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. 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 September 25, 2014. Copyright Notice Copyright (c) 2014 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Reddy, et al. Expires September 25, 2014 [Page 1] Internet-Draft Problems with STUN Authentication for TURN March 2014 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. Reddy, et al. Expires September 25, 2014 [Page 2] Internet-Draft Problems with STUN Authentication for TURN March 2014 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. Reddy, et al. Expires September 25, 2014 [Page 3] Internet-Draft Problems with STUN Authentication for TURN March 2014 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. Reddy, et al. Expires September 25, 2014 [Page 4] Internet-Draft Problems with STUN Authentication for TURN March 2014 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. Reddy, et al. Expires September 25, 2014 [Page 5] Internet-Draft Problems with STUN Authentication for TURN March 2014 [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 Reddy, et al. Expires September 25, 2014 [Page 6] Internet-Draft Problems with STUN Authentication for TURN March 2014 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 Reddy, et al. Expires September 25, 2014 [Page 7]