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From "Jason Smith (JIRA)" <>
Subject [jira] [Commented] (COUCHDB-431) Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
Date Sat, 17 Sep 2011 17:04:08 GMT


Jason Smith commented on COUCHDB-431:

CORS bugs allow cross-site request forgery (XSRF) attacks--the most dangerous threat on the

IMHO, to say "CORS is not about security" is to disqualify one from making an implementation.

CORS is a three-body problem:

1. Client = browser
2. Server = couch
3. Origin = site the browser is on, a tuple {protocol, hostname, port}, e.g.

The word "sharing" sounds nice and friendly. It reminds me of kindergarten. That word is misleading.

Attention Couch developers and administrators: and every other site on the
Web is, even now, attacking your couch, fetching and storing data, and they have ALL OF YOUR
USERS' session cookies. does this by attracting visitors to their site, and sending Javascript to
the browsers to perform their attacks for them. Your ONLY protection is that browsers will
not (generally) query to a different domain. With CORS, browsers will query, but only if the
couch tells them it is okay. We are seriously playing with fire here.

Databases are not characters in this story. Per-database CORS settings
make as much sense as per-database user accounts. Practically, syncing _security objects between
multiple databases will be a complete nightmare. And, it presents a race condition where cross-origin
policies are incorrect between DB create and _security updates.) But  what about /_session?
How come can access /origins_db/ but once your session times out, it can't
reconnect? How come it can't fetch some /_uuids?

> Support cross domain XMLHttpRequest (XHR) calls by implementing Access Control spec
> -----------------------------------------------------------------------------------
>                 Key: COUCHDB-431
>                 URL:
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: HTTP Interface
>    Affects Versions: 0.9
>            Reporter: James Burke
>            Assignee: Benoit Chesneau
>            Priority: Minor
>             Fix For: 1.2
>         Attachments: 0001-cors-support.-should-fix-COUCHDB-431-2.patch, 0001-cors-support.-should-fix-COUCHDB-431.patch,
0001-cors-support.-should-fix-COUCHDB-431.patch, 0001-cors-support.-should-fix-COUCHDB-431.patch,
0001-cors-support.-should-fix-COUCHDB-431.patch, A_0001-Generalize-computing-the-appropriate-headers-for-any.patch,
A_0002-Send-server-headers-for-externals-responses.patch, A_0003-Usably-correct-w3c-CORS-headers-for-valid-requests.patch,
A_0004-Respond-to-CORS-preflight-checks-HTTP-OPTIONS.patch, cors.html, cors_test.html, test_cors2-1.tgz,
> Historically, browsers have been restricted to making XMLHttpRequests (XHRs) to the same
origin (domain) as the web page making the request. However, the latest browsers now support
cross-domain requests by implementing the Access Control spec from the W3C:
> In order to keep older servers safe that assume browsers only do same-domain requests,
the Access Control spec requires the server to opt-in to allow cross domain requests by the
use of special HTTP headers and supporting some "pre-flight" HTTP calls.
> Why should CouchDB support this: in larger, high traffic site, it is common to serve
the static UI files from a separate, differently scaled server complex than the data access/API
server layer. Also, there are some API services that are meant to be centrally hosted, but
allow API consumers to use the API from different domains. In these cases, the UI in the browser
would need to do cross domain requests to access CouchDB servers that act as the API/data
access server layer.
> JSONP is not enough in these cases since it is limited to GET requests, so no POSTing
or PUTing of documents.
> Some information from Firefox's perspective (functionality available as of Firefox 3.5):
> And information on Safari/Webkit (functionality in latest WebKit and Safari 4):
> IE 8 also uses the Access Control spec, but the requests have to go through their XDomainRequest
object (XDR):
> and I thought IE8 only allowed GET or POST requests through their XDR.
> But as far as CouchDB is concerned, implementing the Access Control headers should be
enough, and hopefully IE 9 will allow normal xdomain requests via XHR.

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