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BEHAVE                                                          T. Reddy
Internet-Draft                                         Ram. Ravindranath
Intended status: Informational                            Muthu. Perumal
Expires: September 25, 2014                                        Cisco
                                                                A. Yegin
                                                                 Samsung
                                                          March 24, 2014


               Problems with STUN Authentication for TURN
                    draft-ietf-tram-auth-problems-00

Abstract

   This document discusses some of the issues with STUN authentication
   for TURN messages.

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 25, 2014.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   3
   3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Problems with usage of STUN Authentication  . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The TURN server is a building block to support interactive, real-time
   communication using audio, video, collaboration, games, etc., between
   two peer web browsers using the Web Real-Time communication (WebRTC)
   [I-D.ietf-rtcweb-overview] framework.  The use-case explained in
   "Simple Video Communication Service, enterprise aspects"
   (Section 3.2.5 of [I-D.ietf-rtcweb-use-cases-and-requirements])
   refers to deploying a TURN[RFC5766] server in the DMZ to audit all
   media sessions from inside an Enterprise premises to any external
   peer.  TURN server could also be deployed for RTP Mobility
   [I-D.wing-mmusic-ice-mobility] etc.

   TURN server is also used in the following scenarios:

   o  Users of RTCWEB based web application may use TURN server to hide
      host candidate addresses from the remote peer for privacy.

   o  Enterprise networks deploy firewalls which typically block UDP
      traffic.  When SIP user agents or WebRTC endpoints are deployed
      behind such firewalls, media cannot be sent over UDP across the
      firewall, but must be sent using TCP (which causes a different
      user experience).  In such cases a TURN server deployed in the DMZ
      MAY be used to traverse Firewalls.

   o  TURN Server may be used for IPv4-to-IPv6, IPv6-to-IPv6, and IPv6
      -to-IPv4 relaying [RFC6156].

   o  ICE connectivity checks using server-reflexive candidates could
      fail when the endpoint is behind NAT that performs Address-
      dependent mapping.  In such cases relayed candidate allocated from
      the TURN server is used for media.





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   STUN [RFC5389] specifies an authentication mechanism called the long-
   term credential mechanism.  TURN [RFC5766] in section 4 specifies
   that TURN servers and clients MUST implement this mechanism and the
   TURN server MUST demand that all requests from the client be
   authenticated using this mechanism, or that a equally strong or
   stronger mechanism for client authentication be used.

   In the above scenarios RTCWEB based web applications would use
   Interactive Connectivity Establishment (ICE) protocol [RFC5245] for
   gathering candidates.  ICE agent can use TURN to learn server-
   reflexive and relayed candidates.  If the TURN server requires the
   TURN request to be authenticated then ICE agent will use the long-
   term credential mechanism explained in section 10 of [RFC5389] for
   authentication and message integrity.  TURN specification [RFC5766]
   in section 10 explains the importance of long-term credential
   mechanism to mitigate various attacks.  With proposals
   like[I-D.thomson-mmusic-rtcweb-bw-consent] that defines a STUN
   BANDWIDTH attribute for requesting bandwidth allocation at a TURN
   server, STUN authentication becomes further important to prevent un-
   authorized users from accessing the TURN server and misuse of
   credentials could impose significant cost on the victim TURN server.

   This note focuses on listing the problems with current STUN
   authentication for TURN so that it can serve as the basis for
   stronger authentication mechanisms.

   Compared to a Binding request the Allocate request is more likely to
   be identified by a server administrator as needing client
   authentication and integrity protection of messages exchanged.
   Hence, the issues discussed here in STUN authentication are
   applicable mainly in the context of TURN messages.

2.  Notational Conventions

   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].

   This note uses terminology defined in [RFC5389], [RFC5766].

3.  Scope

   This document can be used as an input to design solution(s) to
   address the problems with the current STUN authentication for TURN
   messages.






