IETF Mobile IP Working Group T. Aura
INTERNET DRAFT Microsoft
Expires August 2002 J. Arkko
Ericsson
February 2002
MIPv6 BU Attacks and Defenses
draft-aura-mipv6-bu-attacks-01.txt
Status of This Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF),
its areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document overviews attacks against mobile and fixed IP nodes
by exploiting features of the Mobile IPv6 Route Optimization. Many
of the attacks can be prevented by authenticating the Mobile IPv6
Binding Updates (BU) but some cannot, some depend on the details of
the BU protocol, and some denial-of-service attacks specifically
take advantage of authentication mechanisms. The purpose of this
document is to help those involved in the design and
standardization of BU authentication protocols to understand the
attacks, to assess suggested protection mechanisms, and to choose
between different levels of protection.
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Table of Contents
Status of This Memo...............................................1
Abstract..........................................................1
Table of Contents.................................................2
1. Introduction...................................................3
2. Attacks that Corrupt Routing Tables............................3
2.1 Spoofing Binding Updates (o).................................4
2.2 Attacks against Secrecy and Integrity (o)....................5
2.3 Basic Denial of Service Attacks (o)..........................5
2.4 Replaying and Blocking Binding Updates (o)...................6
2.5 Bombing CoA with Unwanted Data...............................6
2.6 Bombing HoA with unwanted data (*)...........................8
3. Authentication of Binding Updates..............................8
3.1 Public Key Authentication (o)................................9
3.2 Cryptographically Generated Addresses........................9
3.3 Return Routability for HoA and CoA (*)......................10
3.4 Assuming a safe route.......................................12
3.5 Two Independent Routes......................................13
3.6 Leap of Faith...............................................14
3.7 The Role of Ingress Filtering (o)...........................14
4. DoS Attacks against BU Authentication.........................15
4.1 Inducing Unnecessary Binding Updates........................15
4.2 Consuming Authentication Resources..........................16
4.3 Forcing Non-Optimized Routing (o)...........................17
4.4 Reflection and Amplification (*)............................17
5. Preventing Resource Exhaustion................................18
5.1 Delaying Commitment.........................................18
5.2 Controlling Damage..........................................20
5.3 Favoring Regular Customers..................................20
6. The Right Level of Protection.................................21
6.1 Prioritizing the Goals (*)..................................21
6.2 Multiple Levels of Authentication (*).......................22
7. Security Considerations.......................................24
8. Conclusions...................................................25
Acknowledgments..................................................25
References.......................................................25
Authors' Addresses............................................27
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1. Introduction
This document describes attacks against Mobile IPv6 [JP01] Route
Optimization and related protection mechanisms. The goal of the
attacker can be to corrupt the correspondent host's routing table
(the Binding Cache) and to cause packets to be routed to a wrong
address. This can compromise secrecy and integrity of communication
and cause denial-of-service (DoS) both at the communicating parties
and at the address that receives the unwanted packets. The attacker
may also exploit features of a Binding Update (BU) protocol to
exhaust the resources of either the mobile or the correspondent.
The aim of this document is to describe the major attacks and to
overview various protocol mechanisms and their limitations.
In particular, we want to make known several attacks which should
be considered when designing a protocol for authenticating BUs but
which have only lately received attention at the Working Group
(e.g. they were not mentioned in [MPH+01]). First, data flows can
be redirected to flood a third party who is not taking part in the
BU protocol (Sec. 2.5 -2.6 ). Second, some proposed BU
authentication protocols can be broken by attackers located on the
route from the correspondent to the Home Agent (Sec. 3.5 ). Third,
an attacker can consume the resources of any mobile or
correspondent by inducing authentic but unnecessary Binding Updates
(Sec. 4.1 ).
It is essential to understand that some of the threats are more
serious than others, some can be mitigated but not removed, and
some may be acceptable or too expensive to prevent. There are also
various security mechanisms that provide different levels of
guarantees for different security properties. We are particularly
interested in mechanisms that allow authentication between
arbitrary Internet nodes without pre-established trust
relationships, public-key infrastructure (PKI), or trusted third
parties (TTP). This means that some compromises must be made. The
question for the protocol designer is, which design choices give an
acceptable level of protection at an acceptable cost. Our goal is
to help answering this question.
We have marked with (o) the sections that contain only well-known
material, which most readers are likely to be familiar with but
which is included for completeness. Sections with major changes or
additions since the previous version have been marked with a star
(*).
2. Attacks that Corrupt Routing Tables
Route optimization and Binding Updates create a new opportunity for
attackers. By sending false BUs, they can create false entries in
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the correspondent host's Binding Cache and, thus, reroute IP
packets to wrong destinations. If the data in the packets is not
protected cryptographically, this can lead to compromise of secrecy
and integrity. The attacker may also cause denial-of-service by
keeping data from arriving at the right destination and by bombing
a target host or network with unwanted data.
We consider only active attackers. The rationale behind this is
that in order to corrupt a routing table, the attacker must sooner
or later send one or more messages. Thus, it makes little sense to
consider attackers that only observe messages but do not send any.
