Internet DRAFT - draft-rafiee-dnssd-mdns-threatmodel
draft-rafiee-dnssd-mdns-threatmodel
DNSSD H. Rafiee
INTERNET-DRAFT Rozanak
Intended Status: Informational
Expires: November 30, 2015 May 30, 2015
Multicast DNS (mDNS) Threat Model and Security Consideration
<draft-rafiee-dnssd-mdns-threatmodel-03.txt>
Abstract
This document describes threats only specific to extending multicast
DNS (mDNS) across layer 3.
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 November 30, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Threat Analysis . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Human Mistakes . . . . . . . . . . . . . . . . . . . . . 4
3.2. DoS attack . . . . . . . . . . . . . . . . . . . . . . . 4
3.2.1. Large Traffic from mDNS gateway . . . . . . . . . . . 4
3.2.2. Single point of failure . . . . . . . . . . . . . . . 5
3.3. IPv6 specific mDNS scope problems . . . . . . . . . . . . 5
3.4. Malicious update on unicast DNS . . . . . . . . . . . . . 5
3.4.1. mixing unicast names with mDNS names . . . . . . . . 5
3.5. Privacy Problems . . . . . . . . . . . . . . . . . . . . 6
3.5.1. Storing mDNS names in unicast DNS . . . . . . . . . . 6
3.6. Internationalized label and Rogue service . . . . . . . . 6
3.7. Dual stack attacks . . . . . . . . . . . . . . . . . . . 6
3.8. Privacy Protection Mechanisms . . . . . . . . . . . . . . 6
3.8.1. The Use of Random Data . . . . . . . . . . . . . . . 6
3.8.2. Data Encryption . . . . . . . . . . . . . . . . . . . 7
3.9. Evaluation of Security Protection Mechanisms . . . . . . 7
3.9.1. Unicast DNS protection mechanisms . . . . . . . . . . 7
3.9.1.1. DNSSEC . . . . . . . . . . . . . . . . . . . . . 7
3.9.1.2. CGA-TSIG . . . . . . . . . . . . . . . . . . . . 7
3.9.1.3. DNS over DTLS . . . . . . . . . . . . . . . . . . 7
3.9.2. Authorization of a Service Requester . . . . . . . . 7
3.9.2.1. The Use of an Access List . . . . . . . . . . . . 7
3.9.2.2. SAVI-DHCP . . . . . . . . . . . . . . . . . . . . 8
3.9.2.3. The Use of Shared Secret . . . . . . . . . . . . 8
3.9.3. Authorization of a Service . . . . . . . . . . . . . 8
3.9.3.1. SAVI-DHCP . . . . . . . . . . . . . . . . . . . 8
3.9.3.2. Router advertisement . . . . . . . . . . . . . . 8
3.9.4. ULA and GUA Considerations . . . . . . . . . . . . . 9
3.9.4.1. mDNS proxy and Security consideration . . . . . . 9
3.9.5. Other Security Considerations . . . . . . . . . . . . 9
3.10. Not Usable Security Mechanisms . . . . . . . . . . . . 9
3.10.1. IPsec . . . . . . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Multicast DNS (mDNS) was proposed in [RFC6762] to allow nodes in
local links to use DNS-like names for their communication without the
need for global DNS servers, infrastructure and administration
processes for configuration. mDNS along with service discovery
(DNS-SD) [RFC6763] provides nodes with the possibility to discover
other services and the names of other nodes with zero configuration,
i.e., connect a node into a local link and use resources such as a
printer that are available in that network.
mDNS and service discovery (SD) use DNS- like query messages. The
main assumption is that these services also use DNS security
protocols such as DNSSEC. However, it cannot use DNSSEC for security
because DNSSEC is not zero configuration service. Therefore, it
cannot be used for Requirements A, B,C in [requirement]. Besides,
DNSSEC cannot be implemented in all nodes, especially nodes with
limited resources, e.g. 6LoWPAN [RFC4944]. This is why the existing
implementations use no security in local links. This might be not a
critical problem when the service was only advertised in local link
but it is not the same when the service is going to be advertised
over layer 3 and in larger scope. Furthermore, during this step,
DNS-SD did not consider the impact of [RFC4193] that should be
carefully considered when using mDNS to populate DNS. As such, a
Universal Local Address (ULA) prefix is not to be advertised outside
the network domain. This is also similar to the scenario where
address preference rules employed by a proxy device as defined in
section 2.4. [RFC7368].
