.StructureToPtr(securityAttributes, securityAttributesPtr, false);
  
          string nativePipeName = string.Format(@"\\.\pipe\{0}", serverPipeName);
  
          SafePipeHandle nativePipe = NativeMethods.CreateNamedPipe(
              nativePipeName,
              NativeMethods.PipeOpenMode.PIPE_ACCESS_INBOUND,
              0,
              NativeMethods.PipeInstances.PIPE_UNLIMITED_INSTANCES,
              0,
              0,
              NativeMethods.PipeWait.NMPWAIT_WAIT_FOREVER,
              securityAttributesPtr);
  
          int error = Marshal.GetLastWin32Error();
  
          Marshal.FreeHGlobal(securityAttributesPtr);
  
          if (nativePipe.IsInvalid)
          {                    
              throw new Win32Exception(error);
          }
  
          this.readPipe = new NamedPipeServerStream(PipeDirection.In, false, false, nativePipe);
      }
      else
      {
          // Create a read pipe for receiving notifications from server.
          this.readPipe = new NamedPipeClientStream(".", clientPipeName, PipeDirection.In);
  
          // Create a write pipe for sending notifications to the server.
          this.writePipe = new NamedPipeClientStream(".", serverPipeName, PipeDirection.Out);
      }
  }
  
  /// <summary>
  /// Generate security attributes to allow low integrity process to connect to high integrity service.
  /// </summary>
  /// <returns>A structure filled with proper attributes.</returns>
  private NativeMethods.SECURITY_ATTRIBUTES CreateNativePipeSecurity()
  {
      // Define the SDDL for the security descriptor.
      string sddl = "D:" +        // Discretionary ACL
          "(A;OICI;GRGW;;;AU)" +  // Allow read/write to authenticated users
          "(A;OICI;GA;;;BA)";     // Allow full control to administrators
  
      IntPtr securityDescriptor = IntPtr.Zero;
  
      if (NativeMethods.ConvertStringSecurityDescriptorToSecurityDescriptor(
          sddl, 1, out securityDescriptor, IntPtr.Zero) == 0)
      {
          throw new Win32Exception(Marshal.GetLastWin32Error());
      }
  
      NativeMethods.SECURITY_ATTRIBUTES sa = new NativeMethods.SECURITY_ATTRIBUTES();
      sa.nLength = Marshal.SizeOf(sa);
      sa.lpSecurityDescriptor = securityDescriptor;
      sa.bInheritHandle = 0;
  
      return sa;
  }