How do I mitigate the HTTP Parameter Pollution vulnerability for the Captcha.aspx in the ASP.NET Web Forms application

Question

We recently scanned our web application using the Tenable web app scanning tool, and that tool detected a medium vulnerability called HTTP Parameter Pollution

That vulnerability detected a specific section within our web application, the Captcha.aspx

We don't use that component explicitly. The Captcha.aspx is a third party tool provided by Google. The only section where we mention the Captcha.aspx is the Web.config

Also we have this code in the Captcha control

protected override void Render(System.Web.UI.HtmlTextWriter writer)
{
    writer.Write("<Div><Table>");            
    writer.Write("<tr><td><img src=\"CaptchaImage.aspx?guid=" + _captcha.UniqueID + "\"></td></tr>");
    writer.Write("<tr><td><input style='width: 120px;' name=\"" + this.UniqueID + "\" type=text></td></tr>");
    writer.Write("</Table></Div>");
}

Can some one please suggest on how to mitigate that vulnerability

Answer 1

Here is what worked for me

    protected override void Render(System.Web.UI.HtmlTextWriter writer)
    {
        if (IsValidCaptcha(_captcha.UniqueID))
        {
            writer.Write("<Div><Table>");
            writer.Write("<tr><td><img src=\"CaptchaImage.aspx?guid=" + _captcha.UniqueID + "\"></td></tr>");
            writer.Write("<tr><td><input style='width: 120px;' name=\"" + this.UniqueID + "\" type=text></td></tr>");
            writer.Write("</Table></Div>");
        }
    }

    private bool IsValidCaptcha(string captchaValue)
    {
        // Implement your validation logic (length, format, etc.)
        return !string.IsNullOrEmpty(captchaValue) && captchaValue.Length <= 50;
    }