Re: AD review of draft-ietf-httpbis-alt-svc-10

I like that rewrite.

On Fri, Jan 15, 2016 at 8:00 PM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> Does that suggest an "unless" or a rewrite to something like:
>
> Clients that wish to prevent requests from being correlated (such as
> those that offer modes aimed at providing improved privacy) SHOULD NOT
> use alternative services for multiple requests that would not
> otherwise be allowed to be correlated.
>
> On 16 January 2016 at 08:22, Chris Bentzel <chris@bentzel.net> wrote:
> > That seems reasonable.
> >
> > On Fri, Jan 15, 2016 at 4:10 PM Mike Bishop <
> Michael.Bishop@microsoft.com>
> > wrote:
> >>
> >> The concern goes the other way, too – Alt-Svc mappings that you’ve
> >> previously discovered continuing to be used in Incognito.  If a server
> gave
> >> you an Alt-Svc of “chrisbentzel-laptop-2.tracking.example.com”
> previously
> >> and you used it once you entered Incognito, they could persist your
> identity
> >> into that mode regardless of whether you persist updates you see while
> >> Incognito.
> >>
> >>
> >>
> >> Having a separate cache of Alt-Svc mappings that gets used only for that
> >> session would seem like a reasonable mitigation.
> >>
> >>
> >>
> >> From: Chris Bentzel [mailto:chris@bentzel.net]
> >> Sent: Friday, January 15, 2016 1:04 PM
> >> To: Mark Nottingham <mnot@mnot.net>; Stephen Farrell
> >> <stephen.farrell@cs.tcd.ie>
> >> Cc: Mike Bishop <Michael.Bishop@microsoft.com>; Barry Leiba
> >> <barryleiba@computer.org>; Julian F. Reschke <julian.reschke@gmx.de>;
> >> draft-ietf-httpbis-alt-svc@ietf.org; HTTP Working Group
> >> <ietf-http-wg@w3.org>
> >>
> >>
> >> Subject: Re: AD review of draft-ietf-httpbis-alt-svc-10
> >>
> >>
> >>
> >> Chiming in (very) late on the "In particular, clients configured for
> >> anonymous usage SHOULD NOT use alternative services."
> >>
> >>
> >>
> >> I'm actually not sure what folks here have in mind when they think of
> >> "anonymous usage" configurations.
> >>
> >>
> >>
> >> Assuming that something like Chrome's Incognito Mode falls under that
> >> bucket, it is likely that Chrome would use alternative services within
> an
> >> incognito session but not persist the alternative service mappings -
> they'd
> >> go away when the incognito session ends.
> >>
> >>
> >>
> >> On Thu, Jan 14, 2016 at 10:32 PM Mark Nottingham <mnot@mnot.net> wrote:
> >>
> >> In some side discussions, I've come across other people who are unhappy
> >> with this state of affairs, so I don't think you're alone. I'll leave
> it up
> >> to them to decide how to participate here.
> >>
> >> To be explicit -- we are opening up a potential same machine attack
> >> (specifically, someone on a shared HTTP server who has the ability to
> both
> >> add response headers -- such as with .htaccess or a CGI script -- and
> listen
> >> to another port (possibly, ANY port) on the same box can then hijack
> traffic
> >> intended for other users.
> >>
> >> The motivation for doing so is to enable the HTTP Opportunistic Security
> >> specification, which offers weak protection against pervasive monitors,
> but
> >> is vulnerable to active attackers, and doesn't improve Web security in
> other
> >> (and important) ways that HTTPS does. We have only one implementation of
> >> that specification in a browser, and no sign that it will be adopted by
> >> others.
> >>
> >> Is this a reasonable tradeoff? We are planning to publish this is
> >> Experimental, so the question might also be "is this a responsible
> >> experiment to run?"
> >>
> >> Cheers,
> >>
> >>
> >>
> >> > On 14 Jan 2016, at 6:18 am, Stephen Farrell <
> stephen.farrell@cs.tcd.ie>
> >> > wrote:
> >> >
> >> >
> >> >
> >> > On 13/01/16 19:16, Mike Bishop wrote:
> >> >> Yes, that's obviously a mitigation servers can set up, but that means
> >> >> we're telling existing servers they need to disallow something that's
> >> >
> >> > Well s/need/can/ I think, but sure.
> >> >
> >> >> newly defined in order to prevent their users from hijacking them.
> >> >> And I don't believe retroactive guidance like that is reasonable --
> >> >> that will lag actual deployment of the protocol, and will never be
> >> >> 100%.
