[EAI] Re: "7. Upgrading downgraded header"

[Frank Ellermann <nobody at xyzzy.claranet.de>]

Kari Hurtta wrote:

>>> | o  If each mail header has [RFC2047] encoded part and which encoding
>>> |      is "UTF-8", it may be a downgraded header, so decode it.

>>> That algorithm not necessary produce original result.

>> What differences can arise? I can see that folding may get changed,
>> and  whitespace may get mucked about, but is there anything else?

>> Changes of folding should be acceptable (and will even lead to correct
>> DKIM signature interpretation is the 'relaxed' canonicalization is
>> used).
 
> Also header field is not necessarly downgraded header field.

In other words any valid 2321 or 2047 =?UTF-8...?= encoded word could
be encoded in the original message/utf-8 (before downgrading).  Then
"upgrading" it would replace the encoded word by native UTF-8.  And
that could cause havoc for header signatures.  But we know this, the
issue has to be noted somewhere (maybe as "security consideration").

After that folks living behind a downgrade + upgrade setup have to
deal with the potential side-effects, it's anyway a shaky setup.

Frank



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