In fact, the active attacks are easier to for the average attacker
than passive ones would be. In most active attacks, the attacker
can initiate the BU protocol execution at any time while more
passive attacks would require the attacker to wait for suitable
messages to be sent by the targets hosts.
2.1 Spoofing Binding Updates (o)
If Binding Updates are not authenticated, an attacker can send
spoofed BUs. All Internet hosts are vulnerable to this attack
because they all must support the correspondent functionality.
There is also no way of telling which addresses belong to mobile
hosts that really could send BUs. Consider an IP host A sending IP
packets to another IP host B. The attacker can redirect the packets
to an arbitrary address C by sending to A a Binding Update where
the home address (HoA) is B and the care-of address (CoA) is C.
After receiving this BU, A will send all packets intended for B to
the address C.
The attacker may select the CoA to be either its own current
address (or another address in its local network) or any other IP
address. If the attacker selects a local CoA where it can receive
packets, it will be able to send further packets to a
correspondent, which the correspondent believes to be coming from
the mobile. Ingress filtering at the attacker's local network does
not prevent the spoofing of Binding Updates but forces the attacker
either to choose a CoA from inside its own network or to use the
Alternate CoA sub-option. This may make it easier for the attack
targets to selectively filter the spurious BUs at a firewall.
The correspondent stores the HoA-CoA pair in its Binding Cache. The
attacker needs to send a new BU every few minutes to refresh the
cache entry.
The attacker needs to know or guess the IP addresses of both the
sender and receiver. This means that it is difficult to redirect
all packets to or from a host because the attacker would need to
know the IP addresses of all the hosts with which it is
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communicating. Hosts with well-known addresses, such as servers and
those using stateless auto-configuration, are most vulnerable.
Hosts that are a part of the network infrastructure, such as DNS
servers, are particularly interesting targets for attackers.
Hosts with frequently changing random addresses and no DNS names
are relatively safe. However, hosts that visit publicly accessible
networks such as airport wireless LANs risk revealing their
addresses. IPv6 addressing privacy features [ND01] mitigate these
risks to an extent but it should be noted that addresses cannot be
completely recycled while there are still open sessions that use
those addresses.
2.2 Attacks against Secrecy and Integrity (o)
By spoofing Binding Updates, an attacker can redirect packets
between two IP hosts to itself. By sending a spoofed BU to A, it
can capture the data intended to B. It can pretend to be B and
highjack B's connections with A, or establish new spoofed
connections. The attacker can also send spoofed BUs to both A and B
and insert itself to the middle of all connections between them
(man-in-the-middle attack). Consequently, the attacker is able to
see and modify the packets sent between A and B. The attacks are
possible if the target host or its correspondent supports Route
Optimization and the attacker knows their IP addresses.
Strong encryption and integrity protection, such as authenticated
IPSec, can prevent all the attacks against data secrecy and
integrity. When the data is cryptographically protected, spoofed
BUs can result in denial of service but not in disclosure or
corruption of sensitive data beyond revealing the existence of the
traffic flows. Two fixed hosts could also protect communication
between themselves by refusing to accept BUs from each other.
Ingress filtering, on the other hand, does not help because the
attacker is using its own address as the CoA and is not spoofing
source IP addresses.
The attacks described above are a serious threat to the Internet
for two reasons. First, a lot of Internet traffic is unprotected.
Second, an attacker anywhere on the network can mount the attacks
against any Internet hosts, also non-mobile ones. If Binding
Updates did not exist, the attacker would need to be on the route
between the attack targets in order to listen to the traffic
between them.
2.3 Basic Denial of Service Attacks (o)
By sending spoofed BUs, the attacker can redirect all packets sent
between two IP hosts to a random or nonexistent address. This way,
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it may be able to stop or disrupt communication between the hosts.
The requirements are that the target host or its correspondent must
support Route Optimization and the attacker must know their IP
addresses.
The attack is serious because any Internet host can be targeted,
also fixed hosts. Hosts belonging to the infrastructure necessary
for other hosts to communicate are also vulnerable. Again, two
hosts can protect the communication between themselves by refusing
BUs from each other or by establishing an authenticated IPSec
tunnel for the BUs.
2.4 Replaying and Blocking Binding Updates (o)
Any protocol for authenticating BUs will have to consider replay
attacks. That is, an attacker may be able to replay recent
authenticated BUs to the correspondent and, that way, direct
packets to the mobile host's previous location. Like spoofed BUs,
this can be used both for capturing packets and for DoS. The
attacker can capture the packets and impersonate the mobile node if
it reserves the mobile's previous address after the mobile has
moved away and then replays the previous BU to redirect packets
back to the previous location.
The replays are a concern if a timestamps are used for checking the
freshness of BUs and the mobile is moving so frequently that it
sends the next BU before the timestamp in the previous BU has
expired. Sequence numbers in authenticated BUs usually prevent the
attack. The authentication protocol needs to be is carefully
designed to avoid more complex replay attacks.
In a related attack, the attacker blocks binding updates from the
mobile at its new location, e.g. by jamming the radio link or by
mounting a flooding attack, and takes over its connections at the
old location. The attacker will be able to capture the packets sent
to the mobile and to impersonate the mobile until the
correspondent's Binding Cache entry expires.
