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

[Philip Parsons]

I use a tool called qtool.pl which scans the mail queue for any "User
unknown" every hour and then deletes the mail from the queue.

-----Original Message-----
From: MailScanner mailing list [mailto:MAILSCANNER at JISCMAIL.AC.UK] On
Behalf Of Matt Kettler
Sent: Tuesday, September 20, 2005 4:19 PM
To: MAILSCANNER at JISCMAIL.AC.UK
Subject: Re: [MAILSCANNER] Reverse NDR attack.How to combat ? Any ideas
?

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 evaporate.

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