Added signature verification support for SMB2 client

SMBLibrary.Tests/Client/SMB2SigningTests.cs

@@ -0,0 +1,264 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using SMBLibrary.Client;
+using System;
+using System.Net;
+using SMBLibrary.Server;
+using SMBLibrary.Authentication.GSSAPI;
+using SMBLibrary.Client.Authentication;
+using System.Collections.Generic;
+using System.Net.Sockets;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace SMBLibrary.Tests.Client
+{
+    [TestClass]
+    public class SMB2SigningTests
+    {
+        private TcpRelay m_tcpRelay;
+        private SMBServer m_smbServer;
+        private SMB2Client client;
+        private static readonly byte[] m_sessionKey = new byte[16];
+        private static readonly byte[] m_fakeIdentifier = new byte[] { 1, 2, 3, 4, 5, 6 };
+
+        [TestInitialize]
+        public void Initialize()
+        {
+            new Random().NextBytes(m_sessionKey);
+
+            SMBShareCollection shares = new SMBShareCollection();
+            GSSProvider securityProvider = new GSSProvider(new FakeAuthenticationProvider());
+            m_smbServer = new SMBServer(shares, securityProvider);
+            m_smbServer.Start(IPAddress.Any, SMBTransportType.NetBiosOverTCP, 30002, false, true, true, null);
+
+            m_tcpRelay = new TcpRelay();
+            Task.Run(m_tcpRelay.Start);
+
+            client = new SMB2Client();
+            client.SigningRequired = true;
+            m_tcpRelay.SignatureManipulationEnabled = true;
+            Assert.IsTrue(client.Connect(IPAddress.Loopback, SMBTransportType.DirectTCPTransport, 30001, 3000));
+        }
+
+        [TestCleanup]
+        public void CleanUp()
+        {
+            client?.Disconnect();
+            m_tcpRelay.Stop();
+            m_smbServer.Stop();
+        }
+
+        [TestMethod]
+        public void When_SignatureIsValid_ShouldNotBeInvalid()
+        {
+            client.DisconnectOnInvalidSignature = false;
+            m_tcpRelay.SignatureManipulationEnabled = false;
+
+            Assert.AreEqual(NTStatus.STATUS_SUCCESS, client.Login(new FakeAuthenticationClient()));
+
+            client.TreeConnect("test", out NTStatus status);
+            Assert.AreEqual(NTStatus.STATUS_OBJECT_PATH_NOT_FOUND, status);
+            Assert.IsTrue(client.IsConnected);
+        }
+
+        [TestMethod]
+        public void When_SigningEnabledAndSignatureIsInvalid_LoginShouldFail()
+        {
+            client.DisconnectOnInvalidSignature = false;
+            m_tcpRelay.SignatureManipulationEnabled = true;
+
+            Assert.AreEqual(NTStatus.STATUS_INVALID_SMB, client.Login(new FakeAuthenticationClient()));
+            Assert.IsTrue(client.IsConnected);
+        }
+
+        [TestMethod]
+        public void When_SigningEnabledAndSignatureIsInvalid_LoginShouldDisconnect()
+        {
+            client.DisconnectOnInvalidSignature = true;
+            m_tcpRelay.SignatureManipulationEnabled = true;
+
+            Assert.AreEqual(NTStatus.STATUS_INVALID_SMB, client.Login(new FakeAuthenticationClient()));
+            Assert.IsFalse(client.IsConnected);
+        }
+
+        [TestMethod]
+        public void When_SigningEnabledAndSignatureIsInvalid_CommandShouldFail()
+        {
+            m_tcpRelay.SignatureManipulationEnabled = false;
+            client.DisconnectOnInvalidSignature = false;
+
+            Assert.AreEqual(NTStatus.STATUS_SUCCESS, client.Login(new FakeAuthenticationClient()));
+
+            m_tcpRelay.SignatureManipulationEnabled = true;
+
+            client.TreeConnect("test", out NTStatus status);
+            Assert.AreEqual(NTStatus.STATUS_INVALID_SMB, status);
+            Assert.IsTrue(client.IsConnected);
+        }
+
+        [TestMethod]
+        public void When_SigningEnabledAndSignatureIsInvalid_CommandShouldDisconnect()
+        {
+            m_tcpRelay.SignatureManipulationEnabled = false;
+            client.DisconnectOnInvalidSignature = true;
+
+            Assert.AreEqual(NTStatus.STATUS_SUCCESS, client.Login(new FakeAuthenticationClient()));
+
+            m_tcpRelay.SignatureManipulationEnabled = true;
+
+            client.TreeConnect("test", out NTStatus status);
+            Assert.AreEqual(NTStatus.STATUS_INVALID_SMB, status);
+            Assert.IsFalse(client.IsConnected);
+        }
+
+        private class FakeAuthenticationClient : IAuthenticationClient
+        {
+            public byte[] GetSessionKey()
+            {
+                return m_sessionKey;
+            }
+
+            public byte[] InitializeSecurityContext(byte[] securityBlob)
+            {
+                SimpleProtectedNegotiationTokenInit initToken = new SimpleProtectedNegotiationTokenInit();
+                initToken.MechanismTypeList = new List<byte[]>() { m_fakeIdentifier };
