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Versions: 00 01 02 03 04 05 draft-ietf-httpbis-cookie-prefixes

HTTPbis                                                          M. West
Internet-Draft                                               Google, Inc
Updates: 6265 (if approved)                              October 8, 2015
Intended status: Standards Track
Expires: April 10, 2016


                            Cookie Prefixes
                     draft-west-cookie-prefixes-01

Abstract

   This document updates RFC6265 by adding a set of restrictions upon
   the names which may be used for cookies with specific properties.
   These restrictions enable user agents to smuggle cookie state to the
   server within the confines of the existing "Cookie" request header
   syntax, and limits the ways in which cookies may be abused in a
   conforming user agent.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 10, 2016.

Copyright Notice

   Copyright (c) 2015 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.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and notation  . . . . . . . . . . . . . . . . . .   2
   3.  Prefixes  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  The "$Secure-" prefix . . . . . . . . . . . . . . . . . .   3
     3.2.  The "$Origin-" prefix . . . . . . . . . . . . . . . . . .   3
   4.  User Agent Requirements . . . . . . . . . . . . . . . . . . .   4
   5.  Aesthetic Considerations  . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Section 8.5 and Section 8.6 of [RFC6265] spell out some of the
   drawbacks of cookies' implementation: due to historical accident, it
   is impossible for a server to have confidence that a cookie set in a
   secure way (e.g., as a domain cookie with the "Secure" (and possibly
   "HttpOnly") flags set) remains intact and untouched by non-secure
   subdomains.

   We can't alter the syntax of the "Cookie" request header, as that
   would likely break a number of implementations.  This rules out
   sending a cookie's flags along with the cookie directly, but we can
   smuggle information along with the cookie if we reserve certain name
   prefixes for cookies with certain properties.

   This document describes such a scheme, which enables servers to set
   cookies which conforming user agents will ensure are "Secure", and
   locked to a domain.

2.  Terminology and notation

   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].

   The "scheme" component of a URI is defined in Section 3 of [RFC3986].








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3.  Prefixes

3.1.  The "$Secure-" prefix

   If a cookie's name begins with "$Secure-", the cookie MUST be set
   with a "Secure" attribute.

   The following cookie would be rejected:

   Set-Cookie: $Secure-SID=12345; Domain=example.com

   While the following would be accepted:

   Set-Cookie: $Secure-SID=12345; Secure; Domain=example.com

3.2.  The "$Origin-" prefix

   If a cookie's name begins with "$Origin-", the cookie MUST be:

   1.  Sent only to hosts which are identical to the host which set the
       cookie.  That is, a cookie named "$Origin-cookie1" set from
       "https://example.com" MUST NOT contain a "Domain" attribute (and
       will therefore sent only to "example.com", and not to
       "subdomain.example.com").

   2.  Sent to every request for a host.  That is, a cookie named
       "$Origin-cookie1" MUST contain a "Path" attribute with a value of
       "/".

   3.  Sent only to secure origins, if set from a secure origin.  That
       is, a cookie named "$Origin-cookie1" set from
       "https://example.com" MUST contain a "Secure" attribute, as it
       was set from a URI whose "scheme" is considered "secure" by the
       user agent.

   The following cookies would always be rejected:

   Set-Cookie: $Origin-SID=12345
   Set-Cookie: $Origin-SID=12345; Secure
   Set-Cookie: $Origin-SID=12345; Domain=example.com
   Set-Cookie: $Origin-SID=12345; Secure; Domain=example.com

   The following would be rejected, if set from a secure origin, but
   accepted if set from a non-secure origin:

   Set-Cookie: $Origin-SID=12345; Path=/

   While the following would be accepted, if set from a secure origin:



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   Set-Cookie: $Origin-SID=12345; Secure; Path=/

4.  User Agent Requirements

   This document updates Section 5.3 of [RFC6265] as follows:

   After step 10 of the current algorithm, the cookies flags are set.
   Insert the following steps to perform the prefix checks this document
   specifies:

   1.  If the "cookie-name" begins with the string "$Origin-", then:

       1.  If the "scheme" component of the "request-uri" denotes a
           "secure" protocol (as determined by the user agent), and the
           cookie's "secure-only-flag" is "false", abort these steps and
           ignore the cookie entirely.

       2.  If the cookie's "host-only-flag" is "false", abort these
           steps and ignore the cookie entirely.

       3.  If the cookie's "path" is not "/", abort these steps and
           ignore the cookie entirely.

   2.  If the "cookie-name" begins with the string "$Secure-", and the
       cookie's "secure-only-flag" is "false", abort these steps and
       ignore the cookie entirely.

5.  Aesthetic Considerations

   Prefixes are ugly. :(

6.  Security Considerations

   This scheme gives no assurance to the server that the restrictions on
   cookie names are enforced.  Servers could certainly probe the user
   agent's functionality to determine support, or sniff based on the
   "User-Agent" request header, if such assurances were deemed
   necessary.

7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.






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   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              DOI 10.17487/RFC6265, April 2011,
              <http://www.rfc-editor.org/info/rfc6265>.

Appendix A.  Acknowledgements

   Eric Lawrence had this idea a million years ago.  Devdatta Akhawe
   helped justify the potential impact of the scheme on real-world
   websites.

Author's Address

   Mike West
   Google, Inc

   Email: mkwst@google.com
   URI:   https://mikewest.org/





























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