Re: [websec] [Technical Errata Reported] RFC6797 (4075)

Yoav Nir <ynir.ietf@gmail.com> Fri, 08 August 2014 21:16 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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To: Eric Lawrence <e_lawrence@hotmail.com>, Barry Leiba <barryleiba@computer.org>
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Cc: Jeff Hodges <Jeff.Hodges@paypal.com>, Pete Resnick <presnick@qti.qualcomm.com>, "websec@ietf.org" <websec@ietf.org>, Collin Jackson <collin.jackson@sv.cmu.edu>, RFC Errata System <rfc-editor@rfc-editor.org>
Subject: Re: [websec] [Technical Errata Reported] RFC6797 (4075)
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On Aug 8, 2014, at 10:54 PM, Barry Leiba <barryleiba@computer.org> wrote:

>> I'm afraid I'm only a consumer of RFCs and thus I'm not sure I understand
>> the distinction here. To me, it seems that the RFC's threat model is
>> incomplete.
> 
> Perhaps it is, but the distinction is about whether an error was made
> in writing the document, or whether there's a flaw in the protocol, an
> issue that wasn't considered in the discussion, or the like.
> 
> The sentence you're addressing is entirely consistent with the rest of
> Section 14.4, and doesn't look like "errata" to me.  It's quite
> possible that the working group blew it and should have thought about
> things differently.  It's possible that someone should write an update
> to RFC 6797 to correct it, and that your input would be useful.
> 
> But you're asking the websec working group to consider an update, not
> making an errata report, as I see it.
> 
> Does anyone from websec have a comment on this?

Hi Barry.

Reading this, it doesn’t look like an error in the document, but as an attack that the group may not have considered, which HSTS may not protect. If this is indeed valid, and if this had been caught in IETF last call or IESG review, this would probably have been sent back to the working group to complete.

Eric: I’m trying to understand the issue, so please see the below and tell me if I understood it correctly. 

Suppose we set up secure.tools.ietf.org and a sub-domain of tools.ietf.org and set HSTS on that domain (but not on tools.ietf.org, which is available in HTTP)
I browse http://tools.ietf.org. Because I’m not using HTTPS, an attacker intercepts the connection and injects a cookie for all subdomain (Path=/; Domain=tools.ietf.org). 
My next connection to https://secure.tools.ietf.org will send this cookie.

Did I get this correctly?

So my first reaction was “No way. You can’t set a Secure cookie over an HTTP connection, can you?  Just like you can’t set HSTS over an HTTP connection.” So I went to find where in RFC 6265 it says that. So of course it doesn’t.  Googling it shows that I’m not the first to wonder about that. In anyone has some insight about this, I’d be glad to know. Is it just that cookies have always worked like this, so we’re not changing it now?

Unless I’m missing something, this could be a real problem, and there are several ways to mitigate it. Any of them requires a new document that either replaces 6797 or updates it ( I can see this solved with a 2-page + boilerplate document). But I don’t think an errata report is the way to go on this.

Yoav