RE: email address "spoofed"

["David Gillett" <gillettdavid () fhda edu>]

  Sending software, including spamming software and numerous email
worms over the past year or more, may provide any text it likes
as contents of the From: header, and routinely does.

  Your only real countermeasure is to insure that the IP address in 
square brackets in the Received: header is not really one of yours.
The usual format is something like:

Received: from name1 (name2 [IP]) by ....

where

  name1   is a string the sending host provided in its HELO packet
          to start the SMTP session (and is also often spoofed)

  IP      is the IP address that the receiving server saw the connection
          coming from

  name2   is the answer the receiving server got when it did a "reverse"
          DNS lookup on the IP address

Note that by now many SMTP servers reject mail unless they get *some*
answer on the reverse lookup; few spend much effort detecting spoofed 
HELO names, which often are made-up IP addresses or the name of the
receiving server (in hopes of bypassing any relay filters in place).

Dave Gillett


> -----Original Message-----
> From: Tim Laureska [mailto:hometeam () goeaston net]
> Sent: Friday, March 05, 2004 1:59 AM
> To: security-basics
> Subject: email address "spoofed"
>
>
>
> I'm not sure if "spoofing" is the correct term but here is what has
> happened:
>
> Someone is sending out email messages (with virus laden attachments)
> using our domain name  ... they are addressed as coming from
> support () ourdomainname com (ourdomainame would be our actual 
> domain name)
> which is an email address that we never set up.
>
> My question is how is this done and is there anything we can do to
> prevent this in the future?  The message header looks like this:
>
> Received: from your-xhtr8hvc4p [68.55.1.207] by ourdomainname.com
>   (SMTPD32-8.05) id A3C8DF0118; Fri, 05 Mar 2004 04:09:28 -0500
> Date: Fri, 05 Mar 2004 04:07:07 -0500
> To: info () ourdomainname com
> Subject: E-mail account security warning.
> From: support () ourdomainname com
> Message-ID: <oruybbfoofisdsegtve () ourdomainname com>
> MIME-Version: 1.0
> Content-Type: multipart/mixed;
>         boundary="--------hggfurquvkrsejwodibt"
> X-RCPT-TO: <info () ourdomainname com>
> Status: U
> X-UIDL: 355598192
>
>
> Tim
>
>
>
>
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Ethical Hacking at the InfoSec Institute. Mention this ad and get $545 off 
any course! All of our class sizes are guaranteed to be 10 students or less 
to facilitate one-on-one interaction with one of our expert instructors. 
Attend a course taught by an expert instructor with years of in-the-field 
pen testing experience in our state of the art hacking lab. Master the skills 
of an Ethical Hacker to better assess the security of your organization. 
Visit us at: 
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