Both of the above attacks require the attacker to be on the same
local network with the mobile, where it can relatively easily
observe packets and block them even if the mobile does not move to
a new location. Therefore, we believe that these attacks are not as
serious as ones that can be mounted from remote locations.
2.5 Bombing CoA with Unwanted Data
By sending spoofed BUs, the attacker can redirect traffic to an
arbitrary IP address. This can be used to bomb an arbitrary
Internet address with excessive amounts of data. The attacker can
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also target a network by redirecting data to one or more IP
addresses within the network.
In the simplest attack, the attacker knows that there is a heavy
data stream from host A to B and redirects this to the target
address C. A will soon stop sending the data because it is not
receiving acknowledgments from B.
A more sophisticated attacker acts itself as B. It first subscribes
to a data stream (e.g. a video stream from a news web site) and
then redirects this to the target address C. The attacker may even
be able to spoof the acknowledgements. For example, consider a
constant-rate TCP stream. The attacker performs the TCP handshake
itself and thus knows the initial sequence numbers. After
redirecting the data to C, it suffices to send one spoofed
acknowledgment per window. In a constant-rate stream, the attacker
is able to predict the sequence numbers, the window size, and the
right times for sending the acknowledgments. This way, the attacker
is able to redirect a steady stream of unwanted data to the target
address without doing much work itself. It can carry on opening
more streams and refresh the Binding Cache entries by sending a new
BU every few minutes.
(TCP provides some protection against this attack: If C is the
address of a real host, it will respond with TCP Reset, which
should prompt A to close the connection. On the other hand, if C is
a non-existent address, A will receive both the spoofed
acknowledgments and ICMP Destination Unreachable messages.
Depending on the implementation, A may ignore the error messages.
Other transport-layer protocols might behave less gracefully.)
The attack is serious because the target can be any host or
network, not only mobile one. What makes it particularly serious
compared to the other attacks is that the target itself cannot do
anything to prevent the attack. For example, it does not help if
the target network stops using Route Optimization. The damage is
the worst if these techniques are used to amplify the effect of a
distributed denial of service (DDoS) attack. Ingress filtering in
the attacker's local network prevents the spoofing of source
addresses but the attack is still possible by setting the Alternate
CoA sub-option to the target address.
The attacker needs to find a correspondent that is willing to send
data streams to unauthenticated recipients. Many popular web sites
provide such streams. If the target is a single host, the attacker
needs to know or guess the target's IP address. On the other hand,
if the target is an entire network, the attacker can congest the
link toward that network by bombing random addresses within its
routing prefix or group of prefixes. In some cases, a firewall on
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the border of the target network may be able filter out data that
is sent to nonexistent addresses. Whether this is possible depends
on the way that the addresses within that network are managed. It
seems likely that IPv6 addressing privacy features would preclude
such filtering in the general case.
2.6 Bombing HoA with unwanted data (*)
A variation of the bombing attack targets the HoA instead of the
CoA. The attacker claims to be a mobile with the HoA equal to the
target address. It starts downloading a data stream. The attacker
then sends a BU cancellation (i.e. a request to delete the binding
from the Binding Cache), or allows the cache entry to expire, which
redirects the data stream to the HoA. Just like when bombing the
CoA, the attacker can keep the stream alive by spoofing
acknowledgments.
When BUs are not authenticated, the attacker can choose an
arbitrary address as the HoA and thus target any Internet node. BU
authentication usually limits the attacker's choice of target
address but care must be taken when designing the protocol. For
example, one draft protocol verified the correctness of HoA (using
a return routability test, see Sec. 3.3 ) only when a Binding Cache
entry was created. This would allow the attacker to target any
network where it has once owned an address, e.g. a public access
LAN. A limit on the Binding Cache entry lifetimes or more frequent
verification of HoA virtually prevents the attacks.
When successful, the bombing attack against HoA is just as serious
as the one against CoA. One mechanism is not usually enough to
prevent both types of bombing attacks and they should be considered
separately when designing a BU authentication protocol.
3. Authentication of Binding Updates
In order to prevent the corruption of correspondent routing tables,
the Binding Updates must be authenticated. The two first
subsections (Sec. 3.1 -3.2 ) discuss relatively strong, public-key
authentication methods. The later subsections go into progressively
weaker authentication methods that would be labeled as insecure in
the traditional black-and-white network security thinking.
Nevertheless, some of them (Sec. 3.3 -3.4 ) do provide well-defined
levels of assurance in the real networks and can complement or even
replace the stronger methods. The motivation is that instead of
trying to prevent all attacks, the best strategy is often to limit
the number of potential attackers that can attack a particular
target, and to reduce the number of targets a potential attacker
can threaten. In particular, limiting the number of attackers is
essential in defending against denial-of-service attacks on the
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Internet because it is rarely possible to entirely prevent these
attacks.
The current authors regard the cryptographically generated
addresses (Sec. 3.2 ) and return routability tests (Sec. 3.3 ) as
the most promising solutions for BU authentication. In situations
where public-key cryptography is considered too expensive, the best
solution may be be to assume a safe network route (Sec. 3.4 ).
