Network Working Group C. Vogt
Internet-Draft Universitaet Karlsruhe (TH)
Expires: January 24, 2007 J. Kempf
DoCoMo USA Labs
July 23, 2006
Security Threats to Network-Based Localized Mobility Management
draft-ietf-netlmm-threats-02.txt
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Abstract
This document discusses security threats to network-based localized
mobility management. Threats may occur on two interfaces: the
interface between an LMA and a MAG, as well as the interface between
a MAG and a mobile node. Threats to the former interface impact the
localized mobility management protocol itself.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Threats to Interface between LMA and MAG . . . . . . . . . . . 4
2.1 LMA Compromise or Impersonation . . . . . . . . . . . . . 4
2.2 MAG Compromise or Impersonation . . . . . . . . . . . . . 5
2.3 Man in the Middle Attack . . . . . . . . . . . . . . . . . 6
2.4 Denial of Service Attack on the LMA . . . . . . . . . . . 7
3. Threats to Interface between MAG and Mobile Node . . . . . . . 7
3.1 Network Access Identity . . . . . . . . . . . . . . . . . 8
3.2 Impersonation of Mobile Nodes . . . . . . . . . . . . . . 8
3.3 Man in the Middle Attack . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Informative References . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
A. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . 14
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1. Introduction
The network-based localized mobility management (NETLMM) architecture
[1] supports movement of IPv6 mobile nodes locally within a domain
without requiring mobility support in the mobile nodes' network
stacks. A mobile node can keep its IP address constant as it moves
from link to link, avoiding the signaling overhead and latency
associated with changing the IP address. While software specifically
for localized mobility management is not required on the mobile node,
IP-layer movement detection software may be necessary, and driver
software for link-layer mobility is prerequisite.
The IP addresses of mobile nodes have a prefix that routes to a
localized mobility anchor (LMA). This LMA maintains an individual
route for each mobile node. Any particular mobile node's route
terminates at a mobile access gateway (MAG) which the mobile node
uses as a default router on its current access link. MAGs are
responsible for updating the mobile node's route on the LMA as the
mobile node moves. The localized mobility management architecture
therefore has two interfaces:
1. The interface between MAGs and the LMA where route update
signaling occurs.
2. The interface between mobile nodes and their currently selected
MAGs where link-layer handoff signaling and possibly IP-layer
movement detection signaling occurs.
The localized mobility management architecture specifies no
standardized protocol for a MAG to detect the arrival or departure of
mobile nodes on its local link and initiate route update signaling
with the LMA. An appropriate mechanism may be entirely implemented
at the link layer, such as is common for cellular networks. In that
case, the IP layer never detects any movement, even when a mobile
node moves from one link to another handled by a different MAG. If
the link layer does not provide the necessary functionality, the
mobile node must perform active IP-layer movement detection signaling
so as to trigger route update signaling at the MAG.
This document discusses security threats on both interfaces of
localized mobility management. The discussion is limited to threats
specific to localized mobility management; threats to IPv6 in general
are documented in [2].
1.1 Terminology
The terminology in this document follows the definitions in [3], with
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those revisions and additions from [1]. In addition, the following
definition is used:
Network access identity
An identity established for the mobile node during network access
authentication that allows the network to unambiguously identify
the mobile node for signaling purposes. The network access
identity may, e.g., be bound to a link-layer session key, a
network access identifier (NAI) [4], or a SEND public key [5].
2. Threats to Interface between LMA and MAG
The localized mobility management protocol executed on the interface
between the LMA and a MAG serves to establish, update, and tear down
routes for data plane traffic of mobile nodes. Threats to this
interface can be separated into compromise or impersonation of a
legitimate LMA, compromise or impersonation of a legitimate MAG, man-
in-the-middle attacks, and denial-of-service attacks on the LMA.
