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*** E-MAIL viruses : restrict send/receive

Posted on 1997-09-18
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Last Modified: 2010-03-18
How to forbid Windows PPP users (connected to a Linux Intranet server running sendmail ) from sending viruses within e-mail to other users ?
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Question by:sitel
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by:jeffa072897
ID: 1586599
I've seen data from McAfee that would do it but.... you have to
put a second system in between the mail server and the network. If you're tight on IP Addresses this may not be for you.
It looks like -

Origional    

Network      Linux Box     PPP Client
            +---------+    +---------+
------------+         +----+         +
            +---------+    +---------+



Network       McAfee        Linux Box     PPP Client
            +---------+    +---------+    +--------+
------------+         +----+         +----+        +
            +---------+    +---------+    +--------+

Maybe this could help.

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Expert Comment

by:jclifford
ID: 1586600
McAfee have released a version of their VirusScan product for Linux which you could call from sendmail passing the attachments for checking.

However given that sendmail is already an enormously complecated beast I would recommend that you set up a separate machine whose wole function is to accept smtp, check it for viruses and pass it on for processing.

There are a number of advantages to doing it this way. You do not waste processing time on your mail hub, you can quarantine any virus infected files you do find, etc..

There are several commercial products which do this including Interscan VirusWall (the one I use), Dr Solomon's Mailgate, the excellent Mimesweeper, and Macafees offering which is a $7000 Linux PC with their anti-virus product installed.
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eckspurt earned 100 total points
ID: 1586601
Keep in mind that what we're calling viruses here are really trojan horses.  The recipient has to receive an e-mail with a malicious attachment and *decide to run* that attachment.  The only exceptions being where someone else has configured a user's e-mail package very stupidly, as Microsoft has been known to do.

You can *try* to scan for viruses that are in e-mail attachments, but your users can attach files according to so many different schemes, with so many different encodings, that you're fooling yourself to think you can really stop them.  You might succeed in blocking them from using standard attachments *at all*, or allow only text attachments, but that would not be secure in the least.  

What you can do is make sure your sendmail is configured so that it will only accept connections from authorized users.  You should definitely do that to prevent random spammers from making their junk mail look like it comes from your site.

For some of the best insights into Internet security issues, visit the

http://www.cert.org/
http://www.ncsa.com/virus/
http://techweb.cmp.com/iw/567/67mtsec.htm

sites.  Note that *all* of the e-mail viruses on the ncsa.com alerts page are hoaxes.  Basically anyone who tells you a firewall can block e-mail trojan horses has either been misled or is trying to sell you something.


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by:sitel
ID: 1586602
OK. But how to configure Linux to reject mail that include attachments (or that include non-text attachments ?)
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