eSafe: Could this be exploited?

[Hugo van der Kooij <hvdkooij () vanderkooij org>]

Hi,

I had a bit of a chat with Aladdin support regarding the odd results I had
with their network virusscanner (aka: eSafe). (see also:
http://www.ealaddin.com/esafe/default.asp)

Both as NitroEngine or CVP server they will push as much of 80% to the
end-user before they stop a virus. Then they rely on the adding of the
exact URL so that URL can be blocked in all next requests.

If it is a first time hit you can get as much as 80% of the payload on
your machine and while they may reset the tcp stream at least IE does
store the 80% chunk as if the file was transfered correctly. (This part I
tested with over 30 different virus files.)

First off this is extremely confusing to the user who just thinks (s)he
just had a virus passing their scanner. (And they are about 80% right.)

Then the chunk may contain enough to trigger another scanner which may
reside on the desktop of said user adding further to the belief this is
not a good product.

But what if I were to write a really small harmfull virus (say less then 2
ethernet packets)? Or create it in such way that the last 20 to 25% is
expendible without loosing it's sting?

Is someone able to verify such a virus may work? (I am not a programmer so
I can think of the potential breach but I can't verify it is exploitable.)

I have a felling it is just a matter of time before such a scanner will be
bypassed.

Hugo.

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    hvdkooij () vanderkooij org         http://hvdkooij.xs4all.nl/
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            for they are subtle and quick to anger.