On 9/11/06, 3APA3A <3APA3A (at) security.nnov (dot) ru [email concealed]> wrote:
> BE> Two-factor auth cannot be said to make accessing the network from a
> BE> compromised PC "safe". That does not make two-factor auth useless.
> BE> With plain passwords, once the attacker has the password, they can
> BE> access the network at will. With two-factor auth, they can access
> BE> the network for a much more limited time span.
>
> Network is compromised as long as attacker keeps control under
> compromised host regardless of authentication. And sometimes longer.

I think we're talking about different kinds of environments and
authentication schemes. The example I had in mind was this one:

- corporate web mail system requires two-factor auth for access
- employee accesses the web mail system from a friend's machine that
is loaded with spyware, authenticating using their token.
- the spyware has access to the web mail system for as long as the
token is in the machine
- once the token is removed, the spyware can continue accessing the
web mail system until the web mail system session expires

So the damage is limited to what is stolen during the session, while
with a password-only system the account could be used for an
indefinite time period, i.e. until password change.

<snip NTLM example>
> It means, if authentication schema is NTLM-compatible (it must be for
> compatibility with pre-Windows 2000 hosts and some network applications,
> like Outlook Express), attacker can use compromised account to access
> network resources without having access to 2-factor authentication
> device. How long he can retain this access depends on how often
> account's NT key is changed (usually with password change, but actually
> depends on implementation of authentication system and may be never).

Is this RSA whitepaper an example of what you are talking about?

http://tinyurl.com/pb5n7

The whitepaper refers to Kerberos tickets, but the mechanism sounds
like it could work with NTLM as well.

I think the situation you are pointing out is where an authentication
process requires an initial two-factor authentication, but then issues
some kind of session key that takes a very long time to expire. That
would seem to defeat the purpose of the two-factor auth.

Regards,
Brian

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