W3C home > Mailing lists > Public > public-appformats@w3.org > February 2008

Access Control Spec and Cookies

From: Arthur Barstow <art.barstow@nokia.com>
Date: Fri, 29 Feb 2008 16:24:32 -0500
Message-Id: <ABC34A90-81C5-4B04-B65A-E0DCB7E857B3@nokia.com>
To: Maciej Stachowiak <mjs@apple.com>, Adele Peterson <adele@apple.com>, Marc Silbey <marcsil@microsoft.com>, Doug Stamper <dstamper@microsoft.com>, Anne van Kesteren <annevk@opera.com>, public-appformats@w3.org

Browser Vendors, Maciej, Adele, Marc, Doug, Anne,

There has been a rather lengthy discussion regarding the Access  
Control for Cross-site Requests spec and Cookies, starting with this  
thread from Jonas:

  <http://www.w3.org/mid/47BE7A2A.8040605@sicking.cc>

Due to concerns about exposing a user's cookies, Mozilla decided they  
will not send cookies in this model:

  <http://www.w3.org/mid/47C409B0.3040706@sicking.cc>

We are all very interested in other browser vendors' position on this  
issue. Would you please share your view on this?

Regards, Art Barstow
---


Begin forwarded message:

> Resent-From: public-appformats@w3.org
> From: "ext Jonas Sicking" <jonas@sicking.cc>
> Date: February 26, 2008 7:44:32 AM EST
> To: Anne van Kesteren <annevk@opera.com>
> Cc: Brad Porter <bwporter@yahoo.com>, Daniel Veditz  
> <dveditz@mozilla.com>, "WAF WG (public)" <public- 
> appformats@w3.org>, Window Snyder <window@mozilla.com>, Brandon  
> Sterne <bsterne@mozilla.com>, Jesse Ruderman <jruderman@gmail.com>
> Subject: Re: To cookie or not to cookie
> Archived-At: <http://www.w3.org/mid/47C409B0.3040706@sicking.cc>
>
>
> Anne van Kesteren wrote:
>> I'd like to see an update on this from the Mozilla folks. I think  
>> if cookies are not part of the request we should simply nuke the  
>> whole idea.
>
> So we had another (and hopefully final :) ) security meeting at  
> mozilla today. I'll post a separate mail about the other issues  
> that came up as the only really big thing is the cookie issue.
>
> So the prevailing opinion was that sending cookies without getting  
> the users consent is simply too easy to misunderstand. A server  
> that sends private data based on cookie information and include a  
> rule like
>
> allow <linkedin.com>
>
> has essentially just sent all the private data served on that URI  
> over to linkedin, without getting the users consent. And of course  
> this becomes many times worse if the rule is allow <*>. At that  
> point basically any private data for anyone to read.
>
> While it can definitely be argued that the server should ask the  
> users consent first, just as it does before selling personal data  
> to other 3rd parties this seems like a much easier mistake to make.  
> Sending all your users personal information to a 3rd party like  
> linkedin requires an active action. Just adding a header to your  
> responses in order to allow mashups requires much less thinking.
>
> There are three parties involved in this transaction. The user, the  
> requesting site and the target site. The spec clearly enforces that  
> the latter two parties are ok with this transaction. But asking the  
> user is left as a responsibility to the target site.
>
> Unfortunately we are not convinced that all sites will get this  
> right. Especially given the ease at which this spec can be deployed.
>
> So we have decided that we do not want to include cookies in the  
> request.
>
> So at this point there are a few ways forward:
>
> 1. We can leave the spec as is and say that mozilla is intentionally
>    only implementing a subset of the spec at this point.
>
> I'm not at all exited about this idea. It very much increases the  
> risk that server administrators will wrongly configure their  
> servers such that private user data will be wrongly exposed if  
> another UA implements access-control and do send cookies. This  
> includes both other browsers, and later versions of firefox.
>
> If it comes to this we will likely simply drop support for access- 
> control for firefox 3 in order to not hinder deployment by other  
> vendors of the full spec.
>
> 2. We can change the spec to say that cookies should never be sent.
>
> This would support the very common usecase of the data hosted on  
> the target site not being personal at all. Such as the ability to  
> fetch the latest ads on craigslist.org, or fetch the directions to  
> a destination from google maps.
>
> But I'm not exited about this idea as sending cookies and auth  
> headers does have several security advantages when fetching private  
> data. Such as never having to expose any credentials to the  
> requesting site, and having built-in protection against distributed  
> dictionary attacks. Something that won't be possible if the  
> credentials have to be included in the request body.
>
> 3. We can change the spec to allow for requests both that include
>    cookies, and requests that don't include them. We'd further say
>    that before the UA makes a request that do include cookies it
>    should get the users permission to do so first.
>
> This would support the very common usecase of the data hosted on  
> the target site not being personal at all. Such as the ability to  
> fetch the latest ads on craigslist.org, or fetch the directions to  
> a destination from google maps.
>
> I think this could be a very interesting option, if done right. The  
> "how to ask the user for permission" part is tricky, but I think  
> doable. And it's something that the spec wouldn't have to work out  
> in detail, but can be left up to the UA.
>
> The issue of how to determine if the request should be done with or  
> without cookies is something we would need to specify though. One  
> solution would be to say that unless the UA has any prior knowledge  
> (from for example a previous session), it should first make a  
> request that does not include cookies. If that request is denied  
> the UA should ask the user and then, if granted permission, do a  
> request that includes cookies.
>
> This is very similar to how http authentication is usually done.
>
>
> Do note that I'm prepared to go with any of the above three  
> options. If we really don't want to change the spec we are  
> perfectly happy with holding off on this feature for a future  
> firefox release.
>
> If we go with 3, note that for the next firefox release we would  
> then act as if the user always denies the request to send cookies.  
> Implementing UI to ask the user is not going to happen for this  
> release. Nothing would prevent it from happening next release though.
>
>
>> One thing that might be worth considering is adopting the policy  
>> Safari and Internet Explorer have for cookies. That is not  
>> accepting third-party cookies, but always including cookies in the  
>> request. Then again, there are already tracking methods without  
>> cookies and are actively being used (Hixie pointed out paypal +  
>> doubleclick on IRC) so I'm not sure whether complicated cookie  
>> processing models are worth it at all.
>
> That wouldn't actually change anything at all. The major concern is  
> sites sending replies that contain the users private data to GET  
> requests that include cookies. This will happen even if the reply  
> can't set additional cookies.
>
> The third-party-cookie blocker thing is mostly there to (poorly)  
> stop sites from tracking a user across multiple sites.
>
>
> I realize a lot of people are probably going to be disappointed  
> with this decision, me included. But I hope we can find a way  
> forward that minimizes the disappointment, even if that includes  
> removing support for any of this from the next firefox release.
>
> / Jonas
>
Received on Friday, 29 February 2008 21:25:54 GMT

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