The purpose of this document is to introduce threat models for
service discovery and allow implementers to be aware of the possible
attacks in order to mitigate them with possible solutions. Since
there are already old lists of known DNS threats available in
[RFC3833], here we only analyze the ones that are applicable to
DNS-SD. We also introduce new possible threats that could result from
extending DNS-SD scope.
2. Terminology
Node: any host and routers in the network
Attack: an action to exploit a node and allow the attacker to gain
access to that node. It can be also an action to prevent a node from
providing a service or using a service on the network
Attacker: a person who uses any node in the network to attack other
nodes using known or unknown threats
Threat: Anything that has a potential to harm a node in the network
Local link vulnerability: Any flaws that are the result of the
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assumption that a malicious node could gain access to legitimate
nodes inside a local link network
Wide Area Network (WAN) vulnerability: Any flaws that are the result
of the assumption that a malicious node could gain access to
legitimate nodes inside any local links in an enterprise network with
multiple Local Area Networks (LANs) or Virtual LANs (VLANs).
Host name: Fully qualified DNS Name (FQDN) of a node in the network
Constrained device: a small device with limited resources (battery,
memory, etc.)
Service advertiser or service: a node that has a service to
advertise, e.g. a printer
Service Requester: a node in the network that requests a service by
the use of DNS-SD protocols. One example of service requester is a
computer that discovers a printer in the network and tries to use it.
3. Threat Analysis
This section only focuses on threats that are specific to
mDNS/DNS-SD. Here we explain them in different example scenarios. The
definition of different use case scenarios are defined in
[requirement].
3.1. Human Mistakes
For those deployments that needs configuration, mis-configuration of
DNS-SD scope on edge devices such as a router or a gateway might
allow an attacker to gain access to services or expose the network
topology to outside of an administrative domains. This is applicable
to all scenarios including PAN, WPAN, home, enterprise, campus, mesh
networks.
3.2. DoS attack
3.2.1. Large Traffic from mDNS gateway
There are several scenarios associated with the Large Traffic
Production case.
First scenario: a malicious node in any of the subnets that the
gateway connects can advertise different fake services or spoof the
information of the real services and replay the messages. This causes
large traffic either in the local link or in other links since the
gateway was also supposed to replicate the traffic to other links.
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Second scenario : a malicious node spoofs the legitimate service
advertisements of different nodes in the network and changes the Time
To Live (TTL) value to zero. This will result in producing large
traffic since the mDNS gateway needs to ask all of the service
advertisers to re-advertise their service. This is an especially
effective attack in a network of constrained devices because it
causes more energy consumption.
Third scenario: a malicious node can spoof the source IP address of a
legitimate victim node and question several services in the link.
This will result in a large traffic return to the victim node from
both gateway and also services.
3.2.2. Single point of failure
a service (like a printer) can overwhelmed with many service
discovery requests from a malicious service requester. This might
result in long waiting times (delay) for a legitimate node to receive
a service.
3.3. IPv6 specific mDNS scope problems
When the ISP, home router/gateway, and a service (like a printer)
support IPv6 addressing, these services may automatically announce
over mDNS both Unique Local Addresses (ULA) [RFC4193] and Global
Unicast Addresses (GUA). Since a GUA is accessible over the internet,
the associated node may become available to the public. The
advertisement needs to be under control to avoid a GUA for a service
becomes known to an attacker. Furthermore, the ULA scope should be
clearly defined so that it does not advertise it to unwanted scope.
This is because it might grant unintended access to a service
otherwise limited by boundaries imposed by mDNS discovery. This
attack is applicable to home, public hotspot, enterprise, campus and
mesh networks.
3.4. Malicious update on unicast DNS
A malicious node can spoof the content of DNS update message and add
malicious records to unicast DNS. This attack is applicable on
enterprise networks.
3.4.1. mixing unicast names with mDNS names
A fake service might poison the cache of a service requester with
records that has global unicast name, if the service requester's
deployment needs configuration and is poorly configured or the
implementation has problem, then the mDNS request might have priority
over DNS request which will lead to phishing attacks.
