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

Re: To cookie or not to cookie

From: Jonas Sicking <jonas@sicking.cc>
Date: Tue, 26 Feb 2008 04:44:32 -0800
Message-ID: <47C409B0.3040706@sicking.cc>
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>

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 

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 Tuesday, 26 February 2008 12:45:12 UTC

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