3.1 Public Key Authentication (o)
An obvious solution to Mobile IPv6 authentication would be to use a
suite of strong generic authentication mechanisms such as IPSec,
IKE, and a PKI. The current lack of a standard BU authentication
protocol can thus be seen as a consequence of the commercial
failure of PKIs and the slow pace of the IPSec standardization
process.
There are, however, other reasons (than unavailability) why the
generic protocol suites may not be good for BU authentication.
First, the generic authentication protocols have usually been
designed with general-purpose computers and application-level
security in mind. The computation and communication overhead of
these protocols may be too high for low-end mobile devices and for
a network-level signaling protocol. Second, the Mobile IPv6
protocol is carefully designed to accommodate any Internet host as
mobile and all hosts as correspondents. This means that a single
PKI should cover the entire Internet, which is clearly a formidable
goal when even local infrastructures have failed to emerge at the
expected rate. Therefore, it is necessary to look for alternative
solutions that do not rely on such global infrastructures.
There are nevertheless situations where it is possible, and
advisable, to apply the generic authentication solutions. In closed
user groups and high-security environments, it may be possible to
set up a PKI and require BUs to be strongly authenticated.
3.2 Cryptographically Generated Addresses
A recently discovered technique provides an intermediate level of
security below strong public-key authentication and above routing-
based weak methods (which will be described in the following
sections). The idea, originally introduced in a BU authentication
protocol called CAM [OR01], is to form the last 64 bits of the IP
address (the interface identifier) by hashing the host's public
signature key. Binding Updates can then be signed with this key. A
secure one-way hash function makes it difficult for the attacker to
come up with a key that matches a given address and to forge signed
BUs. The attraction of this technique is that it provides public-
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key authentication independent of any trusted third parties, PKI,
or other global infrastructure.
The main weakness of the scheme is that only 62-64 bits of the IP
address can be used for the hash. Thus, an attacker may be able to
mount a brute force attack and find a matching signature key by
trial and error. It is relatively expensive to generate strong
signature keys but the attacker does not need to care about the
strength of the keys. There may be relatively fast ways of
generating weak signature keys, which the correspondent may not
able to tell apart from strong ones. In order to make such brute-
force attacks less attractive, one should include the routing
prefix of the network into the hash. This forces the attacker to
perform the search separately for each prefix. Without this, a
global table of all hash values and their corresponding keys might
become feasible in the future, even if that seems out of practical
reach given current storage technology. A mechanism for generating
new public keys and changing addresses at regular intervals should
also discourage brute-force attacks against individual hosts.
Another limitation of the cryptographically generated addresses
(CGA) is that although they prevent the theft of another host's
address, they do not stop the attacker from inventing new false
addresses with an arbitrary routing prefix. The attacker can
generate a public key and a matching IP address in any network and
use it to mount bombing attacks (as described in Sec. 2.5 -2.6 ).
While the public-key protocols (both PKI-based and CGA-based ones)
provide a reasonable protection against unauthentic BUs, they are
computationally intensive and therefore expose the participants to
denial-of-service attacks (see Sec. 4.1 -4.2 ).
3.3 Return Routability for HoA and CoA (*)
One way to limit the number of attackers and their targets is to
test the return routability (RR) of the HoA and CoA. That is, the
correspondent sends packets to both addresses and accepts Binding
Updates only from mobiles that are able to receive them. Some
malicious entities (e.g. ones on the correspondent's local network)
may be able to capture one or both packets but most Internet users
do not have such capabilities. A typical attacker is able to attack
only the correspondents in its own local network. The RR test is,
in fact, a variation of the cookie exchange, which has been used as
part of the TCP handshake [SKK+97] and in authentication protocols,
including Photuris [KS99] and IKE [HC98].
Arguments have been made as to whether the RR test should be done
for HoA, CoA, or both. In the following, we will explain what kind
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of attacks each test prevents and conclude that both tests are
needed.
The RR test for HoA can be seen as a weaker alternative to CGA or
other public-key authentication. In order to subvert the
authentication, the attacker must be on the route between the
correspondent and the HoA. But as we will see below, the
routability test for HoA provides other guarantees in addition to
mobile authentication, which make it is complementary, rather than
alternative, to CGA authentication.
The RR for CoA prevents the bombing of third parties at CoA (Sec.
2.5 ). The attacker has to be able to receive the packet sent to
the CoA, which means that the attacker must have recently visited
the target network. This is a way of checking that the mobile is
not lying about its location. Thus, the test has to be repeated
every time the mobile moves to a new location. This provides a
level of authentication but is not entirely secure because the
attacker could be somewhere on the path from the correspondent to
the CoA.
The bombing attacks against HoA (Sec. 2.6 ) gets around the RR test
for CoA (and other the defense mechanisms that somehow verify the
correctness the CoA). The first logical reaction to this would be
to verify the new location of the mobile no matter if it arrives to
a new CoA or to HoA. Unfortunately, it may be impossible to execute
a RR test for HoA when a Binding Cache entry is cancelled or
expires. The mobile may be unreachable at that time or it may
refuse to co-operate in the authentication protocol.
