How to get request source in asp?

HTTP_REFERER does not guarantee any security , it is very easy to overwrite it and to defraud the source since it is a header.

The best thing to do in order to ensure the origin of the form could be using reCAPTCHA

Also try out techniques like protection anti-CSRF means Cross-Site Request Forgery ), it is not 100% efficient, but it works better than HTTP_REFERER , an example of SOen (I just do not know if md5 is really something needed)

I think it would look something like:

• All pages that receive a request or have a Form or an Ajax must (can put in global or in a function):

  Function GetGUID()
  
      GetGUID = CreateObject("Scriptlet.TypeLib").GUID
  
  End Function
  
  Dim token
  
  ' Só atualiza o valor da sessão se não vier de um POST
  ' com '<input name=csrftoken>'
  If Request.Form("csrftoken") = "" Then
      token = md5(GetGUID())
      Session("token")=token
      Session("token_time")=Time()
  End If
  

• On the page receiving the POST / request you should have this:

  If Request.ServerVariables("REQUEST_METHOD") = "POST" Then
      ' Compara o Form com a sessão
      If Request.Form("csrftoken") = Session("token") Then
          ' Executa o seu código aqui !!!
      End If
  End If
  

• In form you should also add Session("token")

  <form method="post" action="pagina.asp">
      <input type="text" name="foo" placeholder="Exemplo">
      <input type="submit" value="submit">
      <input type="hidden" value="<%= Session("token") %>" name="csrftoken">
  </form>
  

  

For a long time I have not worked with classic asp, if you have any typos are free to fix them

How to Fool the Referer and Origin

With Postman or