[Mimedefang] Re: dictionary attacks looking for a valid user

Joseph Brennan brennan at columbia.edu
Thu Dec 29 20:21:39 EST 2005

--On Thursday, December 29, 2005 12:23 PM -0800 Kelson Vibber 
<kelson at speed.net> wrote:

> Joseph Brennan wrote:
>> To some extent I've reduced the problem with--
>>     define(`confBAD_RCPT_THROTTLE', `2')
>> --in sendmail.mc, cutting down on how many addresses they can check.
>> The concept was that zombies don't queue and re-try.  However our logs
>> recently have evidence that now they do re-try.
> Um.... that doesn't cut them off after two hits, it just causes the
> server to pause before acknowledging each subsequent recipient the client
> asks for in that session.

Right.  I quoted the wrong section.  This is what does it, where
nn.nn.nn.nn are numeric IPs of a few local mailing list hosts that
I am not revealing here:

Karith arith
C{listhost} nn.nn.nn.nn nn.nn.nn.nn
R$*                     $: $1 $| $&{client_addr}
R$* $| $={listhost}     $@ OK
R$* $| $*               $: $1 $| $( arith l $@ $&{nbadrcpts} $@ 3 $)
R$* $| FALSE            $#error $: 450 Too many bad recipients

Joseph Brennan                  Columbia University Information Technology
                                postmaster at columbia.edu

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