Götz

On 9/17/2009 11:40 AM, Götz Rieger wrote:
> Hi all,
>
> I've got an issue with amavisd-new banning emails which start with a
> special character (accented E, Hungarian) like in "és " as ms-exe.
> System is SLES 10 SP2, amavisd-new is fairly recent, I've got to look up
> the exact version.
>
> Enconding is:
> Content-Type: text/plain; charset=ISO-8859-2
> Content-Transfer-Encoding: 8bit
>
> It looks like the Hex representation of the character and MS-DOS COM is
> the same, 0xe9.
>
> Funny enough in newer SuSE versions the line
>
> 0      byte            0xe9            DOS executable (COM)
>
> is commented out in /usr/share/misc/magic, in SLES 10 SP2 it's
> uncommented. So if amavisd-new is using "file" (it does, does it?) it's
> blocked correctly.
>
> But I need to have those emails get through. So my dilemma is:
>
> -Should I just comment the line and risk old style DOS COM executables
> to go through (pretty rare occurence I would say but anyway...)
>
> -Or does anybody know a better way? I reckon using quoted-printable as
> transfer encoding instead of 8bit would avoid the problem, too?
>
> Would be nice to get some thoughts.
>

I would comment them out personally, if you have email in charsets and 
languages that might cause FPs.

Clearly the simplistic single-byte DOS executable tests are inadequate 
to meet today's requirements.  There is also (ë = 0xeb and non-breaking 
space = 0x8c):

   0       byte            0x8c            DOS executable (COM)
   0       byte            0xeb            DOS executable (COM)

And there might be others that hit too.

You could do any/all of the following:

a) check out the latest (cvs) version of file(1) to see if the issue has 
been addressed: it is still a problem in 5.03.

b) comment out the offending magic entries

c) contact the file(1) maintainer Christos Zoulas over at 
http://mx.gw.com/mailman/listinfo/file at get some advice/suggestions.

d) create your own magic entries in $HOME/magic or $HOME/magic.mgc 
(where $HOME is amavis' $HOME) that catch and usurp detection for the 
most common cases for your situation (eg, here's one for "és"):

   0       string            \xe9\x73            ISO-8859 text

Downsides with this solution are 1) you'll need a number of 
permutations, and 2) any might overlap with actual DOS executables, 
effectively implementing solution (b) above.

e) create and amavis entry to allow DOS executables returned from file.

Hope this helps.
--
Mike



-- 

      Mike

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