How do I add a CAPTCHA to a web site written with ASP.NET/VB

Robert Barnes 96

A bot seems to be using my web site to send out emails via AmazonSES. I want to add a CAPTCHA to it to prevent this. I came across

https://stackoverflow.com/questions/71515717/how-to-add-captcha-in-asp-net-project

which appears to be what I want, but the examples use C# rather than VB. I tried to convert the C# to VB, but I got into a mess.

I checked the similar questions through this forum and found this

https://learn.microsoft.com/en-us/answers/questions/652050/vb-human-verificaion-boot-attacks-recaptcha-or-sim

which tells me that reCAPTCHA is not supported on this forum. So is there something that works with ASP/NET (VB)?

Any useful information will be appreciated.

Thank you, Robert.

1 answer

Lan Huang-MSFT 30,086 Reputation points Microsoft Vendor

2024-04-29T03:45:15.3233333+00:00
Hi @Robert Barnes,

You can use the MSCaptcha Library in ASP.Net.

Download MSCaptcha

In order to use MSCaptcha control, you will need to add reference of MSCaptcha Library and then register on the Page as shown below.

<%@ Register Assembly="MSCaptcha" Namespace="MSCaptcha" TagPrefix="cc1" %>

Web.Config Modifications:

<configuration> //ADD <appSettings> <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" /> </appSettings> <system.web> <compilation debug="true" strict="false" explicit="true" targetFramework="4.8" /> //ADD <httpHandlers> <add verb="GET" path="CaptchaImage.axd" type="MSCaptcha.CaptchaImageHandler, MSCaptcha"/> </httpHandlers> <httpRuntime targetFramework="4.8" /> </system.web> <system.codedom> <compilers> <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701" /> <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+" /> </compilers> </system.codedom> //ADD <system.webServer> <validation validateIntegratedModeConfiguration="false"/> <handlers> <add name="MSCaptcha.captchaImageHandler" verb="GET" path="CaptchaImage.axd" type="MSCaptcha.CaptchaImageHandler, MSCaptcha" resourceType="Unspecified"/> </handlers> </system.webServer> </configuration>

Demo

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %> <%@ Register Assembly="MSCaptcha" Namespace="MSCaptcha" TagPrefix="cc1" %> <!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> </head> <body> <form id="form1" runat="server"> <div> <cc1:CaptchaControl ID="captcha1" runat="server" CaptchaBackgroundNoise="Low" CaptchaLength="5" CaptchaHeight="60" CaptchaWidth="200" CaptchaLineNoise="None" CaptchaMinTimeout="5" CaptchaMaxTimeout="240" FontColor="#529E00" ErrorInputTooFast="Image text was typed too quickly. " ErrorInputTooSlow="Image text was typed too slowly." EnableViewState="False" /> <asp:TextBox ID="txtCaptcha" runat="server"></asp:TextBox> <asp:RequiredFieldValidator ID="rfvCaptcha" runat="server" ErrorMessage="*Required" ControlToValidate="txtCaptcha" Display="Dynamic"></asp:RequiredFieldValidator> <asp:Label ID="lblMessage" runat="server"></asp:Label> <br /> <br /> <asp:Button ID="btnVerify" runat="server" Text="Verify" OnClick="OnVerify" /> </div> </form> </body> </html>

Imports System.Drawing Partial Class _Default Inherits System.Web.UI.Page Protected Sub OnVerify(sender As Object, e As System.EventArgs) captcha1.ValidateCaptcha(txtCaptcha.Text.Trim()) If captcha1.UserValidated Then lblMessage.ForeColor = Color.Green lblMessage.Text = "Valid" Else lblMessage.ForeColor = Color.Red lblMessage.Text = "InValid" End If End Sub End Class

Best regards,
Lan Huang

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Robert Barnes 96 Reputation points

2024-04-30T02:09:05.0966667+00:00

Thank you Lan, I'll work through this. I'll be back to you if there's anything I don't understand. I'll add further comments if I have difficulty figuring out everything for the benefit of following readers. I'll mark "Accepted Answer" when it's running. Regards, Robert

Robert Barnes 96 Reputation points

2024-05-01T03:23:33.69+00:00

Lan, I followed your instructions, except that instead of creating a page called Default within a new project, I created a page called Demo within my existing JazzSoftware project as this is where I am having the problem. Everything appears to be OK until I tried to test my changed web site, when I got this message

1>C:\Users\OEM\source\repos\JazzSoftware\JazzSoftware\Demo.aspx.designer.vb(23,38): error BC30002: Type 'Global.MSCaptcha.captchacontrol' is not defined.

I had downloaded MSCapture by clicking the link, this has created file mscaptcha4.rar in my Downloads folder. mscaptcha4.rar contains two objects, MSCaptcha.dll and MSCaptcha.xml. What do I do to make this available to my JazzSoftware project? I think the bit I'm missing is

"you will need to add reference of MSCaptcha Library"

How do I do this?

Robert Barnes 96 Reputation points

2024-05-01T04:25:11.7133333+00:00

I followed the instructions except that I tried to create a Demo page within my JazzSoftware project. However when I came to test this the test failed with message

1>C:\Users\OEM\source\repos\JazzSoftware\JazzSoftware\Demo.aspx.designer.vb(23,38): error BC30002: Type 'Global.MSCaptcha.captchacontrol' is not defined.

I think that the issue is "you will need to add reference of MSCaptcha Library" I downloaded MSCaptcha, and I have mscaptcha4.rar in my downloads folder, but I've done nothing to add a reference to this.

Sorry, created duplicate comment by mistake.

Lan Huang-MSFT 30,086 Reputation points Microsoft Vendor

2024-05-01T05:20:18.6633333+00:00

Hi @Robert Barnes,

mscaptcha4.rar contains two objects, MSCaptcha.dll and MSCaptcha.xml.

You need to place these two files in your project's bin folder.

There is also a way to download via NuGet Package Manager（Tool->NuGet Package Manager).

Robert Barnes 96 Reputation points

2024-05-03T01:24:10.17+00:00

Thank you Lan, I've made some progress.

I tried to install MSCaptch to bin, but accidentally copied object mscaptcha4.rar not the two files, so I installed MSCaptcha using NuGet. I now see that the JazzSoftware project now includes MSCaptcha in references, and objects MZCaptcha.dll and mscaptcha.rar.

I then tried to build and run JazzSoftware, but the build failed with an error from line #54 of Web.config: -

<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\"Web\" /optionInfer+" />

(This is from the Web.Config Modifications, section <system.codedom> <compilers> )

I removed this line. Now I can build project JazzSoftware and run it with IIS Express. The home page opens and also the Contacts page, and new page Demo which opens with http://localhost:65354/demo.aspx

So I think it's all OK now. Next I'll add Captcha to Contacts and Download, which are where I really want the Captcha.

Robert Barnes 96 Reputation points

2024-05-03T04:29:43.4033333+00:00

Thanks Lan, everything is now working perfectly. Tomorrow I'll get to see if I've blocked the messages with the captcha, but at least the captcha is working as it should be on my site.
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How do I add a CAPTCHA to a web site written with ASP.NET/VB

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