+                return initToken.GetBytes(true);
+            }
+        }
+
+        private class FakeAuthenticationProvider : IGSSMechanism
+        {
+            public byte[] Identifier => m_fakeIdentifier;
+
+            public NTStatus AcceptSecurityContext(ref object context, byte[] inputToken, out byte[] outputToken)
+            {
+                outputToken = null;
+                return NTStatus.STATUS_SUCCESS;
+            }
+
+            public bool DeleteSecurityContext(ref object context)
+            {
+                return true;
+            }
+
+            public object GetContextAttribute(object context, GSSAttributeName attributeName)
+            {
+                switch (attributeName)
+                {
+                    case GSSAttributeName.SessionKey:
+                        return m_sessionKey;
+                }
+                return null;
+            }
+        }
+
+        private class TcpRelay
+        {
+            private TcpListener m_relay;
+            private TcpClient m_localClient;
+            private TcpClient m_remoteClient;
+            private Thread m_clientToServer;
+            private Thread m_serverToClient;
+
+            public bool SignatureManipulationEnabled { get; set; } = false;
+
+            public void Start()
+            {
+                m_remoteClient = new TcpClient();
+                m_remoteClient.Connect(IPAddress.Loopback, 30002);
+
+                m_relay = new TcpListener(IPAddress.Any, 30001);
+                m_relay.Start();
+
+                m_localClient = m_relay.AcceptTcpClient();
+
+                NetworkStream localStream = m_localClient.GetStream();
+                NetworkStream remoteStream = m_remoteClient.GetStream();
+
+                m_clientToServer = new Thread(() => ForwardData(localStream, remoteStream));
+                m_serverToClient = new Thread(() => ForwardData(remoteStream, localStream));
+
+                m_clientToServer.Start();
+                m_serverToClient.Start();
+            }
+
+            public void Stop()
+            {
+                m_localClient?.Dispose();
+                m_remoteClient?.Dispose();
+                m_relay?.Stop();
+                m_clientToServer.Join();
+                m_serverToClient.Join();
+            }
+
+            private void ForwardData(NetworkStream input, NetworkStream output)
+            {
+                byte[] buffer = new byte[4096];
+                int bytesRead;
+
+                try
+                {
+                    while ((bytesRead = input.Read(buffer, 0, buffer.Length)) > 0)
+                    {
+                        if (TryGetSmb2HeaderOffset(buffer, bytesRead, out int smbOffset) && IsSigned(buffer, smbOffset) && SignatureManipulationEnabled)
+                        {
+                            ManipulateSignature(buffer, smbOffset);
+                        }
+
+                        output.Write(buffer, 0, bytesRead);
+                    }
+                }
+                catch
+                {
+                    // Likely disconnected
+                }
+            }
+
+            private static bool TryGetSmb2HeaderOffset(byte[] data, int length, out int offset)
+            {
+                offset = -1;
+
+                // NetBIOS Session Header?
+                if (length >= 68 && data[0] == 0x00)
+                {
+                    if (data[4] == 0xFE && data[5] == (byte)'S' && data[6] == (byte)'M' && data[7] == (byte)'B')
+                    {
+                        offset = 4;
+                        return true;
+                    }
+                }
+                else if (length >= 64 && data[0] == 0xFE && data[1] == (byte)'S' && data[2] == (byte)'M' && data[3] == (byte)'B')
+                {
+                    offset = 0;
+                    return true;
+                }
+
+                return false;
+            }
+
+            private static bool IsSigned(byte[] data, int offset)
+            {
+                uint flags = BitConverter.ToUInt32(data, offset + 16);
+                return (flags & 0x00000008) != 0;
+            }
+
+            private static void ManipulateSignature(byte[] data, int offset)
+            {
+                Random rand = new Random();
+
+                // Change a random signature byte
+                int idx = rand.Next(48, 48 + 16);
+
+                // Generate a new random byte and make sure it is different from the current value
+                int byteValue;
+                do
+                {
+                    byteValue = rand.Next(0, 256);
+                }
+                while (data[offset + idx] == byteValue);
+
+                data[offset + idx] = (byte) byteValue;
+            }
+        }
+    }
+}