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4.  Problems with usage of STUN Authentication

   1.  The long-term credential mechanism in [RFC5389] could use
       traditional "log-in" username and password given to users which
       does not change for extended periods of time and uses the key
       derived from user credentials to generate message integrity for
       every TURN request/response.  An attacker that is capable of
       eavesdropping on a message exchange between a client and server
       can determine the password by trying a number of candidate
       passwords and checking if one of them is correct by calculating
       the message-integrity of the message using these candidate
       passwords and comparing with the message integrity value in the
       MESSAGE-INTEGRITY attribute.

   2.  When TURN server is deployed in DMZ and requires requests to be
       authenticated using the long-term credential mechanism in
       [RFC5389], TURN server needs to be aware of the username and
       password to validate the message integrity of the requests and to
       provide message integrity for responses.  This results in
       management overhead on the TURN server.

   3.  The long-term credential mechanism in [RFC5389] requires that the
       TURN client must include username value in the USERNAME STUN
       attribute.  An adversary snooping the TURN messages between the
       TURN client and server can identify the users involved in the
       call resulting in privacy leakage.  In certain scenarios TURN
       usernames need not be linked to any real usernames given to users
       as they are just provisioned on a per company basis.

   4.  An Attacker posing as a TURN server challenges the client to
       authenticate, learns the USERNAME of the client and later snoops
       the traffic from the client identifying the user activity
       resulting in privacy leakage.

   5.  Hosting multiple realms on a single IP address is challenging
       with TURN.  When a TURN server needs to send the REALM attribute
       in response to an unauthenticated request, it has no useful
       information for determining which realm it should send, except
       the source transport address of the TURN request.  Note this is a
       problem with multi-tenant scenarios only.  This may not be a
       problem when TURN server is located in enterprise premises.

   6.  In WebRTC the Javascript needs be know the username and password
       to use in W3C RTCPeerConnection API to access the TURN server.
       This exposes the user credentials to the Javascript which could
       be malicious.





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5.  Security Considerations

   This document lists problems with current STUN authentication for
   TURN so that it can serve as the basis for stronger authentication
   mechanisms.

6.  IANA Considerations

   This document does not require any action from IANA.

7.  Acknowledgments

   Authors would like to thank Dan Wing, Harald Alvestrand, Sandeep Rao,
   Prashanth Patil, Pal Martinsen and Simon Perreault for their comments
   and review.

8.  References

8.1.  Normative References

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

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.

   [RFC6156]  Camarillo, G., Novo, O., and S. Perreault, "Traversal
              Using Relays around NAT (TURN) Extension for IPv6", RFC
              6156, April 2011.

8.2.  Informative References

   [I-D.ietf-rtcweb-overview]
              Alvestrand, H., "Overview: Real Time Protocols for Brower-
              based Applications", draft-ietf-rtcweb-overview-09 (work
              in progress), February 2014.

   [I-D.ietf-rtcweb-use-cases-and-requirements]
              Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
              Time Communication Use-cases and Requirements", draft-
              ietf-rtcweb-use-cases-and-requirements-14 (work in
              progress), February 2014.




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   [I-D.thomson-mmusic-rtcweb-bw-consent]
              Thomson, M. and B. Aboba, "Bandwidth Constraints for
              Session Traversal Utilities for NAT (STUN)", draft-
              thomson-mmusic-rtcweb-bw-consent-00 (work in progress),
              October 2012.

   [I-D.wing-mmusic-ice-mobility]
              Wing, D., Reddy, T., Patil, P., and P. Martinsen,
              "Mobility with ICE (MICE)", draft-wing-mmusic-ice-
              mobility-06 (work in progress), February 2014.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245, April
              2010.

   [RFC6544]  Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
              "TCP Candidates with Interactive Connectivity
              Establishment (ICE)", RFC 6544, March 2012.

Authors' Addresses

   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: tireddy@cisco.com


   Ram Mohan Ravindranath
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: rmohanr@cisco.com











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   Muthu Arul Mozhi Perumal
   Cisco Systems, Inc.
   Cessna Business Park
   Sarjapur-Marathahalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: mperumal@cisco.com


   Alper Yegin
   Samsung
   Istanbul
   Turkey

   Email: alper.yegin@yegin.org



































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