[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09

Working Group                                                   A. Barth
Internet-Draft                                             U.C. Berkeley
Expires: July 25, 2009                                        C. Jackson
                                                     Stanford University
                                                              I. Hickson
                                                            Google, Inc.
                                                        January 21, 2009


                         The HTTP Origin Header
                         draft-abarth-origin-00

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 25, 2009.

Copyright Notice

   Copyright (c) 2009 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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.





Barth, et al.             Expires July 25, 2009                 [Page 1]

Internet-Draft           The HTTP Origin Header             January 2009


Abstract

   This document defines the HTTP Origin header.  The Origin header is
   added by the user agent to describe the security context that
   initiated an HTTP request.  HTTP servers can use the Origin header to
   defend themselves against Cross-Site Request Forgery (CSRF) attacks.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Origin . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Comparing Origins  . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Serializing Origins  . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Unicode Serialization of an Origin . . . . . . . . . . . .  6
     4.2.  ASCII Serialization of an Origin . . . . . . . . . . . . .  6
   5.  User Agent Behavior  . . . . . . . . . . . . . . . . . . . . .  8
   6.  HTTP Server Behavior . . . . . . . . . . . . . . . . . . . . .  9
   7.  Privacy Considerations . . . . . . . . . . . . . . . . . . . . 11
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   10. TODO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15




























Barth, et al.             Expires July 25, 2009                 [Page 2]

Internet-Draft           The HTTP Origin Header             January 2009


1.  Introduction

   This document describes the HTTP Origin header.  The Origin header
   identifies the security context that initiated an HTTP request and
   can be used by Web sites to mitigate cross-site request forgery
   (CSRF) vulnerabilities.













































Barth, et al.             Expires July 25, 2009                 [Page 3]

Internet-Draft           The HTTP Origin Header             January 2009


2.  Origin

   The following algoritm MUST be used to compute the origin of a URL.

   1.   Let /url/ be the URL for which the origin is being determined.

   2.   Parse /url/.

   3.   If /url/ does not use a server-based naming authority, or if
        parsing /url/ failed, or if /url/ is not an absolute URL, then
        return an implementation-defined value.

   4.   Let /scheme/ be the scheme component of /url/, converted to
        lowercase.

   5.   If the implementation doesn't support the protocol given by
        /scheme/, then return an implementaion-defined value.

   6.   If /scheme/ is "file", then the implementation MAY return a
        implementation-defined value.

   7.   Let /host/ be the host component of /url/.

   8.   Apply the IDNA ToASCII algorithm to /host/, with both the
        AllowUnassigned and UseSTD3ASCIIRules flags set.  Let /host/ be
        the result of the ToASCII algorithm.

   9.   If ToASCII fails to convert one of the components of the string
        (e.g. because it is too long or because it contains invalid
        characters), then return an implementation-defined value.

   10.  Let /host/ be the result of converting /host/ to lowercase.

   11.  If there is no port component of /url/, then let /port/ be the
        default port for the protocol given by /scheme/.  Otherwise, let
        /port/ be the port component of /url/.

   12.  Return the tuple (/scheme/, /host/, /port/).

   Implementations MAY define other types of origins in addition to the
   scheme/host/port tuple type defined above.  (For example, user agents
   could implement globally unique origins or certificate-based
   origins.)








Barth, et al.             Expires July 25, 2009                 [Page 4]

Internet-Draft           The HTTP Origin Header             January 2009


3.  Comparing Origins

   Implementations MUST use the following algorithm to test whether two
   origins are the "same origin".

   1.  Let /A/ be the first origin being compared, and let B be the
       second origin being compared.

   2.  If either /A/ or /B/ is not a scheme/host/port tuple, return an
       implementation-defined value.

   3.  If /A/ and /B/ have scheme components that are not identical,
       return false.

   4.  If /A/ and /B/ have host components that are not identical,
       return false.

   5.  If /A/ and /B/ have port components that are not identical,
       return false.

   6.  Return true.






























Barth, et al.             Expires July 25, 2009                 [Page 5]

Internet-Draft           The HTTP Origin Header             January 2009


4.  Serializing Origins

4.1.  Unicode Serialization of an Origin

   Implementations MUST using the following algorithm to compute the
   Unicode serialization of an origin:

   1.  If the origin in question is not a scheme/host/port tuple, then
       return the string

          null

       (i.e., the character sequence U+006E, U+0075, U+006C, U+006C) and
       abort these steps.

