This documentation is archived and is not being maintained.

HttpListener.UnsafeConnectionNtlmAuthentication Property

Gets or sets a Boolean value that controls whether, when NTLM is used, additional requests using the same Transmission Control Protocol (TCP) connection are required to authenticate.

Namespace:  System.Net
Assembly:  System (in System.dll)

public bool UnsafeConnectionNtlmAuthentication { get; set; }

Property Value

Type: System.Boolean
true if the IIdentity of the first request will be used for subsequent requests on the same connection; otherwise, false. The default value is false.


This object has been closed.

When this property is set to true and the first request over a particular TCP connection is authenticated using NTLM, subsequent requests over the same TCP connection are processed using the authentication information (IIdentity) of the initial request.

This property has no effect when NTLM is not the authentication protocol. When Negotiate is specified as the authentication protocol, this property has an effect only if NTLM is the actual protocol used for authentication.


While setting this property to true increases performance because the HttpListener does not send additional NTLM authentication challenges, there is a security risk in not requiring all requests to provide authentication information. You must determine whether the increase in performance is worth this risk.

The following code example demonstrates setting this property.

public static void SimpleListenerWithUnsafeAuthentication(string[] prefixes)
    // URI prefixes are required,
    // for example "".
    if (prefixes == null || prefixes.Length == 0)
      throw new ArgumentException("prefixes");
    // Set up a listener.
    HttpListener listener = new HttpListener();
    foreach (string s in prefixes)
    // Specify Negotiate as the authentication scheme.
    listener.AuthenticationSchemes = AuthenticationSchemes.Negotiate;
    // If NTLM is used, we will allow multiple requests on the same
    // connection to use the authentication information of first request.
    // This improves performance but does reduce the security of your 
    // application. 
    listener.UnsafeConnectionNtlmAuthentication = true;
    // This listener does not want to receive exceptions 
    // that occur when sending the response to the client.
    listener.IgnoreWriteExceptions = true;
    // ... process requests here.


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.