Re: [OAUTH-WG] WGLC on draft-ietf-oauth-v2-threatmodel-01, ends 9 Dec 2011

[Torsten Lodderstedt <[e-mail]>]

Hi Michael,

Am 04.01.2012 22:06, schrieb Michael Thomas:
> I think the "perhaps unwisely" goes to the heart of my objection. You
> might as well be talking about "perhaps unwisely" driving a car,
> or "perhaps unwisely" eating food: the reality is that people download
> apps by the *billions*.  When I was initially blown off, many of the
> participants including document editors implied that only idiots get
> apps for their phones. That is *completely* unhelpful as the reality
> is that OAUTH's use is hugely if not primarily deployed in that sort of
> environment.

I fully agree with you. That's why the core spec and the threat document 
both consider native apps.

>
> This is a threat that cuts to the very heart of what OAUTH is, and 
> purports
> to defend against: keeping user credentials out of the hands of an
> untrusted third party. If there really aren't any good ways to 
> mitigate this
> in an app environment, why is OAUTH being deployed so aggressively there?
> Shouldn't the threat draft say in blinking bold: "DEPLOYING OAUTH
> IN NATIVE APPS CONSIDERED HARMFUL"?

You lost me. Is the situation getting any worse with OAuth? I don't 
think so. I think the situation is getting better, probably not as you 
might expect.

The key question is: Why do we aim on "keeping user credentials out of 
the hands of an untrusted third party"?

1) To prevent phishing or 2) to prevent leakage of end-user credentials 
due to inappropriate handling or weak defence on the 3rd party?

wrt 1) I don't think so. I don't see how an authorization server shall 
validate the authenticity and trustworthiness of a client-side 
application. We already state this in section 4.4.1.4. of the threat 
document.

-----------------------
It is not the task of the authorization server to protect
    the end-user's device from malicious software.  This is the
    responsibility of the platform running on the particular device
    probably in cooperation with other components of the respective
    ecosystem (e.g. an application management infrastructure).  The sole
    responsibility of the authorization server is to control access to
    the end-user's resources living in resource servers and to prevent
    unauthorized access to them.
-----------------------

wrt 2) Yes, I think that's the reason. And OAuth is a appropriate 
protocol to achieve this goal, even for mobile apps. Why?

A typical mobile application consists of the app itself on the device 
and a corresponding backend service storing user data and implementing 
business and integration logic. Let's assume this application features 
address book import from other service providers. W/o OAuth, the app 
would gather the end-user's credential for a certain address book 
service and pass it to its backend service. This service in turn uses 
this credentials to access the service provider's API. So in such a 
scenario the following parties get in touch with the user credentials:
- the app
- the app's backend service
- the address book resource server

What threats do you see here? And which is most likely to occur? My 
favorite is an attack against the log files or the database of the 
backend service in order to obtain the end-users passwords for the 
resource server. Why? Because the cost/benefit ratio for an attacker is 
much better then attacking any app installation on a device and the 
protective measure on the resource server might be more appropriate then 
on the client side (backend service).

OAuth mitigates this kind of attack by reducing the number of parties 
handling user credentials to the authorization server and the user 
agent. So even if the app itself would be the user agent (which is not 
recommended), it would directly interact with the authorization server 
and the app's backend service would use tokens instead of end-user 
credentials. Moreover, the recommended way is to let the app delegate 
the flow to a trusted system component on the user's device, such as the 
system browser or an account manager. In that case, the 3rd party is not 
getting in touch with the user credentials at all.

I think the key question is whether anyone expects OAuth to solve the 
phishing problem. I don't think this is its main purpose, but it could 
facilitate to overcome the habit to enter user credentials everywhere. 
And this in turn may contribute to the fight against phishing.

regards,
Torsten.


> Mike
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