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Versions: 00

Network Working Group                                        T. Alkemade
Internet-Draft                                          February 9, 2014
Updates: 6120 (if approved)
Intended status: Standards Track
Expires: August 13, 2014


   Validating Info/Query (IQ) stanzas in the Extensible Messaging and
                        Presence Protocol (XMPP)
                  draft-alkemade-xmpp-iq-validation-00

Abstract

   This document provides security recommendations for the validation
   and generation of Info/Query (IQ) stanzas in the Extensible Messaging
   and Presence Protocol (XMPP).  This document updates RFC 6120.

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
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   This Internet-Draft will expire on August 13, 2014.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Discussion Venue  . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 3
     4.1.  No 'from' . . . . . . . . . . . . . . . . . . . . . . . . . 3
     4.2.  Rejecting spoofed replies to queries  . . . . . . . . . . . 4
     4.3.  Preventing presence leaks . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 5






































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1.  Introduction

   The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] uses
   Info/Query (IQ) stanzas as a "request-response" mechanism.  The
   semantics of IQ enable an entity to make a request of, and receive a
   response from, another entity.  The interaction is tracked by the
   requesting entity through use of the 'id' attribute.  Thus, IQ
   interactions follow a common pattern of structured data exchange such
   as get/result or set/result (although an error can be returned in
   reply to a request if appropriate).

   However, it was found not all implementations properly verify the
   origin of IQ responses.  This documents provides recommendations on
   how to avoid spoofed responses.


2.  Terminology

   Various security-related terms are to be understood in the sense
   defined in [RFC4949].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].


3.  Discussion Venue

   The discussion venue for this document is the mailing list of the
   XMPP Working Group, for which archives and subscription information
   can be found at <https://www.ietf.org/mailman/listinfo/xmpp>.


4.  Recommendations

4.1.  No 'from'

   Section 8.1.2.1. of [RFC6120] specifies that IQ stanzas sent on
   behalf of the user's own account MUST either (a) include no 'from'
   attribute or (b) use the user's bare JID as 'from' address (i.e.,
   <localpart@domainpart>).  For compatibility with incorrect servers
   and servers still following [RFC3920], implementations MAY
   additionally accept a reply with either (a) a 'from' address equal to
   the full JID of the client (i.e.,
   <localpart@domainpart/resourcepart>) or (b) a 'from' address equal to
   the domainpart of the JID of the account (i.e., <domainpart>).




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4.2.  Rejecting spoofed replies to queries

   'id' attributes are used as end-to-end identifiers of stanzas: the
   same 'id' attribute is used across every hop.  When delivered, the
   receiver will see the same 'id' value as the sender specified.  As
   described in Section 8.1.3. of [RFC6120], it is REQUIRED to include
   'id' values on IQ stanzas and RECOMMENDED for all other stanza types.
   The entity creating a stanza needs to ensure the 'id' values it
   generates are unique.

   After sending an IQ stanza with type "get" or "set", an entity may
   store the 'id' and 'to' of the outgoing <iq/> element to identify the
   response.  When an IQ stanza comes in with a matching 'id' and type
   "result" or "error", the entity MUST verify that the 'from' attribute
   on the <iq/> matches the 'to' of the outgoing stanza.  If the 'from'
   and 'to' attributes do not match, the entity MUST ignore the stanza.
   As is mandatory in response to IQ stanzas of type "result" or
   "error", the entity MUST NOT return an error.

   For queries where the intended recipient is the server acting on
   behalf of the user's own account entities MAY apply the exceptions in
   Section 4.1.

4.3.  Preventing presence leaks

   Many implementations use a counter to generate new 'id' attributes
   for stanzas to guarantee their uniqueness.  However, this may leak
   presence information of the user: it can give an approximation of how
   long a client has been running and how many stanzas it has sent since
   a previous stanza.  This could, for example, give an indication of
   how many messages a user has sent in a certain time.  Therefore
   clients SHOULD NOT include a counter in the 'id' attribute.

   Additionally, it is RECOMMENDED to use randomly or pseudo-randomly
   generated 'id' attributes.  Implementations using [RFC4122] to
   generate Universally Unique IDentifiers (UUIDs) to use as 'id'
   attributes MUST use version 4 UUIDs, which are randomly or pseudo-
   randomly generated and carry no identifying information.
   Implementations using a pseudo-random generator, either directly or
   for generating UUIDs, SHOULD make sure that future values are hard to
   predict.  For more information see [RFC4086].


5.  IANA Considerations

   This document requests no actions of the IANA.





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6.  Security Considerations

   This document covers security.


7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3920]  Saint-Andre, P., Ed., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              July 2005.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              RFC 4949, August 2007.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.


Author's Address

   Thijs Alkemade

   Email: me@thijsalkema.de



















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