Incorrect valid state on the client-side for RadCaptcha

[SUNIL]

I am using a RadCaptcha control in my web page. If I don't input anything in the textbox of RadCaptcha or enter an invalid code, then after the ajax postback returns the client-side Validity object for the RadCaptcha textbox as shown below is always showing that RadCaptcha is valid when it's not. I thought the Validity object should reflect the invalid state of RadCaptcha.  There is only one RadCaptcha in my web page.

Why is the client-side Validity object on RadCaptcha's textbox not showing the correct state? Can I check on the client-side if RadCaptcha is valid since the Validity object is not reliable. I am using Telerik ASP.NET AJAX Q2 2020 version.

[Rumen]

Hi Sunil,

I hope you are doing well!

RadCaptcha is designed primarily for server-side validation. This approach validates the user's input against the generated code on the server, where manipulation by end-users is much more difficult compared to client-side validation.

The reason client-side validation is not supported for the RadCaptcha control is due to the nature of Captcha itself. Captcha is intended to determine whether the user is a human or a bot. Performing this check on the client-side would expose the validation logic and the correct answer to the client (browser), making it easier for bots to bypass the Captcha by analyzing the client-side code. Therefore, to maintain the effectiveness and security purpose of the Captcha, validation is handled server-side.

For a better user experience, you can implement a client-side check to ensure the input field is not empty before submitting the form to the server. This can reduce unnecessary server requests when the field is left blank but won't validate the correctness of the Captcha input on the client side.

Here's a basic example of how you can ensure the Captcha input field is not empty using JavaScript:

<telerik:RadCaptcha ID="RadCaptcha1" runat="server" ValidationGroup="SubmitInfo"
    ErrorMessage="The code you entered is not valid." Display="Dynamic" ForeColor="Red">
</telerik:RadCaptcha>
<asp:Button ID="btnSubmit" runat="server" Text="Submit" Width="150px" ValidationGroup="SubmitInfo"
    CausesValidation="true" OnClick="btnSubmit_Click" OnClientClick="validateCaptcha()"></asp:Button>
 <asp:ValidationSummary ID="ValidationSummary1" runat="server" ValidationGroup="SubmitInfo"
     EnableClientScript="False"></asp:ValidationSummary>
<script>
    function validateCaptcha() {
        var captchaInput = document.getElementById("<%= RadCaptcha1.ClientID %>_CaptchaTextBox");
        if (captchaInput.value.trim() === "") {
            alert("Please enter the Captcha code.");
            return false;
        }
        return true;
    }
</script>

You would call this function on your form's submit button click event. However, this does not replace the need for server-side validation.

 

Regards,
Rumen
Progress Telerik

[SUNIL]

Hi Rumen,

I am doing good. Thanks.

I guess the Validity object is there on the client-side, but is not updated by the RadCaptcha framework for some reason.

Even, if server-side validation is needed for RadCaptcha (which I agree with you), at least the Validity object on client-side should be updated.

I am not sure if updating the client-side Validity object could cause security issues with RadCaptcha.

 

Thanks

Sunil