RE: [inbox] Re: [Full-Disclosure] Re: E-Mail viruses

[psz@xxxxxxxxxxxxxxxxx (Paul Szabo)]

Curt Purdy <purdy@xxxxxxxxxx> wrote:

>>> An alternative is to allow only a proprietary extension through,
>>> like .inc.  Legitimate senders would rename the file, be it .exe
>>> .doc .jpg, indicate in the body of the message what the true
>>> extension is, and the receiver merely renames it.
>>
> Only the proprietary extension, i.e. .inc or .xyz or .whatever,
> would be allowed through, and since virus writers would never use
> this extension, it would eliminate ALL viruses at the gateway.
> The nice thing about this approach is that it completely eliminates
> the need for any anti-virus on the mail server since all virus
> attachments are automatically dropped without the need for scanning.
> Quite a simple, yet elegant solution, if I do say so myself.

Yes, it eliminates a large class of viruses. But, it would not do
anything to "local" attacks (a virus modified specifically to handle
your particular setup; and if it becomes widely used then "real"
viruses will also do the same).

Also it does nothing to viruses that do not use attachments: attacks
on a "Subject:" buffer overflow, or a virus delivery via the web with
a link or "Content-type: message/external-body".

Also you might miss some attachments: "uuencoded block"s, or those
within incomplete "Content-type: message/partial" bits.

Within those limitations, it is a great idea to keep an organization
free from "common" attacks.

Cheers,

Paul Szabo - psz@xxxxxxxxxxxxxxxxx  http://www.maths.usyd.edu.au:8000/u/psz/
School of Mathematics and Statistics  University of Sydney   2006  Australia

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