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; }