2.1 LMA Compromise or Impersonation
A compromised LMA can ignore routing updates from a legitimate MAG,
or forge routing updates for a victim mobile node in order to
redirect or deny the mobile node's traffic. Since data plane traffic
for all mobile nodes routes through the LMA, a compromised LMA can
also intercept, inspect, modify, redirect, or drop such traffic on a
MAG supported by the LMA. The attack can be conducted transiently,
to selectively disable traffic for any particular mobile node or MAG
at particular times.
Moreover, a compromised LMA may manipulate its routing table such
that all packets are directed towards a single MAG. This may result
in a DoS attack against that MAG and its attached link.
These threats also emanate from an attacker which tricks a MAG into
believing that it is the legitimate LMA. This attacker can cause the
MAG to conduct route update signaling with the attacker instead of
with the legitimate LMA, enabling it to ignore route updates from the
MAG, or forge route updates in order to redirect or deny a victim
mobile node's traffic. The attacker does not necessarily have to be
on the original control plane path between the legitimate LMA and the
MAG, provided that it can somehow make its presence known to the MAG.
E.g., the IP address of a mobility anchor point in hierarchical
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Mobile IPv6 mobility management [6] may be proliferated across a
domain hop by hop in Router Advertisement messages. Failure to
properly authenticate a comparable mechanism for localized mobility
management would allow an attacker to establish itself as a rouge
LMA.
The attacker may further be able to intercept, inspect, modify,
redirect, or drop data plane traffic to and from a mobile node. This
is obvious if the attacker is on the original data plane path between
the legitimate LMA and the mobile node's current MAG, which may
happen independent of whether or not the attacker is on the original
control plane path. If the attacker is not on this path, it may be
able to leverage the localized mobility management protocol to
redefine the prefix that the mobile node uses in IP address
configuration. The attacker can then specify a prefix that routes to
itself. Whether or not outgoing data plane packets sourced by the
mobile node can be interfered with by an attacker off the original
data plane path depends on the specific data plane forwarding
mechanism within the localized mobility management domain. E.g., if
IP-in-IP encapsulation or an equivalent per-mobile-node approach is
used for outbound data plane packets, the packets will route through
the attacker. On the other hand, standard IP routing may cause the
packets to be relayed via the legitimate LMA and hence to circumvent
the attacker.
2.2 MAG Compromise or Impersonation
A compromised MAG can redirect a victim mobile node's traffic onto
its local access link arbitrarily, without authorization from the
mobile node. This threat is similar to an attack on a typical
routing protocol where a malicious stub router injects a bogus host
route for the mobile node. In general, forgery of a subnet prefix in
link state or distance vector routing protocols requires support of
multiple routers in order to obtain a meaningful change in forwarding
behavior. But a bogus host route is likely to take precedence over
the routing information advertised by legitimate routers, which is
usually less specific, hence the attack should succeed even if the
attacker is not supported by other routers. A difference between
redirection in a routing protocol and redirection in localized
mobility management is that the former impacts the routing tables of
multiple routers, whereas the latter involves only the compromised
MAG and the LMA.
A compromised MAG can further ignore the presence of a mobile node on
its local access link and refrain from registering the mobile node at
the LMA. The mobile node then loses its traffic. Attacks that the
MAG can mount on its access link interface are common for any regular
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IPv6 access router [2].
Moreover, a compromised MAG may be able to cause interruption to a
mobile node by deregistering the mobile node at the LMA, pretending
that the mobile node has powered down. The mobile node then needs to
reinitiate the network access authentication procedure, which the
compromised MAG may prevent repeatedly until the mobile node moves to
a different MAG. The mobile node should be able to handle this
situation, but the recovery process may be lengthy and hence impair
ongoing communication sessions to a significant extent.
All of these threats apply not just to a MAG that is compromised, but
also to an attacker that manages to counterfeit the identity of an
authorized MAG in interacting with both mobile nodes and the LMA.
Such an attacker can behave towards mobile nodes like a legitimate
MAG and engage the LMA in route update signaling. The attack may be
conducted transiently, to selectively disable traffic for any
particular mobile node at particular times.
