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From: rickert@mp.cs.niu.edu (Neil Rickert)
Newsgroups: mail.uk-sendmail-workers,comp.mail.sendmail
Subject: Re: Forging messages
Message-ID: <1990Nov6.234722.8580@mp.cs.niu.edu>
Date: 6 Nov 90 23:47:22 GMT
References: <25249.9011061356@expya.cs.exeter.ac.uk>
Organization: Northern Illinois University
Lines: 34

In article <25249.9011061356@expya.cs.exeter.ac.uk> K.Sattar@cs.exeter.ac.uk (Khalid Sattar) writes:
>I have just realised that anyone on our machine which is a Pyramid
>running IDA sendmail 5.61 (or any of the suns in the campus running
>sun standard 4.0.3 supplied sendmail) that it is possible to forge a
>message to make it appears as if it came from someone else.  This is
>because sendmail allows the forger to change From, and Sender fields.
>Looking at the delivered mail I cannot find any tell tales that would
>reveal the identity of the forger.  How can I stop this?
>
 Actually this is simplistic.  The real sender appears on the Unix
'From ' line in your mailbox, or in the envelope information in mail sent
to other hosts.  Sendmail is quite careful about the envelope sender, but
makes no effort at all to authenticate the header addresses.

 Still, as many know, forging the envelope sender is pretty easy.  But why
be so alarmed about it.  Anyone can put any sender name they like on a piece
of paper add a stamp and drop it in the mail.  Or anyone can make a phone call
and claim to be whoever they like - worse still, although the telephone
companies have reasonably effective authentication methods available, the ACLU
is suing in court to prohibit their implementation.  If you come up with a
good way of preventing forgeries, expect a law suit claiming you are invading
peoples right to maintain their privacy by forging someone else's name and
address on the email.

 In the meantime, you can always personally hand deliver the message.  If
you and the recipient know each other this is a reasonably effective method
of authentication.  Even this is not completely foolproof, or else there would
be no CIA and no KGB.

-- 
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  Neil W. Rickert, Computer Science               <rickert@cs.niu.edu>
  Northern Illinois Univ.
  DeKalb, IL 60115.                                  +1-815-753-6940