SMBLibrary/Client/SMB2Client.cs

@@ -1,5 +1,5 @@
 /* Copyright (C) 2017-2025 Tal Aloni <tal.aloni.il@gmail.com>. All rights reserved.
- * 
+ *
  * You can redistribute this program and/or modify it under the terms of
  * the GNU Lesser Public License as published by the Free Software Foundation,
  * either version 3 of the License, or (at your option) any later version.
@@ -59,10 +59,15 @@ namespace SMBLibrary.Client
         private byte[] m_preauthIntegrityHashValue; // SMB 3.1.1
         private ushort m_availableCredits = 1;
 
+        private byte[] m_sessionSetupResponseMessage;
+
         public SMB2Client()
         {
         }
 
+        public bool SigningRequired { get; set; } = false;
+        public bool DisconnectOnInvalidSignature { get; set; } = false;
+
         /// <param name="serverName">
         /// When a Windows Server host is using Failover Cluster and Cluster Shared Volumes, each of those CSV file shares is associated
         /// with a specific host name associated with the cluster and is not accessible using the node IP address or node host name.
@@ -197,7 +202,7 @@ namespace SMBLibrary.Client
         private bool NegotiateDialect()
         {
             NegotiateRequest request = new NegotiateRequest();
-            request.SecurityMode = SecurityMode.SigningEnabled;
+            request.SecurityMode = SigningRequired ? SecurityMode.SigningRequired | SecurityMode.SigningEnabled : SecurityMode.SigningEnabled;
             request.Capabilities = Capabilities.Encryption;
             request.ClientGuid = Guid.NewGuid();
             request.ClientStartTime = DateTime.Now;
@@ -219,7 +224,7 @@ namespace SMBLibrary.Client
                 m_dialect = response.DialectRevision;
                 // [MS-SMB2] 3.3.5.7 If Connection.Dialect is "3.1.1" and Session.IsAnonymous and Session.IsGuest
                 // are set to FALSE and the request is not signed or not encrypted, then the server MUST disconnect the connection.
-                m_signingRequired = (response.SecurityMode & SecurityMode.SigningRequired) > 0 ||
+                m_signingRequired = SigningRequired || (response.SecurityMode & SecurityMode.SigningRequired) > 0 ||
                                     response.DialectRevision == SMB2Dialect.SMB311;
                 m_maxTransactSize = Math.Min(response.MaxTransactSize, ClientMaxTransactSize);
                 m_maxReadSize = Math.Min(response.MaxReadSize, ClientMaxReadSize);
@@ -256,7 +261,7 @@ namespace SMBLibrary.Client
             }
 
             SessionSetupRequest request = new SessionSetupRequest();
-            request.SecurityMode = SecurityMode.SigningEnabled;
+            request.SecurityMode = SigningRequired ? SecurityMode.SigningRequired | SecurityMode.SigningEnabled : SecurityMode.SigningEnabled;
             request.SecurityBuffer = negotiateMessage;
             TrySendCommand(request);
             SMB2Command response = WaitForCommand(request.MessageID);
@@ -270,7 +275,7 @@ namespace SMBLibrary.Client
 
