[Mimedefang] white listing $senders
Jeffrey Goldberg
jeffrey at goldmark.org
Thu Jul 8 00:00:39 EDT 2004
On Thu, 8 Jul 2004, alan premselaar wrote:
> > (1) Other than my forgetting to chomp are there other errors in the code
> > that people notice.
> >
> One thing I noticed is that you are storing your file in
> /var/spool/MIMEDefang. if you have your system configured as
> recommended with /var/spool/MIMEDefang being on a tmpfs or RAMdisk,
I haven't been following that recommendation, but I should, of course, put
the whitelist.txt file someplace else in case someday I do switch to using
a tmpsf or the like as recommended. Thanks for pointing that out to me.
> also, although the file handle should be closed once the script exits,
Yup. I've explicitely put in a close since posting my first message.
> if you're only going to whitelist based on senders who publish SPF, you
> should (if you haven't already) look into using Mail::SPF::Query.
I didn't make myself clear. I am passing mail through spf-sendmail-milter
(which calls Mail::SPF::Query) before the mimedefang filter. So anything
with an SPF fail wouldn't even reach MIMEDefang. I realize that it would
be cleaner to not use two milters and to call Mail::SPF::Query from within
mimedefang, but I haven't seen any code samples of that and a search of
the list archives produces too much noise for me to really find things.
> if your intention is to whitelist any sender who's publishing SPF
> records, then ...
That is not my intention. That would be a very foolish intention. A lot
of non-forged spam is passing SPF. What I was trying to say is that I
will only whitelist domains with appropriate SPF settings so that I can
trust $sender at this point.
> > (2) Will the whitelist file be opened anew with every incoming mail? or
> > will it only be opened when the mutliplexor starts a slave?
> >
> the way you have it configured here, everytime filter_sender is called
> your whitelist file will be opened.
>
> > (3) If the answer to (2) is "every time" is there something I can to fix
> > that while still keeping the whitelist in an external file?
> >
>
> you may want to consider using embedded perl. then you could setup your
> filehandles in filter_initialize and just reference them as approprite
> in filter_sender.
Thanks. I will take a look at that.
> > I also have a few policy questions.
> >
> > (4) What I'm doing will exempt whitelisted mail not only from defanging,
> > bad extention checks and SpamAssassin, but also from virus scanning.
> > Is that stupid? Note that at the site in question almost all (but
> > not all) email users are on Linux. Of the few MS-Windows users,
> > almost everyone (but not everyone) is using a Mozilla based MUA.
> > (But I know that there is at least one Outhouse user still, and
> > that is not going to change).
>
> Firstly, I personally am a little uneasy with setting up whitelisting
> facilities based on fields that could potentially be exploited or
> forged.
This is why I would only whitelist domains that pass SPF.
> My policy decisions are such that I scan every piece of mail thru my
> server for viruses. even outgoing mail that has been SMTP AUTH'd.
I think that that is wise. I will rethink the way I've done things to
ensure that virus scanning always happens.
> I do, however, skip spam scanning from my authenticated users as i know
> my users don't send spam. YMMV
Likewise. The consequneces of an authorized user sending spam to that
user will be a sufficient deterent.
> hope this is useful information.
Thank you, yes.
I should say that my code as posted (and as modified) doesn't seem to
work. Everything gets treated as whitelisted. But don't worry about
that. I will do some more debugging, and probably restructuring. If
after some substantial debugging, I'm still stuck, I'll ask for more help.
Cheers,
-j
--
Jeffrey Goldberg http://www.goldmark.org/jeff/
Relativism is the triumph of authority over truth, convention over justice
Hate spam? Boycott MCI! http://www.goldmark.org/jeff/anti-spam/mci/
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