What makes the situation difficult is that if the RR test for HoA
fails, the correspondent cannot simply drop the cache entry because
that is exactly what the attacker would want. However, we believe
that it is desirable for the correspondent to be able to delete the
Binding Cache entry at any time without executing any further
protocols. Therefore, we suggest that the RR test for HoA should be
performed regularly during the lifetime of a Binding Cache entry.
That way, when the cache entry needs to be deleted for any reason
(e.g. BU cancellation, expiring cache entry, or failing
authentication), a recent RR test for HoA has always been
performed. This prevents bombing of HoA unless the attacker has
recently visited that address (or other on-path location where it
can receive packets from the correspondent to the HoA).
We propose the following guidelines for combining the mechanisms:
- Before creating a Binding Cache entry, do authenticated key
exchange with CGA, RR test for HoA, and RR test for CoA.
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- Before a Binding Cache entry is updated with new CoA, do RR test
for CoA.
- Periodically do RR for HoA. The best time to do this is before
refreshing the Binding Cache entry with unchanged CoA but the
test must not be postponed indefinitely if the mobile changes
its CoA in every BU. (One way to implement this is to limit the
lifetime of Binding Cache entries.)
The RR test for HoA could executed be more frequently, e.g. every
few minutes, in protocols that rely on the RR test for
authentication and less often, e.g. every hour, with CGA
authentication. This is because CGA removes the need for the RR
authentication function and also prevents the bombing of individual
addresses. The benefit from such optimization is, however, limited,
because the cost of the RR test is lowest when the mobile is not
moving and the BU protocol can be executed in the background well
before the Binding Cache entry expires. It might, therefore, be
simplest to do both RR tests every time when the cache entry is
updated without changing CoA.
If the CGA authentication or one of RR tests fails, the
correspondent should ignore the Binding Update and allow the
Binding Cache entry expire.
Interestingly, there is an argument for doing RR for CoA in the
transport layer rather than in the IP layer. The flooding problem
is related to flow control: the correspondent is redirecting a data
flow into a new route and needs to verify that this route can
accept the data. For TCP streams, the natural solution would be to
reset the window size to the initial window size (1 or 2 packets).
This would, in effect, test return routability of the new route
before sending large amounts of data into it. However, mandating
secure RR testing in all transport protocols and changing existing
implementations would not be possible in practice. Therefore, the
best solution is to do the RR tests in the IP layer.
3.4 Assuming a safe route
Some proposed BU authentication protocols make the assumption that
the communication between two specific hosts is safe from
attackers, even though it is not cryptographically protected. For
example, the return routability test for HoA (Sec. 3.3 ) can
replace public-key authentication of the mobile if one is prepared
to assume that the route from the correspondent to the mobile's
Home Agent is secure. (Note that the RR test for HoA has two
separate functions: authentication of the mobile and protection of
the HoA against flooding.)
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The assumption may be reasonable because the average Internet host
cannot listen to or modify packets on the specific routers.
Moreover, even an attacker in control of some routers can only
interfere with communication between a limited number of hosts
because most Internet traffic will not be routed through the
compromised routers.
The assumption can be justified also by the fact that an attacker
on the route between two fixed hosts (a mobile at home and a
correspondent) can mount equally damaging attacks against the
communication between them.
3.5 Two Independent Routes
Some weak BU authentication schemes have been proposed (Bake
[NP01], HA Cookies [TO01]) where the security essentially depends
on sending two pieces of the authentication data between the
correspondent and the mobile or its Home Agent through two
independent routes and hoping that most attackers are unable to
capture both of them. This may not help as much as has perhaps been
hoped. In all these protocols, a single attacker on the route
between the correspondent and Home Agent can spoof BUs by
pretending to be both the mobile and its Home Agent. If the
attacker uses its own address as the false CoA, it can spoof
packets from both the mobile and the Home Agent to the
correspondent, and it can receive messages sent by the
correspondent to both HoA and CoA. This means that the protocols
essentially make the same assumption about a single safe route as
we proposed in the previous section.
Without ingress filtering at the attacker's local network, the
attacker is, in fact, able to select an arbitrary CoA. Ingress
filtering at the attacker's network forces the attacker to use a
CoA from its local network. (The Alternate CoA sub-option could be
used to get around this.) Ingress filtering also prevents attacks
against the HA Cookie protocol because the attacker could not spoof
packets from Home Agent to the correspondent.
A false sense of security is created if one assumes that the three
sides of the triangle in MIPv6 triangle routing are independent
routes. This is usually the case for an authentic mobile, but need
not be true not for an attacker who claims to be the mobile. When
the false mobile (i.e. the attacker) is on the route between the
correspondent and the Home Agent, the triangle collapses. (When
thinking about the protocols one easily starts arguing in terms of
active and passive attackers. It is worth remembering here that all
attacks against BU protocols are essentially active, as we
explained at the beginning of Sec. 2.)
