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HttpRequestValidationException Class

The exception that is thrown when a potentially malicious input string is received from the client as part of the request data. This class cannot be inherited.


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

public sealed class HttpRequestValidationException : HttpException

The HttpRequestValidationException type exposes the following members.

Public methodHttpRequestValidationException()Creates a new instance of the HttpRequestValidationException class.
Public methodHttpRequestValidationException(String)Creates a new HttpRequestValidationException exception with the specified error message.
Public methodHttpRequestValidationException(String, Exception)Initializes a new instance of the HttpRequestValidationException class with a specified error message and a reference to the inner exception that is the cause of the exception.

Public propertyDataGets a collection of key/value pairs that provide additional user-defined information about the exception. (Inherited from Exception.)
Public propertyErrorCodeGets the HRESULT of the error. (Inherited from ExternalException.)
Public propertyHelpLinkGets or sets a link to the help file associated with this exception. (Inherited from Exception.)
Protected propertyHResultGets or sets HRESULT, a coded numerical value that is assigned to a specific exception. (Inherited from Exception.)
Public propertyInnerExceptionGets the Exception instance that caused the current exception. (Inherited from Exception.)
Public propertyMessageGets a message that describes the current exception. (Inherited from Exception.)
Public propertySourceGets or sets the name of the application or the object that causes the error. (Inherited from Exception.)
Public propertyStackTraceGets a string representation of the immediate frames on the call stack. (Inherited from Exception.)
Public propertyTargetSiteGets the method that throws the current exception. (Inherited from Exception.)
Public propertyWebEventCodeGets the event codes that are associated with the HTTP exception. (Inherited from HttpException.)

Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetBaseExceptionWhen overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. (Inherited from Exception.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetHtmlErrorMessageGets the HTML error message to return to the client. (Inherited from HttpException.)
Public methodGetHttpCodeGets the HTTP response status code to return to the client. (Inherited from HttpException.)
Public methodGetObjectDataGets information about the exception and adds it to the SerializationInfo object. (Inherited from HttpException.)
Public methodGetTypeGets the runtime type of the current instance. (Inherited from Exception.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that contains the HRESULT of the error. (Inherited from ExternalException.)

Protected eventSerializeObjectStateOccurs when an exception is serialized to create an exception state object that contains serialized data about the exception. (Inherited from Exception.)

Constraining and validating user input is essential in a Web application to prevent hacker attacks that rely on malicious input strings. Cross-site scripting attacks are one example of such hacks. Other types of malicious or undesired data can be passed in a request through various forms of input. By limiting the kinds of data that is passed at a low level in an application, you can prevent undesirable events, even when programmers who are using your code do not put the proper validation techniques in place.

Request validation detects potentially malicious client input and throws this exception to abort processing of the request. A request abort can indicate an attempt to compromise the security of your application, such as a cross-site scripting attack. It is strongly recommended that your application explicitly check all input regarding request aborts. However, you can disable request validation by setting the validateRequest attribute in the @ Page directive to false, as shown in the following example:

<%@ Page validateRequest="false" %>

To disable request validation for your application, you must modify or create a Web.config file for your application and set the validateRequest attribute of the pages section to false, as shown in the following example:

    <pages validateRequest="false" /> 

To disable request validation for all applications on your server, you can make this modification to the Machine.config file.


It is strongly recommended that your application explicitly check all inputs it uses in addition to the request validation performed by ASP.NET. The request validation feature cannot catch all attacks, especially those crafted specifically against your application logic.

The following code example demonstrates how to check for malicious user input by using an HttpRequestValidationException.

Security noteSecurity Note

This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview.

<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<script runat="server">
    void Button1_Click(object sender, EventArgs e)
        Label1.Text = txt1.Text;

<html xmlns="" >
<head id="Head1" runat="server">
    <title>Untitled Page</title>
    <form id="form1" runat="server">
        <asp:TextBox id="txt1" Runat="server" />
        <asp:Button ID="Button1" Runat="server" Text="Button" OnClick="Button1_Click" />
        <br /><br />You entered: <asp:Label ID="Label1" Runat="server" Text="Label" />.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1

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.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.