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3.5. Privacy Problems
If a malicious node is in any subnet (WLAN and WAN) of a network, it
can learn about all services available in this network. The DNS-SD
discloses some critical information about resources in this network
which might be harmful to privacy. This attack is applicable to
temporary public hotspot and enterprise networks.
3.5.1. Storing mDNS names in unicast DNS
When a name of a service is stored in unicast DNS Resource Records,
in case this unicast DNS is accessible over the internet or over
several networks, it might expose the services to unwanted nodes and
harms privacy. This is applicable to campus networks, mesh networks,
temporary public hotspots and enterprise networks.
3.6. Internationalized label and Rogue service
Using Internationalized label might allow an attacker to advertise a
fake service with similar looking character as legitimate service.
This might lead to the case where user chooses fake advertised
service as a legitimate one.
3.7. Dual stack attacks
Having both IPv4 and IPv6 in the same network and trying to aggregate
service discovery traffic on both IP stacks might cause new security
flaws during the translation or aggregation of this traffic. It might
lead to wide range of spoofing attacks or leak service advertisements
(the service advertisement is no longer under control). This attack
is applicable to home, enterprise, campus, mesh and temporary public
hotspots.
3.8. Privacy Protection Mechanisms
3.8.1. The Use of Random Data
Using a random name for services or devices or the use of random
numbers wherever possible, might prevent exposing the exact model or
exact information regarding the DNS-SD service providers (e.g.
printers, etc.) in the network to the attackers. However, this
approach cannot be used for some standard information that the
protocol needs to carry in order to offer service to other nodes.
Otherwise, this random information was exchanged and agreed on
between service providers and service requesters beforehand. This is
exactly against the nature of zero conf protocols, i.e., DNS-SD
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3.8.2. Data Encryption
Encrypting the whole DNS-SD message is another way to hide the
critical information in the network. But this approach might not fit
well to the nature of this protocol. The reason is because these
devices usually respond to anonymous service discovery requests. So,
the attacker can also submit and request the same information. In
other words, encryption in this stage is only extra efforts without
having any benefit from it.
3.9. Evaluation of Security Protection Mechanisms
3.9.1. Unicast DNS protection mechanisms
3.9.1.1. DNSSEC
DNSSEC can be used to allow any services to update its records on
unicast DNS that supports DNSSEC. However, it is not a zero
configuration mechanism and need the introduction of the DNSSEC key
to a service or availability of a trust model. Furthermore, this
mechanism does not provide data confidentiality.
3.9.1.2. CGA-TSIG
CGA-TSIG [cga-tsig] is another possible solution that can provide the
node with secure authentication, data integrity and data
confidentiality. It provides the node with zero or minimal
configuration when it is integrated with SAVI-DHCP or secure RA
message [RFC7113]. This is useful when the node needs to update any
record on an unicast DNS or there is an access list on services. This
approach can be used to authenticate and authorize a node to use a
service or a device.
3.9.1.3. DNS over DTLS
3.9.2. Authorization of a Service Requester
3.9.2.1. The Use of an Access List
There can be an access list on each service with the list of IP
addresses that can use these services. Then the service can use
mechanisms to authorize the service requester or to securely
authenticate them with minimum interaction (zero configuration). This
approach prevents the service from unauthorized use by an attacker.
There are currently some mechanisms available -- SAVI-DHCP, CGA-TSIG,
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etc.
3.9.2.2. SAVI-DHCP
SAVI-DHCP [DHCP-SAVI] approach uses a simple mechanism in switches or
devices that knows information about the ports of switches to filter
any malicious traffic. This mitigates attacks on DHCP server spoofing
and can make sure that nobody can spoof the IP address of the service
providers.
3.9.2.3. The Use of Shared Secret
A shared secret (e.g. a password) can be shared among the service
requesters. Then this value can be used to access the services and
authenticated to them. However, this approach has a disadvantage.
This is because when one of the nodes in this network that carries
this shared secret is compromised then the attacker can also have
unauthorized access to these services. Sharing and re-sharing this
shared secret does not fit to the zero conf nature of DNS-SD
protocol.
3.9.3. Authorization of a Service
It is really important for the service requesters to ensure that the
one claim to be a service (e.g. a printer) is really a service and
its identity has not been forged by the attacker. The service
requester needs to receive the IP address of services in a secure
manner. There are some approaches that can be used for this purpose
such as SAVI-DHCP, Router Advertisement. There are also some
mechanisms that can be used in service requesters to complete this
authentication and authorization processes such as CGA-TSIG, DNS over
TLS
3.9.3.1. SAVI-DHCP
The DHCP server can carry this information and send it to the service
requesters at the same time as the service requesters receive a new
IP address from the DHCP servers.