> >> >>
> >> >> My proposal was that ~eve remains able to advertise an Alt-Svc, but
> >> >> that alternative must then authenticate itself as users.example.com
> >> >> (which Eve's proxy cannot do) before clients will use it.
> >> >>
> >> >> I remain a little unhappy with this as it stands, but if no one else
> >> >> thinks it's a problem, I'll stop now.
> >> >
> >> > Yeah, ditto:-)
> >> >
> >> > Cheers
> >> > S
> >> >
> >> >>
> >> >> -----Original Message----- From: Stephen Farrell
> >> >> [mailto:stephen.farrell@cs.tcd.ie] Sent: Wednesday, January 13, 2016
> >> >> 2:19 AM To: Barry Leiba <barryleiba@computer.org>; Mike Bishop
> >> >> <Michael.Bishop@microsoft.com> Cc: Julian Reschke
> >> >> <julian.reschke@gmx.de>; draft-ietf-httpbis-alt-svc@ietf.org; HTTP
> >> >> Working Group <ietf-http-wg@w3.org> Subject: Re: AD review of
> >> >> draft-ietf-httpbis-alt-svc-10
> >> >>
> >> >>
> >> >> Hiya,
> >> >>
> >> >> Yes, I'm fine that ~eve in Mike's scenario can muck with ~alice as
> >> >> specified. (And such servers still do exist, we have one still.)
> >> >>
> >> >> I'd say best would be to call that attack out in the draft, but I
> >> >> don't think the mitigation for the misbehaviour is to authenticate
> >> >> ~eve, which is what the text below seems to be saying. Authenticating
> >> >> the web server for the name will help of course, but surely the real
> >> >> mitigation for that attack is for the server to scrub the alt-svc
> >> >> headers? (And to be clear, yes the port number thing is fine, I don't
> >> >> think system ports is a deal these days.)
> >> >>
> >> >> All of the above of course also assumes that the "changing host"
> >> >> stuff is worked out well, which I'm sure it is or will be, but
> >> >> haven't checked.
> >> >>
> >> >> S
> >> >>
> >> >> On 13/01/16 00:34, Barry Leiba wrote:
> >> >>> The point with all this, in my mind and with respect to the text we
> >> >>> have, is whether it makes any practical difference any more
> >> >>> whether Eve sets this up on port 23412 or on port 1000.  My
> >> >>> contention is that it doesn't, these days (while it might have in
> >> >>> the past), and that implying that it's safe if the alt-svc is on a
> >> >>> low-numbered port, but not safe (or less safe) if it's on a
> >> >>> high-numbered port isn't doing any service to anyone.
> >> >>>
> >> >>> I think we should alert people to the possible
> >> >>> attack/issues/whatever, but that we should not imply that any set
> >> >>> of ports enjoy any sort of immunity against or resistance to those
> >> >>> attacks.
> >> >>>
> >> >>> b
> >> >>>
> >> >>>
> >> >>> On Tue, Jan 12, 2016 at 5:09 PM, Mike Bishop
> >> >>> <Michael.Bishop@microsoft.com> wrote:
> >> >>>> More whether you're okay with that text as mitigation to this
> >> >>>> hypothetical attack:
> >> >>>>
> >> >>>> http://users.example.com is a shared server which hosts user home
> >> >>>> pages.  Eve places a config file in her wwwpages directory to add
> >> >>>> an Alt-Svc header to pages served out of
> >> >>>> http://users.example.com/~eve announcing an alternative service
> >> >>>> for http://users.example.com on port 23412.  Bob is using an
> >> >>>> Alt-Svc-capable browser.  After Bob has visited
> >> >>>> http://users.example.com/~eve, he visits
> >> >>>> http://users.example.com/~alice.  His browser, obeying Eve's
> >> >>>> Alt-Svc header, accesses the alternative service on port 23412,
> >> >>>> where Eve is running a forward proxy that replaces all pages
> >> >>>> except her own with dancing hamsters.
> >> >>>>
> >> >>>> The original mitigations proposed in the text were "prohibit
> >> >>>> normal users from setting the Alt-Svc header" (which is
> >> >>>> retroactive on pre-Alt-Svc servers) or "prohibit normal users
> >> >>>> from listening for incoming requests" (which is contrary to the
> >> >>>> security model of any shared machine I've used).  This scenario
> >> >>>> originally made me want to require strong auth on any change of
> >> >>>> endpoint, but that breaks the opportunistic security draft.  The
> >> >>>> current text, which I agree does very little, was as strong as we
> >> >>>> could think of a way to make it without breaking the way Opp-Sec
> >> >>>> wanted to work.