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On the other hand, if one finds it reasonable to assume a safe
route, i.e. that the attacker cannot listen to traffic between the
correspondent and the Home Agent, then an equivalent level of
security is achieved by a much simpler protocol: the correspondent
sends a secret key in plaintext to HoA and Home Agent forwards it
through a secure tunnel to the mobile. (This is a variation of the
RR test for HoA.) We believe that however ridiculous this may
sound, it may sometimes be the best solution for BU authentication.
3.6 Leap of Faith
Yet another idea that has been floating around is that if the
mobile sends a session key insecurely to the correspondent at the
beginning of a connection, the key can be used to authenticate
subsequent BUs (so called leap-of-faith authentication). This is a
flawed proposition. It fails even if we assume that attacker is
unlikely to capture the keys sent by authentic mobiles. First, the
attacker can send its false key before the authentic mobile sends
the authentic key. Second, there must be a recovery mechanism for
situations where the mobile or the correspondent loses its state,
and the attacker can exploit this mechanism.
The leap-of-faith authentication is suitable for situations where a
human user, or some other factor outside the attacker's control, at
random times initiates the protocol. The party making the leap must
always be the one that initiates the protocol. In such situations,
it may be reasonable to argue that an attacker is unlikely to be
present at the time of the unauthenticated key exchange. In BU
authentication, the protocol is usually initiated by the mobile but
the leap in faith should be made by the correspondent. Also, the
attacker can trigger the BU protocol at any time by sending a
spoofed packet from the correspondent to the mobile's HoA.
3.7 The Role of Ingress Filtering (o)
Ingress filtering is another way of limiting the number of
potential attackers and their targets. As we have noted above, many
of the attacks against Route Optimization involve spoofed source IP
addresses and are, thus, prevented by ingress filtering. There are
two well-known weaknesses in this thinking, though. Firsts, ingress
filtering must be applied on the attacker's local network; on the
target network it makes no difference. Second, the Home Address
Option and the Alternate Care-of Address sub-option can be used for
similar source spoofing. While it is advisable to apply ingress
filtering in as many networks as possible, one cannot rely on this
to stop all attackers.
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4. DoS Attacks against BU Authentication
Security protocols that successfully protect the secrecy and
integrity of data can sometimes make the participants more
vulnerable to denial-of-service attacks. In fact, the stronger the
authentication, the easier it may be for an attacker to use the
protocol features to exhaust the mobile's or the correspondent's
resources.
4.1 Inducing Unnecessary Binding Updates
When a mobile host receives an IP packet from a new correspondent
via the HoA, it automatically sends a Binding Update to that
correspondent. The attacker can exploit this by sending the mobile
spoofed IP packets (e.g. ping or TCP SYN packets) that appear to
come from different correspondent addresses. The attacker will
automatically start the BU protocol with these correspondents. If
the correspondent addresses are real addresses of existing IP
hosts, then most instances of the BU protocol will complete
successfully. The entries created in the Binding Cache are correct
but useless. This way, the attacker can with little work induce the
mobile to execute the BU protocol unnecessarily, which can drain
the mobile's resources.
A correspondent (i.e. any IP host) can also be attacked in a
similar way. The attacker sends spoofed IP packets to a large
number of mobiles with the target host's address as the source
address. These mobiles will all send Binding Updates to the target
host. Again, most of the BU protocol executions will complete
successfully. By inducing a large number of unnecessary BUs, the
attacker is able to consume the target host's resources.
This attack is possible against any BU authentication protocol. The
more resources the Binding Update protocol consumes, the more
serious the attack. Hence, strong cryptographic authentication
protocol is more vulnerable to the attack than a weak one or
unauthenticated BUs.
A host should protect itself from the attack by setting a limit on
the amount of resources, i.e. processing time, memory, and
communications bandwidth, which it uses for processing BUs. When
the limit is exceeded, the host can simply stop Route Optimization.
(See Sec. 5.2 .) Sometimes it is possible to process some BUs even
when a host is under the attack. A mobile host may have a local
security policy listing a limited number of addresses to which BUs
will be sent even when the mobile host is under DoS attack. A
correspondent (i.e. any IP host) may similarly have a local
security policy listing a limited set of addresses from which BUs
will be accepted even when the correspondent is under a DoS attack.
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The host may also recognize addresses with which they have had
meaningful communication in the past and sent BUs to or accept them
from those addresses.
Ingress filtering at the attacker's local network mitigates the
attacks. When flooding a mobile, the attacker can only choose
correspondent addresses in its own local network. When flooding a
correspondent, the attacker can only target correspondents in its
own network. Unfortunately, the Home Address Option (HAO) can be
used to circumvent the ingress filtering and to spoof packets from
any correspondent. It has been questioned whether the HAO should be
allowed in all packets, or only on those that are associated with
an already successfully created Binding Cache Entry. The latter
would prevent the use of HAOs in DoS attacks against BU
authentication.
In the following section, we will explain some additional DoS
attacks and defense mechanisms. However, these attacks are
generally no more serious than the ones described in this section.
It usually does not pay to defend against the other types of
attacks unless one can also prevent the attacks of this section.
4.2 Consuming Authentication Resources
Authentication protocols are often vulnerable to flooding attacks
that exploit the protocol features to consume the target host's
resources. Computing power is consumed by flooding the host with
messages that cause it to perform expensive cryptographic
operations. If a host creates state during protocol execution, it
is also vulnerable to attacks where the attacker starts excessive
numbers of protocol runs and never finishes them.
