[31816] in bugtraq
Re: base64
daemon@ATHENA.MIT.EDU (Christian Vogel)
Thu Sep 25 21:42:17 2003
From: Christian Vogel <chris@obelix.hedonism.cx>
Date: Thu, 25 Sep 2003 09:10:04 +0200
To: David Wilson <David.Wilson@isode.com>
Cc: Lothar Kimmeringer <bugtraq@kimmeringer.de>,
"BugTraq@securityfocus.com" <BugTraq@securityfocus.com>
Message-ID: <20030925091004.A8591@obelix.frop.org>
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In-Reply-To: <1064427873.31228.21.camel@delta.isode.net>; from David.Wilson@isode.com on Wed, Sep 24, 2003 at 07:24:29PM +0100
Hi David,
> RFC 2045 states (section 6.8):
> data, characters other than those in Table 1, line breaks, and other
> white space probably indicate a transmission error, about which a
> warning message or even a message rejection might be appropriate
> under some circumstances."
A user-agent has to assume that it's message might be dropped if it
creates base64 with junk in it. So it should not create these things
and it's perfectly resaonable for a MTA/virus-scanner to drop those
messages.
> "Because it is used only for padding at the end of the data, the
> occurrence of any "=" characters may be taken as evidence that the
> end of the data has been reached (without truncation in transit). No
> such assurance is possible, however, when the number of octets
> transmitted was a multiple of three and no "=" characters are
> present."
Again, as the mail-client does not have a way to know how the generated
data is interpreted in those ambigous cases its reasonable to just
drop those messages.
> But there are too many common email user
> agents which generate non-conforming messages.
Is there already a list of broken MUAs? Do the vendors even know
(yes, they should have cought that during testing... ;-) )
> Or should we reject all these broken messages? ;-)
Either reject them or convert them to a canonical form. But that will
generate further problems, e.g. if you modify signed payload that way.
Chris
--
Message passing as the fundamental operation of the OS is just an
excercise in computer science masturbation. It may feel good, but you
don't actually get anything DONE. -- Linus Torvalds