                 m_sessionID = response.Header.SessionID;
                 request = new SessionSetupRequest();
-                request.SecurityMode = SecurityMode.SigningEnabled;
+                request.SecurityMode = SigningRequired ? SecurityMode.SigningRequired | SecurityMode.SigningEnabled : SecurityMode.SigningEnabled;
                 request.SecurityBuffer = authenticateMessage;
                 TrySendCommand(request);
                 response = WaitForCommand(request.MessageID);
@@ -301,6 +306,26 @@ namespace SMBLibrary.Client
                         m_encryptionKey = SMB2Cryptography.GenerateClientEncryptionKey(m_sessionKey, m_dialect, m_preauthIntegrityHashValue);
                         m_decryptionKey = SMB2Cryptography.GenerateClientDecryptionKey(m_sessionKey, m_dialect, m_preauthIntegrityHashValue);
                     }
+
+                    // [MS-SMB2] 3.2.5.1.3 Verifying the Signature
+                    // If signature verification fails, the client MUST discard the received message.
+                    // The client MAY also choose to disconnect the connection.
+                    try
+                    {
+                        if (!VerifySignature(m_sessionSetupResponseMessage, response))
+                        {
+                            m_isLoggedIn = false;
+                            if (DisconnectOnInvalidSignature)
+                            {
+                                Disconnect();
+                            }
+                            return NTStatus.STATUS_INVALID_SMB;
+                        }
+                    }
+                    finally
+                    {
+                        m_sessionSetupResponseMessage = null;
+                    }
                 }
                 return response.Header.Status;
             }
@@ -526,14 +551,42 @@ namespace SMBLibrary.Client
                 // and the client MUST NOT attempt to locate the request, but instead process it as follows:
                 // If the command field in the SMB2 header is SMB2 OPLOCK_BREAK, it MUST be processed as specified in 3.2.5.19.
                 // Otherwise, the response MUST be discarded as invalid.
-                if (command.Header.MessageID != 0xFFFFFFFFFFFFFFFF || command.Header.Command == SMB2CommandName.OplockBreak)
+                if (command.Header.MessageID == 0xFFFFFFFFFFFFFFFF && command.Header.Command != SMB2CommandName.OplockBreak)
                 {
-                    lock (m_incomingQueueLock)
+                    return;
+                }
+
+                // [MS-SMB2] 3.2.5.1.3 Verifying the Signature
+                // If signature verification fails, the client MUST discard the received message.
+                // The client MAY also choose to disconnect the connection.
+                if (m_isLoggedIn)
+                {
+                    // This check covers all messages except the final session setup message which is treated seperately
+                    if (!VerifySignature(messageBytes, command))
                     {
-                        m_incomingQueue.Add(command);
-                        m_incomingQueueEventHandle.Set();
+                        if (DisconnectOnInvalidSignature)
+                        {
+                            m_isLoggedIn = false;
+                            Disconnect();
+                        }
+                        return;
                     }
                 }
+                else if ((command.Header.Command == SMB2CommandName.SessionSetup) &&
+                            (command.Header.Status == NTStatus.STATUS_SUCCESS))
+                {
+                    // The final session setup message already has a valid signature, but the session/signing key have not been set yet (m_isLoggedIn is false).
+                    // The message is evaluated within the Login() method, which will then determine the keys and set m_isLoggedIn to true.
+                    // Nevertheless, the signature must be verified. So the raw message is preserved here and the signature is verified later in the
+                    // Login() method, after the keys have been set.
+                    m_sessionSetupResponseMessage = messageBytes;
+                }
+
+                lock (m_incomingQueueLock)
+                {
+                    m_incomingQueue.Add(command);
+                    m_incomingQueueEventHandle.Set();
+                }
             }
             else if ((packet is PositiveSessionResponsePacket || packet is NegativeSessionResponsePacket) && m_transport == SMBTransportType.NetBiosOverTCP)
             {
@@ -552,6 +605,38 @@ namespace SMBLibrary.Client
             }
         }
 
+        // [MS-SMB2] 3.2.5.1.3 Verifying the Signature
+        private bool VerifySignature(byte[] messageBytes, SMB2Command command)
+        {
+            if (!m_signingRequired)
+            {
+                // Client and server require no signing at all
+                return true;
+            }
+
+            if (messageBytes == null)
+            {
+                throw new ArgumentNullException("messageBytes");
+            }
+
+            bool isUnspecifiedMessageId = command.Header.MessageID == 0xFFFFFFFFFFFFFFFF;
+            bool isPendingMessage = command.Header.Status == NTStatus.STATUS_PENDING;
+
+            if (m_encryptSessionData || isUnspecifiedMessageId || isPendingMessage)
+            {
+                // Signing is not required
+                return true;
+            }
+
+            byte[] key = (m_dialect >= SMB2Dialect.SMB300) ? m_signingKey : m_sessionKey;
+
+            Array.Clear(messageBytes, SMB2Header.SignatureOffset, command.Header.Signature.Length);
+            byte[] signature = SMB2Cryptography.CalculateSignature(key, m_dialect, messageBytes, 0, messageBytes.Length);
+            signature = ByteReader.ReadBytes(signature, 0, command.Header.Signature.Length);
+
+            return ByteUtils.AreByteArraysEqual(signature, command.Header.Signature);
+        }
+
         internal SMB2Command WaitForCommand(ulong messageID)
         {
             return WaitForCommand(messageID, out bool _);