Posted by Michael Vilain on 01/24/08 20:00

In article <fn9548$uqm$1@aioe.org>, Manuel Lemos <mlemos@acm.org>
wrote:

> Hello,
>
> on 01/24/2008 02:40 AM Shelly said the following:
> >>> The email is only sent to the site owner, so the spammer has no way of
> >>> knowing what the email should look like. That tells me that they have
> >>> to be going through the form. Yet the proper email has an echo of
> >>> generated security code. The spam email has that field empty. So,
> >>> that says he can't be going through the form.
> >>> It seems to me that they must:
> >>> 1 - Somehow diverting a legitimate email so that copy is sent to
> >>> them.
> >>> 2 - Using that email copy to create a template and modify the output
> >>> so that junk is sent.
> >>> I really don't know how they are doing it.
> >> If you are not using a good CAPTCHA, I am not sure what you mean by
> >> security codes.
> >>
> >> Anyway, I suspect that your code has a common vulnerability of contact
> >> forms which is to not properly encode information that goes to message
> >> headers. This means that if the abuser inserts a well throught character
> >> sequences, he may make your script compose a message that uses your mail
> >> server to send spam to anybody in the world.
> >>
> >> It is hard to advise without seeing your script. Anyway, I recommend
> >> using a component that knows how to properly encode or escape malicious
> >> character sequences to avoid abuses like your suffering.
> >>
> >> I use this MIME message composing and sending class that is well aware
> >> of all the e-mail standards that are necessary to compose messages
> >> properly. You may want to use it to avoid the abuses.
> >>
> >> http://www.phpclasses.org/mimemessage
> >>
> >
> > I use the class htmlMimeMail from http://www.phpguru.org/ by Richard
>
> I have not studied that class. I don't know if it properly encodes
> message headers.
>
>
> > Heyes. The security code is just a randomly generated string of 6
> > characters. I am not using a CAPTCHA. I guess I will have to.
>
> That may explain it. Even some CAPTCHAs can be bypassed with good OCR
> scripts. But even a basic CAPTCHA can raise the bar hard enough to make
> your abuser give up.

I use a very simple trick. Put a HIDDEN field with an obvious name like
"COUNTRY" or "POSTAL CODE" or whatever giving it an initially blank
value. Check in the post processing for the form to see that it's
blank, meaning the form was filled out by a browser with a human sitting
in front of it. If a bot filled out the form, chances are it put in a
value. Throw those submissions away and do nothing. Mail the others.

--
DeeDee, don't press that button! DeeDee! NO! Dee...

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