Subject: Re: [Unbearable] Potential privacy bug if Include-Referer-Token-Binding-ID is improperly implemented client-side

From: =JeffH <[email-masked]>
Date: Tue, 22 Mar 2016 18:10:53 -0700

thx for clarifications, Nick. further questions & thoughts..

 > Here's the problem: Suppose the connection to server A is over http.
 > Now a network attacker B injects into some http page (from server C) code
 > that will cause the client to make an http request to server A.
 > The attacker B intercepts the request and responds with a redirect to
 > server B (with the Include-Referer-Token-Binding-ID header).

the redirect to B will be an HTTP 30x response not over TLS, regardless of 
whether the Location: header field contains a https URI, yes?

 > The client
 > dutifully follows that request and forwards the TokenBindingID it has for
 > A to the attacker-controlled B.

Should we not explicitly stipulate in -tokbind-https that the client MUST 
NOT honor any Include-Referer-Token-Binding-ID header received over insecure 
transport? This is how we addressed similar situations in the HSTS and HPKP 
specs.

 > It would certainly be nice for the transport to be established error
 > free, and to use HSTS and HPKP, but I don't think those need to be made
 > as requirements for using Token Binding.

I was not proposing stating any requirements wrt employing HSTS and HPKP -- 
rather, I am thinking that we should have some deployment considerations 
where HSTS and HPKP are dutifully mentioned and how their use composes with 
TB to the benefit of the web app provider and their users.

HTH,

=JeffH

---

From: Nick Harper <[email-masked]>
Date: Tue, 22 Mar 2016 18:15:29 -0700

On Tue, Mar 22, 2016 at 6:10 PM, =JeffH <[email-masked]>
wrote:

> Correct.

> NOT honor any Include-Referer-Token-Binding-ID header received over
> insecure transport? This is how we addressed similar situations in the HSTS
> and HPKP specs.
>
> The addition of
https://github.com/TokenBinding/Internet-Drafts/commit/2033a64397590a55811cb78af8f5aa739cb8c981
implicitly states that (since the Token-Binding header is not sent over an
insecure transport). I don't have strong feelings for whether this needs to
be more explicit.

> I was not proposing stating any requirements wrt employing HSTS and HPKP
> -- rather, I am thinking that we should have some deployment considerations
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