[Mimedefang] Watermarking locally submitted messages [was: Mimedefang/logwatch interaction]

[David F. Skoll]

Philip Prindeville wrote:

> And then in filter_begin() we could test for the
> presence of this line, if it's present and contains
> the correct value, then we accept the message with no
> further filtering...

That would work.

An alternative method that doesn't require modifying submit.cf
(pseudocode):

IF source address != 127.0.0.1 THEN
   IF we are re-mailing for any reason THEN
      ADD an X-MIMEDefang-Remailed: magical-gibberish-header to the remailed msg
   ENDIF
ELSE
   IF Message has our magical X-MIMEDefang-Remailed: header THEN
      # It was remailed... filter as usual
      REMOVE the X-MIMEDefang-Remailed: header
   ELSE
      # It is locally-submitted.  Do not filter
   ENDIF
ENDIF

That way, if the header leaks out, it only permits an attacker to
make you handle his message *more aggressively* than usual.

Regards,

David.