Internet DRAFT - draft-ietf-tram-auth-problems
draft-ietf-tram-auth-problems
TRAM T. Reddy
Internet-Draft R. Ravindranath
Intended status: Informational Cisco
Expires: February 19, 2015 M. Perumal
Ericsson
A. Yegin
Samsung
August 18, 2014
Problems with STUN long-term Authentication for TURN
draft-ietf-tram-auth-problems-05
Abstract
This document discusses some of the security and practical problems
with the current Session Traversal Utilities for NAT (STUN)
authentication for Traversal Using Relays around NAT (TURN) messages.
Status of This Memo
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This Internet-Draft will expire on February 19, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Problems with STUN long-term Authentication for TURN . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Traversal Using Relays around NAT (TURN) [RFC5766] is a protocol that
is often used to improve the connectivity of Peer-to-Peer (P2P)
applications (as defined in section 2.7 of [RFC5128]). TURN allows a
connection to be established when one or both sides is incapable of a
direct P2P connection. The TURN server is also 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.
TURN server is also used in the following scenarios:
o Users of WebRTC 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
DeMilitarized Zone (DMZ) might be used to traverse firewalls.
o 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 server in the DMZ to audit all media sessions from inside
an Enterprise premises to any external peer.
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o TURN server could also be deployed for RTP Mobility
[I-D.wing-tram-turn-mobility] etc.
o TURN Server may be used for IPv4-to-IPv6, IPv6-to-IPv6, and IPv6 -
to-IPv4 relaying [RFC6156].
o Interactive Connectivity Establishment (ICE) [RFC5245]
connectivity checks using server reflexive candidates could fail
when the endpoint is behind NAT [RFC3235] that performs Address-
dependent mapping as described in section 4.1 of [RFC4787]. In
such cases relayed candidate allocated from the TURN server is
used for media.
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 applications would use ICE protocol 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, client authentication is
essential 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 security and practical problems with
current STUN authentication for TURN so that it can serve as the
basis for stronger authentication mechanisms.
An Allocate request is more likely than a Binding request 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
This note uses terminology defined in [RFC5389], [RFC5766].
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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 STUN long-term Authentication for TURN
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 the 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. Long-term credentials
(username, realm, and password) need to be stored on the server-
side using MD5 hash over the credentials, which is not considered
best current practice. [RFC6151] discusses security
vulnerabilities of MD5 and encourages not to use it. It is not
possible to use STUN long-term credentials in US FIPS 140-2
[FIPS-140-2] compliant implementations, since MD5 isn't an
approved algorithm.
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. If TURN usernames are linked
to real usernames then it will result in privacy leakage, but 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. STUN authentication relies on HMAC-SHA1 [RFC2104]. There is no
mechanism for hash agility in the protocol itself, although
Section 16.3 of [RFC5389] does discuss a plan for migrating to a
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more secure algorithm in case HMAC-SHA1 is found to be
compromised.
5. A man-in-the middle 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.
6. 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 in the
response, 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.
7. In WebRTC the Javascript code needs to 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. The malicious java script could misuse
or leak the credentials. If the credentials happen to be used
for accessing services other than TURN then the security
implications are much larger.
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, Marc Petit-Huguenin, Gonzalo
Camarillo, Brian E Carpenter, Spencer Dawkins, Adrian Farrel and
Simon Perreault for their comments and review.
8. References
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8.1. Normative References
[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
[FIPS-140-2]
NIST, , "NIST, "Security Requirements for Cryptographic
Modules"", June 2005,
<http://csrc.nist.gov/publications/fips/fips140-2/
fips1402.pdf>.
[I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-10
(work in progress), June 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.
[I-D.wing-tram-turn-mobility]
Wing, D., Patil, P., Reddy, T., and P. Martinsen,
"Mobility with TURN", draft-wing-tram-turn-mobility-00
(work in progress), June 2014.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC3235] Senie, D., "Network Address Translator (NAT)-Friendly
Application Design Guidelines", RFC 3235, January 2002.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
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[RFC5128] Srisuresh, P., Ford, B., and D. Kegel, "State of Peer-to-
Peer (P2P) Communication across Network Address
Translators (NATs)", RFC 5128, March 2008.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, April
2010.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, March 2011.
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
Muthu Arul Mozhi Perumal
Ericsson
Ferns Icon
Doddanekundi, Mahadevapura
Bangalore, Karnataka 560037
India
Email: muthu.arul@gmail.com
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Alper Yegin
Samsung
Istanbul
Turkey
Email: alper.yegin@yegin.org
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