On 16 Jan 2002, Bill Kenworthy wrote:

> On Wed, 2002-01-16 at 01:45, Tzafrir Cohen wrote:
> > On 15 Jan 2002, Bill Kenworthy wrote:

> > > It picks up the usual virii attachments quite
> > > reliably, defangs html mail (embedded scripts etc in the html) and also
> > > perl/shell scripts etc (inserts an "exit" statement and comment at the
> > > top of the file so it cant be run by accident!)
> >
> > Sounds very intrusive to me.
>
> How paranoic are you? - i.e., this is the preference (or specification
> worked to) by many people. Its only mildly intrusive and my family use
> mail lists that love cute html things and this is a bit safer. and no,
> one cannot turn off incoming html mail (a popular uprising would occur!)
> - some of the lists have no alternatives! We also get the odd html
> carried virus and this picks up and sanitises them quite reliably.

hint: netscape/mozilla allows you to disable javascript separatly on the
mail client.

> >
> > A decent mail program does not execute scripts. If my mailer (OK, it
> > probably has a number of buffer overflows somewhere, but it is rather sane
> > apart from that) gets some script, it simply displays it to me.
> >
> > Now if some support guy sent Joe User a script to use, he had to work
> > around those strange (=unexpected) limitations
> >
>
> Now if someone set up a mimetype in evolution for say, perl and
> misclicked one time...
> Not likely, but it could happen. Also, one place I have worked had a
> number of developers working in windoze with perl and the windoze unix
> and shell environment (cant remember the name - mental block!!!) which

cygwin

> would be at risk of executable shell scripts for all the usual windoze
> reasons.
>

Then go to their systems and configure them properly! Anyway, blocking is
betteer than modifying. You should generally assume that at least 99% of
the suspects are innocent in this case. If you block, the user will know
that a workaround is required. If you modify: the user may not know that.

Anyway, I can think of more creative ways of shooting myself in the foot.

Have a look at the standard mailcap in the mime type
application/x-metamail-patch (this was remmed-out when I upgraded from 7.2
to 8.1) for one such creative way.

> > > It can also call a true
> > > virus scanner to scan documents you want to let through, but need
> > > checking internally.
> >
> > IMHO you should not try to overly clean. I rather have a virus scanner
> > bounce a message than trying to clean it, and possibly creating an
> > incorrect content.
> >
>
> personnel pref. Also not clean, rather look inside a file and see if it
> does contain a virus, rather than just bounce based on criteria - its
> flexible! At one time I did have anomy set to bounce, but I dont trust
> the return address any more. I have heard that there is at least one
> virus that trys to fake the header.

So what? So you get an error message. But it is not a DoS, as you only
send out one message for every message that you recieve (unless you bounce
on delivery. In this case one message can cause many bounces!)

Again: don't let the guilty tamper your handling of the innocent.

> > > The documents have some discussion on performance
> > > tuning, which from memory was quite acceptable considering what it is
> > > doing.A good first line for Linux users and
> >
> > For linux users?
> > Linux users have decent mail clients (read: not many people used Outlook
> > & co. on linux lately)

Err...

Are linux clients better? (not to mention the latest flop of pine)

I tried kmail. Just like a typical windows program, it has no notion of
"view" a file. Only "open". Naturally you "open" a jpg image with an image
viewer and a shell script with /bin/sh . In both cases you get the same
scary warning dialog. People get used to this dialog crying wolf on
images, and simply ignore it.

Solution: the approach of mailcap: allow only to "view" attachments by
default, never to "run" them.

-- 
Tzafrir Cohen
mailto:tzafrirtechnion.ac.il
http://www.technion.ac.il/~tzafrir

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