In order to exhaust the computing power of modern processors, the
attacker needs to get them to perform public-key cryptographic
operations. To do this, they may, for example, spoof large numbers
of signed messages where the signatures are replaced by random
numbers. The target host must verify the signatures before
rejecting the messages. Symmetric encryption, cryptographic hash
functions, and non-cryptographic computation are rarely the
performance bottleneck. However, if the cryptographic library is
optimized only for bulk data, it may behave inefficiently when the
functions are invoked on millions of short messages and the keys
are changed on every invocation.
One way protocols can avoid the unnecessary public-key operations
is to require a weak authentication, such as a cookie exchange,
before doing the expensive computation. Attacks against stateful
protocols can be prevented by making the protocol parties stateless
until the honesty of the other participant has been proved or by
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designing the stare management with flooding attacks in mind. (See
Sec. 5.1 .)
4.3 Forcing Non-Optimized Routing (o)
If the BUs are not authenticated, the attacker can prevent a
correspondent from using Route Optimization by filling its Binding
Cache with false entries so that most entries for real mobiles are
dropped. With authenticated BUs, the attacker can mount the same
attack by inducing unnecessary Binding Updates that create
authentic but unnecessary cache entries (see Sec. 4.1 ).
Any successful DoS attack against a mobile or a correspondent can
also prevent the processing of BUs. We have repeatedly suggested
that the target of a DoS attack may respond by stopping Route
Optimization for all or some communication. Obviously, an attacker
can exploit this fallback mechanism and force the target to use the
less efficient triangle routing. The attacker only needs to mount a
noticeable DoS attack against the mobile or correspondent, and the
target will default to non-optimized routing.
The target host can mitigate the effects of the attack by reserving
more space for the Binding Cache, by reverting to non-optimized
routing only when it cannot otherwise cope with the DoS attack, by
trying aggressively to return to optimized routing, and by favoring
mobiles with which it has an established relationship. This attack
is not as serious as the ones described earlier, but applications
that rely on Route Optimization could still be affected. For
instance, conversational multimedia sessions can suffer drastically
from the additional delays caused by triangle routing.
4.4 Reflection and Amplification (*)
Attackers sometimes try to hide the source of a packet flooding
attack by reflecting the traffic from other hosts [Sav02]. That is,
instead of sending the flood of packets directly to the target, the
attacker sends data to other hosts, tricking them to send the same
number, or more, packets to the target. Such reflection can hide
the attacker's address even when ingress filtering prevents source
address spoofing. Reflection is particularly dangerous if the
packets can be reflected multiple times, if they can be sent into a
looping path, or if the hosts can be tricked into sending many more
packets than they receive from the attacker, because such features
can be used to amplify the traffic by a significant factor. When
designing protocols, one should avoid creating services that can be
used for reflection and amplification.
Triangle routing easily creates opportunities for reflection:
Correspondent receives packets (e.g. TCP SYN) from the mobile and
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replies to the home address given by the mobile (in a HAO). The
mobile might not really be a mobile and the HoA could actually be
the target address. The target at the HoA only sees the packets
sent by the correspondent and cannot see the attacker's address
(even if ingress filtering prevents the attacker from spoofing its
source address).
The BU protocol could also be used for reflection: the
correspondent responds to a data packet or to an unauthenticated BU
by initiating the BU authentication protocol, which usually
involves sending a packet to HoA. In that case, the reflection
attack can be discouraged by copying the mobile's address into the
messages sent by the mobile to the correspondent. (The mobile's
source address is usually the same as the CoA but an Alternative
CoA suboption can specify a different CoA.)
In some proposed BU authentication protocols (e.g. one we co-
authored [Roe02]), the correspondent responds to an initial message
from the mobile with two packets (one to HoA, one to CoA). This can
be used to amplify a flooding attack by a factor of two.
Furthermore, with public-key authentication, the packets sent by
the correspondent may be significantly larger than the one that
triggers them.
These types of reflection and amplification could be avoided by
ensuring that the correspondent only responds to the same address
from which it received a packet, and only with a single packet of
the same size. Depending on the BU protocol, this might require an
increased number of messages and a reverse tunneling mechanism for
sending packets from the mobile through the Home Agent to the
correspondent. The question that needs to be decided is whether the
cost of these protections is more acceptable than threat created by
a small constant factor of amplification. Padding could be used to
equalize the packet sizes although we believe this would be
unnecessary in practice. The mobile nodes usually have low-
bandwidth access links, which makes them vulnerable to flooding
attack, but high-value targets, such as public servers, rarely are
mobile.
5. Preventing Resource Exhaustion
In this section, we describe defenses against denial-of-service
attacks that exploit features of the BU protocol to exhaust the
target host's resources. As it usually is impossible to completely
prevent DoS attacks, the right approach is to increase the cost and
difficulty of the attacks and to mitigate their effects.
5.1 Delaying Commitment
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A standard protection against DoS attacks is to delay committing
one's resources to the protocol until the other party has provided
some assurance about its honesty. This assurance could, for
example, be authentication or expensive computation of resources by
the other party.