   2.  Otherwise, let /result/ be the scheme part of the origin tuple.

   3.  Append the string "://" to /result/.

   4.  Apply the IDNA ToUnicode algorithm to each component of the host
       part of the origin tuple, and append the results of each
       component, in the same order, separated by U+002E FULL STOP
       characters (".") to /result/.

   5.  If the port part of the origin tuple gives a port that is
       different from the default port for the protocol given by the
       scheme part of the origin tuple, then append a U+003A COLON
       character (":") and the given port, in base ten, to /result/.

   6.  Return /result/.

4.2.  ASCII Serialization of an Origin

   Implementations MUST using the following algorithm to compute the
   ASCII serialization of an origin:

   1.  If the origin in question is not a scheme/host/port tuple, then
       return the string

          null

       (i.e., the character sequence U+006E, U+0075, U+006C, U+006C) and
       abort these steps.

   2.  Otherwise, let /result/ be the scheme part of the origin tuple.

   3.  Append the string "://" to /result/.




Barth, et al.             Expires July 25, 2009                 [Page 6]

Internet-Draft           The HTTP Origin Header             January 2009


   4.  Apply the IDNA ToASCII algorithm the host part of the origin
       tuple, with both the AllowUnassigned and UseSTD3ASCIIRules flags
       set, and append the result to /result/.

   5.  If ToASCII fails to convert one of the components of the string,
       e.g. because it is too long or because it contains invalid
       characters, then return the literal string "null" and abort these
       steps.

   6.  If the port part of the origin tuple gives a port that is
       different from the default port for the protocol given by the
       scheme part of the origin tuple, then append a U+003A COLON
       character (":") and the given port, in base ten, to /result/.

   7.  Return /result/.




































Barth, et al.             Expires July 25, 2009                 [Page 7]

Internet-Draft           The HTTP Origin Header             January 2009


5.  User Agent Behavior

   Whenever a user agent issues an HTTP request, the user agent MAY
   include an HTTP header named "Origin".

   Whenever a user agent issues an HTTP request whose method is neither
   "GET" nor "HEAD", the user agent MUST include exactly one HTTP header
   named "Origin".

   Whenever a user agent issues an HTTP request that contains an HTTP
   header named "Origin", the value of that header MUST either be

   1.  the string "null" (i.e., the character sequence U+006E, U+0075,
       U+006C, U+006C) or

   2.  the ASCII serialization of the origin that initiated the HTTP
       request.

   Whenever a user agent issues an HTTP request that contains an HTTP
   header named "Origin", if the request was initiated on behalf of an
   origin, the user agent SHOULD use the ASCII serialization of that
   origin as the value of the Origin header.

      Note: This behavior differs from that of the HTTP Referer header,
      which user agents often suppress when an origin with an "https"
      scheme issues a request for a URL with an "http" scheme.

   If a user agent issues an HTTP request in reaction to an HTTP
   redirect, the Origin header MUST contain the same value as the Origin
   header in the HTTP request that generated the redirect.





















Barth, et al.             Expires July 25, 2009                 [Page 8]

Internet-Draft           The HTTP Origin Header             January 2009


6.  HTTP Server Behavior

   HTTP Servers MAY use the Origin header to "defend themselves against
   CSRF attacks."  Such servers are known as "participating servers" in
   this section.

   Let the /origin white list/ of a participating server be a set of
   strings selected by the operator of that server.

   The string "null" MUST NOT be a member of the /origin white list/ for
   any participating server.

      Example: The origin white list for the example.com Web server
      could be the strings "http://example.com", "https://example.com",
      "http://www.example.com", and "https://www.example.com".

