Internet DRAFT - draft-nir-websec-extended-origin
draft-nir-websec-extended-origin
Network Working Group Y. Nir, Ed.
Internet-Draft Check Point
Updates: 6454 (if approved) March 6, 2012
Intended status: Standards Track
Expires: September 7, 2012
A More Granular Web Origin Concept
draft-nir-websec-extended-origin-02
Abstract
This document defines an HTTP header that allows the partitioning of
a single origin (as defined in RFC 6454) into multiple origins, so
that the same origin policy applies among them.
The header introduced in this document allows a portal to specify
that resources that appear to be from the same origin should, in
fact, be treated as though they are from different origins, by
extending the 3-tuple of the origin to a 4-tuple. A compliant user
agent is expected to apply the same-origin policy according to the
4-tuple rather than the 3-tuple.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 7, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . . 3
2. The Extended-Origin Header . . . . . . . . . . . . . . . . . . 3
2.1. Header Format . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Update to the Serialization Requirements . . . . . . . . . 4
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Determining the Extended Origin based on a URL . . . . . . . . 6
5. CORS interaction . . . . . . . . . . . . . . . . . . . . . . . 7
6. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Other Methods of Encoding Server Identity . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
10. Changes from Previous Versions . . . . . . . . . . . . . . . . 8
10.1. Changes in version -02 . . . . . . . . . . . . . . . . . . 8
10.2. Changes in version -01 . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
Reverse proxies such as SSL VPN portals "flatten" part of the Web, by
providing access to multiple web sites through a single host. For
example, a company portal may be located at
https://sslvpn.example.com, and allow remote access to several
websites that form the corporate intranet as well as webified access
to the mail server. The different services are distinguised by
implementation-specific manipulation of the URL. For example, the
following three URLs may be respectively for the internal mail
server, for the internal wiki, and for Wikipedia:
1. https://sslvpn.example.com/link/my_web_mail/inbox/index.html
2. https://sslvpn.example.com/link/the_wiki/index.html
3. https://sslvpn.example.com/ext/wikipedia.org
The problem here is that although there are separate servers, they
all map to the same origin as defined in [RFC6454]. Scripts from any
of these sites can affect others. In fact, the Origin header as
defined in section 7 of RFC 6454 can leak information to the real web
server that it is located within the same flattened domain.
The HTTP header introduced in this document allows the portal to
specify that URLs that appear to be from the same origin are, in
fact, from different origins, by extending the 3-tuple of the origin
to a 4-tuple. The user agent would be expected to apply the same-
origin policy according to the 4-tuple rather than the 3-tuple.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. The Extended-Origin Header
When a web portal hides multiple actual web sites behind its own
origin, it MUST add the new Extended-Origin header defined in the
next section. The name field need not be related to the actual web
origin, and is not meant for human consumption. The requirement is
only that different origins MUST have different names in the header.
If the response from the original web site already contains one or
more Extended-Origin headers, then the portal adds its own header
after the rest.
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2.1. Header Format
The ABNF is to be added.
The header includes a name, which is not necessarily meant for human
consumption, and a path parameter. The general format is
Extended-Origin: name; path=/something
This means that all requests of the format "GET /something/..." will
be considered as going to the origin defined by the combination of
the RFC 6454 origin and the name. As such, cookies from the portal
MUST not be returned in requests to the extended origin, and vice
versa. Scripts from inside the extended origin MUST be prevented
from executing requests against the main portal and against other
extended origins within the same portal.
2.2. Update to the Serialization Requirements
Section 6 of RFC 6454 defines how to serialize an origin for
inclusion in the "Origin" header defined in section 7 of that RFC.
For serializing an extended origin, follow steps 1-3 of section 6.1
or 6.2 of RFC 6454. To the result, append the name from the
Extended-Origin header and a U+002E FULL STOP code points (".").
Then continue with steps 4-6.
For example, if the host is sslvpn.example.com, and the name in the
extended origin header is webmail, then the serialized origin becomes
https://webmail.sslvpn.example.com
To avoid collisions between serialized extended origins and
serialized non-extended origins, servers SHOULD NOT use readable
origins such as "webmail". Instead they should choose random-looking
extended origin names, possibly obtained by hashing an internally
meaningful name.
3. Examples
Here's an example of a connection with both the Extended-Origin and
the Origin headers.
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CONNECT https://sslvpn.example.com
GET / HTTP/1.1
HTTP/1.1 200 OK
Content-Type: application/octet-stream
Set-Cookie: session=1234
<html>
<body>
Welcome, you can read your mail
<a href="/link/my_web_mail/inbox/index.html">here</a>
</body>
</html>
GET /link/my_web_mail/inbox/index.html HTTP/1.1
Referer: https://sslvpn.example.com/
Cookie: session=1234
HTTP/1.1 200 OK
Content-Type: application/octet-stream
Extended-Origin: d41d8cd98f00b204; path=/link/my_web_mail
Set-Cookie: mailsession=5678
<html>
<body>
You have 1 unread message. Jumping in 5 seconds...
