diff --git a/SMBLibrary/Enums/NTStatus.cs b/SMBLibrary/Enums/NTStatus.cs
index 9ce465e..0a544ed 100644
--- a/SMBLibrary/Enums/NTStatus.cs
+++ b/SMBLibrary/Enums/NTStatus.cs
@@ -54,6 +54,7 @@ namespace SMBLibrary
         STATUS_BAD_DEVICE_TYPE = 0xC00000CB,
         STATUS_BAD_NETWORK_NAME = 0xC00000CC,
         STATUS_TOO_MANY_SESSIONS = 0xC00000CE,
+        STATUS_REQUEST_NOT_ACCEPTED = 0xC00000D0,
         STATUS_DIRECTORY_NOT_EMPTY = 0xC0000101,
         STATUS_NOT_A_DIRECTORY = 0xC0000103,
         STATUS_TOO_MANY_OPENED_FILES = 0xC000011F,
diff --git a/SMBLibrary/Server/SMB2/SessionSetupHelper.cs b/SMBLibrary/Server/SMB2/SessionSetupHelper.cs
index 556f221..902a8c5 100644
--- a/SMBLibrary/Server/SMB2/SessionSetupHelper.cs
+++ b/SMBLibrary/Server/SMB2/SessionSetupHelper.cs
@@ -1,4 +1,4 @@
-/* Copyright (C) 2017-2020 Tal Aloni <tal.aloni.il@gmail.com>. All rights reserved.
+/* Copyright (C) 2017-2022 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,
@@ -51,6 +51,11 @@ namespace SMBLibrary.Server.SMB2
                 sessionID = allocatedSessionID.Value;
                 response.Header.SessionID = allocatedSessionID.Value;
             }
+            else if (state.GetSession(sessionID) != null)
+            {
+                // We already have an established session associated with this sessionID, the client is in violation
+                return new ErrorResponse(request.CommandName, NTStatus.STATUS_REQUEST_NOT_ACCEPTED);
+            }
 
             if (status == NTStatus.SEC_I_CONTINUE_NEEDED)
             {