> >> >>>>
> >> >>>> I haven't seen such a server since I was in college, so I don't
> >> >>>> know whether they still actually exist and run that way.  I
> >> >>>> presume they do, even if rare, but I have no data.
> >> >>>>
> >> >>>> -----Original Message----- From: Stephen Farrell
> >> >>>> [mailto:stephen.farrell@cs.tcd.ie] Sent: Tuesday, January 12,
> >> >>>> 2016 12:32 PM To: Mike Bishop <Michael.Bishop@microsoft.com>;
> >> >>>> Barry Leiba <barryleiba@computer.org>; Julian Reschke
> >> >>>> <julian.reschke@gmx.de> Cc: draft-ietf-httpbis-alt-svc@ietf.org;
> >> >>>> HTTP Working Group <ietf-http-wg@w3.org> Subject: Re: AD review
> >> >>>> of draft-ietf-httpbis-alt-svc-10
> >> >>>>
> >> >>>>
> >> >>>>
> >> >>>> On 11/01/16 16:45, Stephen Farrell wrote:
> >> >>>>>
> >> >>>>>
> >> >>>>> On 11/01/16 16:34, Mike Bishop wrote:
> >> >>>>>> Haven't heard back from Stephen on the port-change issue we
> >> >>>>>> wanted him to weigh in on; I sent him a reminder.
> >> >>>>>
> >> >>>>> 2nd one worked:-)
> >> >>>>>
> >> >>>>> Lemme go back and read the mail. Please hassle me if I've not
> >> >>>>> gotten back by tomorrow sometime
> >> >>>>
> >> >>>> So as I understand it (thanks Barry), the issue is whether or not
> >> >>>> this text is ok:
> >> >>>>
> >> >>>> "Clients can reduce this risk by imposing stronger requirements
> >> >>>> (e.g. strong authentication) when moving from System Ports to
> >> >>>> User or Dynamic Ports, or from User Ports to Dynamic Ports, as
> >> >>>> defined in Section 6 of [RFC6335]."
> >> >>>>
> >> >>>> FWIW, I have no problem with that. I'm not sure quite what it's
> >> >>>> telling a client to do, but I don't think there's much difference
> >> >>>> these days between lower numbered and higher numbered ports. (If
> >> >>>> that's wrong, I'm sure someone will correct me:-)
> >> >>>>
> >> >>>> Note that I've not read the rest of the document, just that bit.
> >> >>>>
> >> >>>> Cheers, S.
> >> >>>>
> >> >>>>>
> >> >>>>> Cheers, S.
> >> >>>>>
> >> >>>>>>
> >> >>>>>> -----Original Message----- From: barryleiba@gmail.com
> >> >>>>>> [mailto:barryleiba@gmail.com] On Behalf Of Barry Leiba Sent:
> >> >>>>>> Sunday, January 10, 2016 9:20 AM To: Julian Reschke
> >> >>>>>> <julian.reschke@gmx.de> Cc:
> >> >>>>>> draft-ietf-httpbis-alt-svc@ietf.org; HTTP Working Group
> >> >>>>>> <ietf-http-wg@w3.org> Subject: Re: AD review of
> >> >>>>>> draft-ietf-httpbis-alt-svc-10
> >> >>>>>>
> >> >>>>>>>>> I don't think this is a 2119 "MAY": what *else* can it
> >> >>>>>>>>> do?  You have no other guidance about which alternative
> >> >>>>>>>>> alternative to pick, so....  I think this should just
> >> >>>>>>>>> say, "it chooses the most suitable...."
> >> >>>>>>>>
> >> >>>>>>>> Agreed. I haven't changed that yet as it affects
> >> >>>>>>>> normative language but I will unless somebody wants to
> >> >>>>>>>> defend it soonish.
> >> >>>>>>>
> >> >>>>>>> <
> https://github.com/httpwg/http-extensions/commit/a9df1e33703a2cb4
> >> >>>>>>>
> >> >>>>>>>
> >> > 6c
> >> >>>>>>> 9b
> >> >>>>>>>
> >> >>>>>>>
> >> >>>>> 441bfca5bbc04fff80d1>
> >> >>>>>>
> >> >>>>>> Nice.  Is this the last of the updates, or are we still
> >> >>>>>> working on any?  Whenever you're ready to post a new I-D
> >> >>>>>> version, I'll give it a check and request last call.
> >> >>>>>>
> >> >>>>>> Barry
> >> >>>>>>
> >> >>>>>
> >> >>>>>
> >> >>>
> >> >
> >>
> >> --
> >> Mark Nottingham   https://www.mnot.net/
> >>
> >>
> >>
> >>
> >
>
>