3.9.3.2. Router advertisement
If Neighbor Discovery Protocol (NDP) [RFC4861] or Secure Neighbor
Discovery (SeND) [RFC3971] are in use, then an option can be added to
a router advertisement message which carries required information
regarding the IP addresses of services. This is especially secure
when SeND is in use. There can be also other protection mechanisms
that is explained in [RFC7113].
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3.9.4. ULA and GUA Considerations
As explained earlier, a ULA prefix is not to be advertised outside
the network domain. Administrators need to clearly set the scope of
the ULAs and configure ACLs on relevant border routers to enforce
this scope. If internal DNS is used, administrators should use
internal-only DNS names for ULAs and perhaps use split horizon DNS to
ensure internal names do not resolve on the Internet as described in
RFC6950.
3.9.4.1. mDNS proxy and Security consideration
Unlike IPv4, there can be multiple IP address assignments per
interface. For example, a printer might return both GUA and ULA. From
a security standpoint, it becomes essential only ULAs be published in
DNS-SD populated by mDNS.
3.9.5. Other Security Considerations
Since a WLAN might also cover a part of city, it is really important
to make sure that there is required filtering in edge networks to
avoid distribution of mDNS/DNS-SD messages beyond the enterprise
networks.
3.10. Not Usable Security Mechanisms
There are some other security mechanisms that are not fit to DNS-SD
protocol but might be useable in future.
3.10.1. IPsec
IPsec is a security protection mechanism. It requires manual step for
the configuration of the nodes. However, recently there are some new
drafts to automate this process. This is, of course, might not be an
ideal solution for DNS-SD. It is because it might not fit to nodes
with limited resources (e.g. battery). Data encryption, as explained
in section 3.12.2. is not suitable for DNS-SD.
4. Security Considerations
This document documents the security of mDNS and DNS-SD. It does not
introduce any additional security considerations
5. IANA Considerations
There is no IANA consideration
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6. Acknowledgements
The author would like to thank all those people who directly helped
in improving this draft, especially John C. Klensin, Douglas Otis,
Dan York and Harald Albrecht
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6762] Cheshire, S., Krochmal, M.,"Multicast DNS", RFC
6762, February 2013
[RFC6763] Cheshire, S., Krochmal, M., "DNS-Based Service
Discovery", RFC 6763, February 2013
[RFC6275] Perkins, C., Johnson, D., Arkko, J., "Mobility
Support in IPv6", RFC 6275, July 2011
[RFC3833] Atkins, D., Austein, R., "Threat Analysis of the
Domain Name System (DNS)", RFC 3833, August 2004
[RFC3971] Arkko, J., Kempf, J., Zill, B., and Nikander, P.,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., Soliman,
H., "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., Culler,
D., "Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
[RFC7113] Gont, F.,"Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113, February 2014.
[RFC4193] Hinden, R., Haberman, B., "Unique Local IPv6
Unicast Addresses", RFC 4193, October 2005
[RFC7368] Chown, T., Arkko, J., Brandt, A., Troan, O.,
Weil, J., "Unique Local IPv6 Unicast Addresses", RFC 7368,
October 2014
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7.2. Informative References
[requirement] Lynn, K., Cheshire, S., Blanchet, M.,
Migault, D., " Requirements for Scalable DNS-SD/mDNS
Extensions",
http://tools.ietf.org/html/draft-ietf-dnssd-requirements-06,
March 2015
[DHCP-SAVI] Bi, J., Wu, J., Yao, G, Baker, F.,"SAVI
Solution for DHCP",
http://tools.ietf.org/html/draft-ietf-savi-dhcp-34,
February 2015
[cga-tsig] Rafiee, H., Loewis, M., Meinel, C.,"Transaction
SIGnature (TSIG) using CGA Algorithm in IPv6",
http://tools.ietf.org/html/draft-rafiee-intarea-cga-tsig ,
June 2014
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Authors' Addresses
Hosnieh Rafiee
http://www.rozanak.com
Munich, Germany
Phone: +49 (0)176 57587575
Email: ietf@rozanak.com
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