Re: base64

["Ilya Teterin" <alienhard@xxxxxxx>]

David Wilson:

> So, there is ambiguity in RFC 2045, and this is the point of the
> original post. Different people, and therefore different
> implementations will have different interpretations. There is
> therefore potential for a vulnerability when checks are
> performed using one interpretation but the actual receiver
> uses another interpretation.

Thanks. It's exactly what I mean. Please note that if there is no "correct" 
interpretation of RFC 2045, then *any* implementation of decoding is 
"vulnerable" to ambiguity issue, and we need workaround when it's dangerous. 
So, at least all antiviral software which are not aware of this issue should be 
patched as soon as possible :-) We can meet mail worm, which is polymorphic at 
the attachment encoding level, and can't be detected without modification of 
core files of antiviral software.

> Or should we reject all these broken messages? ;-)

I believe we should reject ambiguous messages, if and only if it's ambiguity 
related to content-filtering rules.

So, if we check base64 attachments for viruses or spam, we should reject 
messages with malformed attachments. If timezone field is malformed and there 
are no filtering rules related to timezone - we have no reasons to reject this 
message.