Internet DRAFT - draft-reddy-behave-turn-auth
draft-reddy-behave-turn-auth
BEHAVE T. Reddy
Internet-Draft Ram. Ravindranath
Intended status: Standards Track Muthu. Perumal
Expires: April 03, 2014 Cisco
A. Yegin
Samsung
September 30, 2013
Problems with STUN Authentication for TURN
draft-reddy-behave-turn-auth-04
Abstract
This document discusses some of the issues with STUN authentication
for TURN messages.
Status of This Memo
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This Internet-Draft will expire on April 03, 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 . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
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.
4. Problems with usage of STUN Authentication
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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.
5. Security Considerations
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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-08 (work
in progress), September 2013.
[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-11 (work in
progress), June 2013.
[I-D.thomson-mmusic-rtcweb-bw-consent]
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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-05 (work in progress), September 2013.
[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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