<script>...</script>
</body>
</html>
GET /link/my_web_mail/inbox/msg0945.html HTTP/1.1
Referer: https://sslvpn.example.com/link/my_web_mail/inbox/index.htm
Origin: https://d41d8cd98f00b204.sslvpn.example.com
Cookie: mailsession=5678
In this example, the first GET was the result of the user typing in
an address, or following a link. Therefore it has no Origin header.
It goes to the main page of the portal, so the response contains no
Extended-Origin.
The second GET also happened because of clicking a link, not by any
action of the page, so there's no need to send an Origin header. If
there had been such a header, it would be just as defined in RFC
6454: https://sslvpn.example.com
The third GET is caused by a script running on the mail page. This
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page came with an Extended-Origin header, and so the user agent
constructs the Origin header in the request according to the new
rules in Section 2.2.
Note that the cookie set by the main portal was not sent in the third
request. The second reply marked all requests beginning with "/link/
my_web_mail" as belonging to the extended origin, and the third
request matches that pattern. Cookies from the non-extended origin
are not forwarded to the extended origin.
The second request did include the portal cookie in a request to the
mail server. This is only an issue with the main portal cookies, not
among the extended origins. Some SSL VPN portals strip their own
cookies from requests going to the other servers, and this behavior
is RECOMMENDED.
4. Determining the Extended Origin based on a URL
This section defines an algorithm for converting a URL into an
origin. This section is not normative, and compliant browsers may
implement this in other ways.
For each visited site, the browser keeps a table mapping paths to
origin names. Initially, this table looks like this:
+------+------+
| Path | Name |
+------+------+
| / | |
+------+------+
Table 1: Initial table
As Extended-Origin headers are encountered, entries are added to the
table. For example, after seeing the header in the example in
Section 3, the table will look like this:
+-------------------+------------------+
| Path | Name |
+-------------------+------------------+
| / | |
| /link/my_web_mail | d41d8cd98f00b204 |
| /link/SAP | 12c30f3bb3275376 |
+-------------------+------------------+
Table 2: The table with 2 more entries
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When presented with a URL, the browser can normally figure the
scheme, host and port. The name parameter can be figured out form
the path according to the closes match in the table. Here are some
URLs and the origins to which they map:
+------------------------------------+------------------------------+
| URL | Extended Origin |
+------------------------------------+------------------------------+
| https://sslvpn.example.com/index.h | https://sslvpn.example.com |
| tml | |
| https://sslvpn.example.com/link/my | https://d41d8cd98f00b204.ssl |
| _web_mail/msg0005.html | vpn.example.com |
| https://sslvpn.example.com/link/SA | https://sslvpn.example.com |
| PIENCE/index.html | |
| https://sslvpn.example.com/link/SA | https://12c30f3bb3275376.ssl |
| P/index.html | vpn.checkpoint.com |
| https://sslvpn.example.com/ext/wik | https://sslvpn.example.com |
| ipedia.org/index.html | |
+------------------------------------+------------------------------+
Table 3: Extended origin examples
5. CORS interaction
The interaction between this draft and CORS ([CORS]) is to be added.
6. Open Issues
6.1. Other Methods of Encoding Server Identity
Some SSL-VPN products and configurations do not encode the server
identity using a prefix in the URL, as shown in the example in
Section 3. One such Method is this:
https://sslvpn.example.com/p/inb/msg0945.html,HOST=mail.example.com
The issue here is that the way the path parameter is defined, you
cannot use it to define what URLs belong to the extended origin. We
could replace it with a parameter that accepts a regular expression,
but that seems overly complex:
Extended-Origin: webmail; expr=/p/*,HOST=mail.example.com
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7. Acknowledgements
Oren Souroujon contributed some of the text in this document, and
also came up with the original idea. Yehezkel Horowitz helped with
reviewing the draft and pointing out the issues with cookies and
paths.
Thanks to James Manger and Tobias Gondrom for reviewing the first
version of this draft.
8. Security Considerations
This document causes compliant clients to disallow certain actions
that are allowed today. In that sense, it reduces the attack
surface.
More to be added.
9. IANA Considerations
The permanent message header field registry (see [RFC3864]) should be
updated with the following registration:
o Header field name: Extended-Origin
o Applicable protocol: http
o Status: Standard
o Author/Change controller: IETF
o Specification document: this specification
10. Changes from Previous Versions
NOTE TO RFC EDITOR: Please remove this section before publication.
10.1. Changes in version -02
Added Section 4 about converting URLs to extended origins
10.2. Changes in version -01
Removed the special handling of portals behind portals.
Changed the syntax of the serialized origin from fragment-like to
subdomain-like.
Cleaned up some grammar.
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11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
December 2011.
11.2. Informative References
[CORS] van Kesteren, A., "Cross-Origin Resource Sharing", W3C
Working Draft WD-cors-20100727, July 2010.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", RFC 3864, BCP 90,
September 2004.
Author's Address
Yoav Nir (editor)
Check Point Software Technologies Ltd.
5 Hasolelim st.
Tel Aviv 67897
Israel
Email: ynir@checkpoint.com
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