--- Tony Finch <dot@???> wrote:
> On Tue, 27 Apr 2004, Andrey Tverdokhleb wrote:
> >
> > Well, I'm asking actually because I heard that
> STARTTLS without EHLO is
> > some kind of security threat and would be
> interested in getting more
> > details if this is true.
>
> If instead of checking the server's ESMTP service
> extension list you just
> try STARTTLS and fall back to cleartext SMTP if it
> fails, you make it
> easier to perform a man-in-the-middle security
> downgrade attack since
> STARTTLS is the first thing you say. The attack is
> still possible if you
> follow the protocol correctly but it requires
> modification of later parts
> of the TCP stream. There's more about this in 3207.
>
You meant RFC 3207. It took me whole 30 sec. to figure
out what is 3207 :)
Thank you for hint. Attacks description in the
document is rather brief, but I think it's serious
enough to be taken care of. This looks like popular
vulnerability, MS Exchange for example is vulnerable,
even though it doesn't allow STARTTLS as the first
command, but to convince him HELO is enough, which is
not good at all since STARTTLS still not advertised.
And I still can't find any security advisory on this topic.
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