2.3 Man in the Middle Attack
An attacker that manages to interject itself between the legitimate
LMA and a legitimate MAG can act as a man in the middle with respect
to both control plane signaling and data plane traffic. If the
attacker is on the original control plane path, it can forge, modify,
or drop route update packets so as to cause the establishment of
incorrect routes or the removal of routes that are in active use.
Similarly, an attacker on the original data plane path can intercept,
inspect, modify, redirect, and drop data plane packets sourced by or
destined to a victim mobile node.
A compromised router located between the LMA and a MAG may cause
similar damage. Any router on the control plane path can forge,
modify, or drop control plane packets, and thereby interfere with
route establishment. Any router on the data plane path can
intercept, inspect, modify, and drop data plane packets, or rewrite
their IP headers so as to divert the packets from their original
path.
An attacker between the LMA and a MAG may further impersonate the MAG
towards the LMA and vice versa in route update signaling. The
attacker can so interfere with route establishment even if it is not
on the original control plane path between the LMA and the MAG. An
attacker off the original data plane path may undertake the same to
cause inbound data plane packets destined to the mobile node to be
routed first from the LMA to the attacker, and from there to the
mobile node's MAG and finally to the mobile node itself. As
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explained in Section 2.1, here, too, it depends on the specific data
plane forwarding mechanism within the localized mobility management
domain whether or not the attacker can influence the route of
outgoing data plane packets sourced by the mobile node.
2.4 Denial of Service Attack on the LMA
An attacker may launch a denial-of-service attack on the LMA by
sending packets to arbitrary IP addresses which are potentially in
use by mobile nodes within the localized mobility management domain.
Like a border router, the LMA is in a topological position through
which all data plane traffic goes, so it must process the flooding
packets and perform a routing table lookup for each of them. The LMA
can discard packets for which the IP destination address is not
registered in the routing table. But other packets must be
encapsulated and forwarded. A target MAG as well as any mobile nodes
attached to its access link are also likely to suffer damage because
the unrequested packets must be decapsulated and consume link
bandwidth as well as processing capacities on the receivers. This
threat is in principle the same as for denial of service on a regular
IPv6 border router, but because either the routing table lookup
enables the LMA to drop a flooding packet early or, on the contrary,
additional tunneling workload is required, the impact of an attack
against localized mobility management may be different.
In a related attack, the villain manages to obtain a globally
routable IP address of an LMA or a different network entity within
the localized mobility management domain and perpetrates a denial-of-
service attack against that IP address. Localized mobility
management is in general somewhat resistant to such an attack because
mobile nodes need never obtain a globally routable IP address of any
entity within the localized mobility management domain. A
compromised mobile node hence cannot pass such an IP address off to a
remote attacker, limiting the feasibility of extracting information
on the topology of the localized mobility management domain. It is
still possible for an attacker to perform IP address scanning if MAGs
and LMAs have globally routable IP addresses, but the much larger
IPv6 address space makes scanning considerably more time consuming.
3. Threats to Interface between MAG and Mobile Node
In order to detect the arrival and departure of mobile nodes and
accordingly initiate route updates with the LMA, a MAG monitors the
mobile nodes' link-layer handoff signaling or IP-layer movement
detection signaling. Cellular access technologies utilize only the
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signaling at the wireless link layer, and the IP stack never sees any
change when the mobile node moves from one MAG to a MAG on a
different link. For non-cellular access technologies, such as IEEE
802.11 or wired Ethernet, the link-layer signaling may not hide a
handoff from the IP layer. Instead, IP-layer movement detection
signaling may have to be performed in response to a notification from
the link layer that a change in link-layer attachment has occurred.
This signaling may involve extensions [7] for IPv6 Neighbor Discovery
[8], DHCPv6 [9], or additional technology-specific functionality at
the IP layer. In any case, the security threats on the interface
between the MAG and a mobile node are the same. They either pertain
to impersonation of the mobile node or to man-in-the-middle attacks.
