http://bugzilla.spamassassin.org/show_bug.cgi?id=3348





------- Additional Comments From [EMAIL PROTECTED]  2004-05-04 13:26 -------
Subject: Re:  base64 encoded html messages seem to confuse get_uri_list 

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Daniel Quinlan writes:
> > So...  Anyone have thoughts about this?  Part of me is inclined to leave
> > things as they are, and the other part of me says we should emulate
> > Apple Mail here and make as much valid/visible text as possible.
> 
> Maybe we should start decoding where base64 appears to begin.  I think
> we should generally follow the common behavior, but this is one case
> where we probably avoid doing the thing that doesn't let us catch the
> spam.

TBH, I don't know. IMO, it would be better to emulate what the common UAs
do.  Otherwise, we could run into a situation where a spammer can
craft a message that looks one way in common MUAs, but another way
to *us* (possibly just by having more "innocent" text after the
payload.)

- --j.

> Perhaps something like:
> 
>   first non-blank line:
>     if line is a legal MIME boundary
>       treat as a MIME boundary
>     anything else
>       treat as base64
>   all remaining lines:
>     treat as base64
> 
> Thankfully, "-" is not in base64.  However, that could open us up to
> some stupid spammer using a fake MIME boundary that is indeed decoded by
> some mailers that skip non-base64 characters (like "-") and produces a
> line of spam text.
> 
> So, a more robust technique would be:
> 
>   first non-blank line:
>     if line is a legal MIME boundary
>       decode line (raw, our MIME decoding routine simulates the more
>         common behavior of skipping non-base64 characters)
>       if decoded line is binary garbage
>         treat the line as a MIME boundary
>       else
>         treat it like base64
>     anything else
>       treat as base64
>   all remaining lines:
>     treat as base64
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