   A participating server MUST use the following algorithm when
   determining whether to modify state in response to an HTTP request:

   1.  If the request method is "GET", return "MUST NOT modify state"
       and abort these steps.

   2.  If the request method is "HEAD", return "MUST NOT modify state"
       and abort these steps.

   3.  If the request does not contain a header named "Origin", return
       "MAY modify state" abort these stepts.

   4.  For each request header named "Origin", let /initiating origin/
       be the value of the header:

       1.  If /initiating origin/ is not a member of the /origin white
           list/ for this server, return "MUST NOT modify state" and
           abort these steps.

   5.  Return "MAY modify state".

      Example: A Web server could modify state in response to POST
      requests that lack an Origin header (because these requests are
      sent by non-supporting user agents) and could modify state in
      response to POST requests that have an Origin header of
      "http://example.com", "https://example.com",
      "http://www.example.com", or "https://www.example.com".

   A participating server MUST NOT instruct a user agent to issue an
   HTTP request for a given URL unless the following algorithm returns
   "Safe".




Barth, et al.             Expires July 25, 2009                 [Page 9]

Internet-Draft           The HTTP Origin Header             January 2009


   1.  If the request method is "GET", return "Safe" and abort these
       steps.

   2.  If the request method is "HEAD", return "Safe" and abort these
       steps.

   3.  Let /url/ be the URL in question.

   4.  Let /target origin/ be the origin of /url/.

   5.  If the ASCII serialization of /target origin/ is a member of the
       server's /origin white list/, then return "Safe" and abort these
       steps.

   6.  Return "Unsafe".

      Example: A Web server would be vulnerable to a CSRF attack if it
      responded to an HTTP request with HTML that generated a POST
      request to http://attacker.com/ because the attacker's server
      could respond with an HTTP 307 status and redirect the POST back
      to the original server.






























Barth, et al.             Expires July 25, 2009                [Page 10]

Internet-Draft           The HTTP Origin Header             January 2009


7.  Privacy Considerations

   This section is not normative.

   The Origin header improves on the Referer header by respecting the
   user's privacy: The Origin header includes only the information
   required to identify the principal that initiated the request
   (typically the scheme, host, and port of initiating origin).  In
   particular, the Origin header does not contain the path or query
   portions of the URL included in the Referer header that invade
   privacy without providing additional security.

   The Origin header also improves on the Referer header by NOT leaking
   intranet host names to external Web sites when a user follows a
   hyperlink from an intranet host to an external site because
   hyperlinks generate GET requests.



































Barth, et al.             Expires July 25, 2009                [Page 11]

Internet-Draft           The HTTP Origin Header             January 2009


8.  Security Considerations

   This section is not normative.

   Because a supporting user agent will always include the Origin header
   when making HTTP requests, HTTP servers can detect that a request was
   initiated by a supporting user agent by observing the presence of the
   header.  This design prevents an attacker from making a supporting
   user agent appear to be a non-supporting user agent.  Unlike the
   Referer header, which is absent when suppressed by the user agent,
   the Origin header takes on the value "null" when suppressed by the
   user agent.

   In existing user agents, The Origin header can be spoofed for same-
   site XMLHttpRequests.  Sites that rely only on network connectivity
   for authentication should use a DNS rebinding defense, such as
   validating the HTTP Host header, in addition to CSRF protection.


































Barth, et al.             Expires July 25, 2009                [Page 12]

Internet-Draft           The HTTP Origin Header             January 2009


9.  IANA Considerations

   TODO: The "Origin" header should be registered.
















































Barth, et al.             Expires July 25, 2009                [Page 13]

Internet-Draft           The HTTP Origin Header             January 2009


10.  TODO

   Think about how this interacts with proxies.

   Think about how this interacts with caches.














































Barth, et al.             Expires July 25, 2009                [Page 14]

Internet-Draft           The HTTP Origin Header             January 2009


Authors' Addresses

   Adam Barth
   University of California, Berkeley

   Email: abarth@eecs.berkeley.edu
   URI:   http://www.adambarth.com/


   Collin Jackson
   Stanford University

   Email: collinj@cs.stanford.edu
   URI:   http://www.collinjackson.com/


   Ian Hickson
   Google, Inc.

   Email: ian@hixie.ch
   URI:   http://ln.hixie.ch/






























Barth, et al.             Expires July 25, 2009                [Page 15]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/