3.1 Network Access Identity
In order for localized mobility management to be able to definitively
and unambiguously identify a mobile node upon handoff, the mobile
node must establish a network access identity when it initially
connects to the localized mobility managment domain. E.g., the
mobile node may authenticate itself to the domain based on its NAI
[4] and an AAA-based protocol. The network access identity is
conceptually independent of the mobile node's IP or link-layer
addresses. For some wireless access technologies, the network access
identity must be re-established on every link-layer handoff.
Localized mobility management requires the establishment of a secure
binding between the network access identity and either the IP
addresses of the mobile node, or any authentication keys associated
with these IP addresses. The binding is used by the MAG to deduce
that the mobile node has handed over onto the MAG's access link,
thereby providing the trigger for route update signaling to the LMA.
The binding must be robust to spoofing because it would otherwise
facilitate impersonation of the mobile node by a third party or man-
in-the-middle attacks.
3.2 Impersonation of Mobile Nodes
An attacker that is able to forge the network access identity of a
neighboring victim mobile node can trick its MAG into redirecting the
mobile node's packets to itself. Such an on-link attack is common
for any regular IPv6 network [2].
However, if handoff signaling cannot definitively be linked back to
the legitimate network access identity, an attacker may be capable of
fabricating handoff signaling of a victim mobile node that currently
attaches to a different link. The attacker can thus trick its MAG
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into believing that the mobile node has handed over onto the MAG's
access link. The MAG will then initiate route update signaling to
the LMA, causing the LMA to redirect inbound data plane packets for
the mobile node to the attacker's MAG and finally to the attacker
itself. The attacker can so examine the packets that legitimately
belong to the mobile node, or discard the packets and deny the mobile
node service. This is conceivable both if the attacker and the
mobile node are on links that connect to different MAGs, as well as
if they are on separate links connecting to the same MAG. In the
former case, two MAGs would think they see the mobile node and both
would independently perform route update signaling with the LMA. In
the latter case, route update signaling is likely to be performed
only once, and the redirection of packets from the mobile node to the
attacker is internal to the MAG. The mobile node can always
recapture its traffic back from the attacker through another run of
link-layer handoff signaling and/or IP-layer movement detection
signaling. But standard mobile nodes are generally not prepared to
counteract this kind of attack, and even where network stacks include
suitable functionality, the attack may not be noticeable early enough
at the link or IP layer to quickly institute countermeasures. The
attack is therefore disruptive at a minimum, and may potentially
persist until the mobile node initiates signaling again upon a
subsequent handoff.
Off-link impersonation attacks can be prevented at the link layer.
E.g., they are not possible with cellular access technologies, where
the handoff signaling is completely controlled by the wireless link
layer. Here, an attacker must be on the same link as the victim
mobile node in order to disrupt the negotiation between the mobile
node and the network. Cellular access technologies also provide
other cryptographic and non-cryptographic attack barriers at the link
layer, which make mounting an impersonation attack, both on-link and
off-link, very difficult. For non-cellular access technologies,
however, off-link impersonation attacks may be possible.
3.3 Man in the Middle Attack
An attacker which can interpose between a victim mobile node and the
MAG during link-layer handoff signaling and/or IP-layer signaling for
movement detection, router discovery, and IP address configuration
can mount a man-in-the-middle attack on the mobile node, spoofing the
mobile node into believing that it has a legitimate connection with
the localized mobility management domain. The attacker can thus
intercept, inspect, modify, or selectively drop packets sourced by or
destined to the mobile node.
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4. Security Considerations
This document describes threats to network-based localized mobility
management. These may either occur on the interface between the LMA
and a MAG, or on the interface between a MAG and a mobile node.
Mitigation measures for the threats, as well as the security
considerations associated with those measures, are described in the
respective protocol specifications [10][11] for the two interfaces.
5. IANA Considerations
This document has no actions for IANA.
