mailing list archives
Re: SECURITY.NNOV: Outlook Express address book spoofing
From: "Dan Kaminsky" <dankamin () cisco com>
Date: Tue, 5 Jun 2001 12:59:03 -0700
3. Now, if while composing new message G1 directly types e-mail
address g2 () mail com instead of G2, Outlook will compose address as
"g2 () mail com" <b () mail com> and message will be received by B.
What an elegant attack! Effectively, the software is doing *exactly* what
it's supposed to: Allow individuals to be mailed according to their chosen
name instead of their direct email address. But since it's rendering chosen
names in the exact same manner as the fallback direct address, by *choosing*
a name that *appears* to be a fallback address one can choose to be any name
they want to be--and since Outlook Express gives higher precedence to chosen
names than it does to direct emails, the wrong person will be mailed every
time and the user can be none the wiser.
After all, pixel for pixel, *everything* is doing just what it should.
Now, email spoofing has existed for a long time, but hasn't been abused much
since one can only *send* spoofed messages, not receive their replies. Even
Reply-To manipulation shows up in one way or another...but not this. This
is totally invisible, and I think even more effective than NNOV noted.
Incidentally, *nothing* prevents messages from being further forwarded once
they've been illicitly received. This may be one of the more dangerous
methods of executing a man in the middle attack with email alone.
Microsoft is correct that the problem is not a trivial fix: The problem is
one of user confusion, driven strongly by the fact that the user is being
shown *exactly* what they'd be seeing in a normal, non-attack scenario.
There isn't the case of a bug in the code; this is primarily a design issue.
An immediate design fix would be to use a different coloring and fontfacing
scheme to refer to full names, rather than quoted email addresses from the
address book. This should self-document decently, since over the course of
sending a number of mails users should learn to associate one character type
with one form of name and the other with the other. Then, when the attack
hits, people see things "backwards" and some method of investigation can be
made available. Things get a little sticky if you start trying to
autodetect this attack, because of situations where parts of an email
address are removed(like bob () smtp dobbs com -> bob () dobbs com, for instance),
but I think a decent method could be engineered.
Personally, a tooltip popping over an appropriately drawn chosen name
whenever the mouse was held over it would be both very useful and a decent
*Something*, however, does need to be done. Autocomplete on address book
names is easily one of the top 1% of features in OE5, and it really depends
on auto-adding on reply(which filters out spam). IT depts aren't going to
be able to get away with a mass disable of this feature, it simply won't
happen. (Things like this are moderately common when the bug attacks user
perceptions rather than simply broken code.)
Due to the severity of this issue(yes, someone might eventually hysterically
report "NEW ATTACK LETS ME READ YOUR EMAIL BEFORE YOU EVEN GET IT"), I do
think it'd be appropriate for an update in a reasonable timeframe, with
backporting to all affected platforms.
Dan Kaminsky, CISSP
Cisco Systems, Inc.