RE: [inbox] Re: [Full-Disclosure] Re: E-Mail viruses
From: Paul Szabo (psz_at_maths.usyd.edu.au)
To: Valdis.Kletnieks@vt.edu, email@example.com Date: Sat, 6 Mar 2004 08:18:27 +1100 (EST)
Curt Purdy <firstname.lastname@example.org> 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.
Paul Szabo - email@example.com http://www.maths.usyd.edu.au:8000/u/psz/
School of Mathematics and Statistics University of Sydney 2006 Australia
Full-Disclosure - We believe in it.