6. Acknowledgment
The authors would like to thank the NETLMM working group, especially
Jari Arkko, Gregory Daley, Gerardo Giaretta, Wassim Haddad, Julien
Laganier, Lakshminath Dondeti, Henrik Levkowetz, Phil Roberts, Vidya
Narayanan, and Pekka Savola (in alphabetical order) for valuable
comments and suggestions regarding this document.
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7. Informative References
[1] Kempf, J., "Problem Statement for Network-based Localized
Mobility Management", IETF Internet Draft
draft-ietf-netlmm-nohost-ps-04.txt (work in progress),
June 2006.
[2] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", IETF Request for
Comments 3756, May 2004.
[3] Manner, J. and M. Kojo, "Mobility Related Terminology",
IETF Request for Comments 3753, June 2004.
[4] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network
Access Identifier", IETF Request for Comments 4282,
December 2005.
[5] Aura, T., "Cryptographically Generated Addresses (CGA)",
IETF Request for Comments 3972, March 2005.
[6] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier,
"Hierarchical Mobile IPv6 Mobility Management (HMIPv6)",
IETF Request for Comments 4140, August 2005.
[7] Kempf, J., Narayanan, S., Nordmark, E., Pentland, B., and JH.
Choi, "Detecting Network Attachment in IPv6 Networks (DNAv6)",
IETF Internet Draft draft-ietf-dna-protocol-01.txt (work in
progress), June 2006.
[8] Narten, T., "Neighbor Discovery for IP version 6 (IPv6)",
IETF Internet Draft draft-ietf-ipv6-2461bis-07.txt (work in
progress), May 2006.
[9] Droms, R., Bound, J., Volz, B., Lemon, T., E., C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", IETF Request for Comments 3315, July 2003.
[10] Giaretta, G., "NetLMM Protocol", IETF Internet Draft
draft-giaretta-netlmm-dt-protocol-00.txt (work in progress),
June 2006.
[11] Laganier, J., Narayanan, S., and F. Templin, "Network-based
Localized Mobility Management Interface between Mobile Node and
Access Router", IETF Internet Draft
draft-ietf-netlmm-mn-ar-if-01.txt (work in progress),
June 2006.
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Authors' Addresses
Christian Vogt
Institute of Telematics
Universitaet Karlsruhe (TH)
P.O. Box 6980
76128 Karlsruhe
Germany
Email: chvogt@tm.uka.de
James Kempf
DoCoMo USA Labs
181 Metro Drive, Suite 300
San Jose, CA 95110
USA
Phone: +1 408 451 4711
Email: kempf@docomolabs-usa.com
Appendix A. Change Log
The following is a list of technical changes that were made from
version 01 to version 02 of the document. Editorial revisions are
not explicitly identified.
o Section 2.1: Included DoS/flooding attack against MAG. Also
clarified how a malicious node off the control plane path between
the authorized LMA and one or multiple target MAGs could
impersonate the authorized LMA against the MAGs. Such an attacker
could use various means to interfer with data plane traffic even
if it is off the original data plane path between the legitimate
LMA and the MAGs.
o Section 2.2: Malicious MAG may deregister an actively
communicating mobile node, without consent of the mobile node.
o Section 2.3: Included related threats pertaining to MITM between
LMA and MAG, which were formerly described in other sections.
o Section 2.4: Included description of DoS/flooding attack against
LMA, including its impact on the target MAGs, their links, and the
target mobile nodes.
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o Section 3: Revised the structure of this section. Threats are
now divided into attacks against a mobile node's network access
identity; impersonation of a mobile node, both from the mobile
node's link and from off link; as well as man-in-the-middle
attacks.
o Section 3.1: The binding with the network access identity may be
with the authentication keys associated with the mobile node's IP
address, not necessarily with the IP addresses themselves.
o Section 3.2: Off-link attack may be mounted from a link that
connects to a different MAG than the victim mobile node's MAG.
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