Re: [Exim] Stopping loops

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Author: Nigel Metheringham
Date:  
To: Chris Knipe
Subject: Re: [Exim] Stopping loops
cgknipe@??? said:
> While none of the accounts has to be located on the same machines or
> anything as such, spam@??? is going to get a awefully lot of
> mail, especially should there be added a 1MB attachment to the email
> that will "infinately?" loop through Accounts A and B.


The loops will be restricted on any sane mail system - the number of 
hops a mail message can go through is restricted - on exim the option 
is received_headers_max and defaults to 30
    http://www.exim.org/exim-html-3.10/doc/html/spec_11.html#SEC306


If both A & B are local then I think that the loop resolution and
collapsing of repeated addresses will cause this to be rather less
effective [a quick test shows that this is the case and the victim
address gets only one copy]

> For every
> successfull loop, spam@??? gets 2 email messages. What
> happens when you put in 5 addresses in the loop? or even 10? 10MB of
> email, through one loop, and then you keep it running for a few days,
> and you can even take out complete servers with this, should hard
> drive space run out on the server (1GB of email in one mailbox?).
> Something which can be quite destructive hey? Or is it perhaps
> allready protected?


Quotas will help on this. You do need to keep feeding messages into
the loop for decent effect. If someone tried this on a machine where I
work I would have them shown the door in pretty short order, and it
would certainly be prosecutable under UK Computer Misuse law as I
understand it (although getting police interested would be close to
impossible - so I guess it would have to be a private prosecution for
theft of service).

    Nigel.
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[ Nigel Metheringham                  Nigel.Metheringham@??? ]
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