[MAILSCANNER] Reverse NDR attack.How to combat ? Any ideas ?

Matt Kettler mkettler at EVI-INC.COM
Wed Sep 21 00:18:35 IST 2005

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Venkata Achanta wrote:
> Hello List,
> http://computer-vet.com/weblog/2004/06/11/reverse_ndr.html
> My setup MS e-mail gatway relaying for exchange 2000.Upgrading to Xchange 
> 2000 is in the works still as we have 1000's of users. My outbound Q on the 
> mailscanner box is 6k with tonnes of NDRs,delaying legitimate e-mail. This 
> started a week ago MS doing its job perfectly but still .....there should 
> be a way to stop this attack.
> Accepting e-mail only for legit exchange users on the mailscanner gateway 
> is also not helpful for this kind of attack.

Yes it is a way of preventing the attack, or at least it's a way of preventing
you from being used as a "relay".

In order for a reverse NDR attack to work you MUST first accept the message,
then later generate a bounce DSN.

Set up your mailscanner box to only accept valid users and your problem will

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