[35484] in bugtraq
Re: Is predictable spam filtering a vulnerability? (silently dropping
daemon@ATHENA.MIT.EDU (der Mouse)
Thu Jun 24 21:00:18 2004
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
Message-Id: <200406232257.SAA10382@Sparkle.Rodents.Montreal.QC.CA>
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Date: Wed, 23 Jun 2004 18:46:55 -0400 (EDT)
To: bugtraq@securityfocus.com
In-Reply-To: <Pine.LNX.4.58.0406222049440.7290@shishi.roaringpenguin.com>
OK, I'll brave the storm of broken autoresponders one more time....
>> IMHO 3: If user Joe gets 10 delivery failures of messages that he
>> has not sent and one delivery failure of message that he has
>> actually sent, it is worse than if he gets nothing.
> This is indeed a problem, and it's a loophole that needs to be
> closed.
Unfortunately it's difficult for most people to close.
> There needs to be a way for an SMTP server to correlate a bounce
> message with a sent message, and reject the bounce message if it
> wasn't caused by a validly-sent message. Proposals like SPF can help
> a little.
A little. But there also is a need to _identify_ bounce messages.
A few years back, I got joed - some lamer forged my address into the
from-line of what appears to have been an entire spamrun. I got some
small number of thousands of bounces before I taught my mailer to pick
apart multipart/report bounces and reject them if the bounced message
doesn't show certain signs that all messages I send show. This helped
immensely, and when the modern crop of from-line forging malware showed
up, my defenses were already in place and functioning.
Today, I occasionally get bounces for malware with my address forged
into the fromline. I respond to them with a more or less stock
response that goes something like
If you _must_ do accept-and-bounce (something which is
increasingly "part of the problem" in today's net), please at
least make sure your bounces are proper multipart/report
bounces, so they can be mechanically identified and treated
appropriately. (See RFC 3462 for more on multipart/report.)
I've been doing this only a little while. If there comes to be a site
which is a persistent source of bounces and also persistently ignores
that request, I'm prepared to block it entirely.
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