Expensive public-key operations can be delayed by starting with a
weak but inexpensive authentication mechanism and by proceeding
with the public-key operations only after the weak authentication
succeeds [Mea99]. This either limits the number of attackers who
can get to the public-key stage or increases the cost of the attack
by forcing the attacker to break the weak mechanism. For example, a
BU authentication protocol could start with a cookie exchange or,
preferably, with a RR test for both HoA and CoA (see Sec. 3.3 ),
and continue with a public-key authentication only if the RR test
succeeds.
Memory space for storing protocol state is another resource that
attackers can exhaust. The conventional way to defeat attacks that
consume state storage is to reserve enough memory for storing the
state data and to manage the storage efficiently. Another method is
to remain stateless until the authentication is complete [AN97a].
Hosts with little memory and implementations aiming for simplicity
are particularly likely to find the stateless approach easier. We
therefore recommend the that BU authentication protocol should
allow stateless implementation of the correspondent. On the other
hand, there is no compelling reason to require statelessness for
hosts that can manage the state data in other ways.
There are some difficulties in making the BU authentication
protocol stateless, which should be understood. The main difficulty
is that usually only the responder can be stateless, and it is not
clear which party initiates the Binding Update process and which
one responds. While the mobile normally initiates the
authentication, this may be triggered by a packet belonging to
another protocol that arrived from the correspondent. Moreover, if
a packet from the correspondent triggers the BU, the correspondent
may not know that this was the case. A further complication is that
once an upper layer protocol has created a protocol state, it is of
little value to refrain from doing so in the lower layers, but the
IP layer cannot know when this is happening. For simplicity, we
recommend making the correspondent stateless and advice against
trying to guess which party initiated the protocol and whether the
statelessness is necessary or not. We choose protection of the
correspondent over the mobile for two reasons. First, any Internet
host can be a correspondent. Second, it is less practical to make
the mobile stateless because the mobile usually does not
authenticate the correspondent and, thus, there is no clear point
after which it is safe to create a state. We acknowledge that the
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mobile is likely to have more stringent memory constraints than the
correspondent and it may be left vulnerable to the state storage
exhaustion attacks.
Cryptographic puzzles [JB99][ANL00] are another proposed protection
against resource-exhaustion attacks. A server requires its clients
to solve a cryptographic puzzle (e.g. brute-force search for some
input bits of a one-way function) before committing its own
resources to the protocol. The server can adjust the difficulty of
the puzzles according to its load. Solving the puzzle creates a
small cost for each protocol invocation, which makes flooding
attacks expensive but has little effect on honest hosts.
Unfortunately, there are several drawbacks to this strategy in the
Mobile IPv6 protocol. First, the IP layer does not know which one
of the nodes, the mobile or the correspondent, is the server (i.e.
the respondent). Second, mobile nodes can have extremely limited
processor and battery capacity, which makes the cost of solving
puzzles too high for them, while an attacker pretending to be a
mobile is likely have much more computational capacity. The puzzle
protocols work well only when all clients have approximately equal
computational capacity.
5.2 Controlling Damage
As we suggested in Sec. 4.1 , a host can protect itself from
flooding attacks by limiting the amount of resources it uses for BU
authentication. It can set limits on the processor time, memory and
communications capacity used for this purpose. When this limit is
exceeded, the host should stop all further participation in BU
authentication protocols. It may stop processing BUs and let all
Binding Cache entries expire. Alternatively, it may continue to
update entries already in the Binding Cache if there is a light-
weight mechanism (e.g. a session key) for re-authenticating them.
The effect of this is to stop Route Optimization for all
communication, or only for new connections. The host may return to
normal operation when it believes the attack is over.
Since authentication cannot prevent all the attacks, every host
SHOULD implement the limit on resource usage. A host that does not
implement the limit will be vulnerable to flooding attacks but it
will not cause any damage to other hosts.
5.3 Favoring Regular Customers
A correspondent can give priority to mobiles with which it has a
long-term relationship or recent meaningful communication in the
upper protocols layers. The mobile may similarly favor selected
correspondent addresses. The best way to secure Binding Updates
when the hosts have a long-term relationship is to use an
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authenticated IPSec tunnel. The following techniques should only be
used when it is not possible to configure an IPSec Security
Association.
A host's local policy may have a list of addresses or address
ranges, to and from which BUs are processed even when the host is
under stress from attacks. These should not include addresses for
which it is feasible to establish long-term IPSec Security
Associations. The list of addresses should not be large or public
because otherwise the attacker might be able to mount the attack by
using only these addresses. Taking into account authentication and
other displays of commitment in the upper protocol layers can be
difficult to implement because it violates the stateless nature of
the IP protocol layer and creates dependences between protocol
layers. In some common situations, it may be worth while to violate
the layering principle. For example, a Web server could accept BUs
from its clients after it has successfully executed the TCP
handshake.
It may also help to keep updating the existing entries in the
Binding Cache so that existing optimized routes can be maintained
during the attack, although it is not certain that the existing
cache entries belong to the most important mobiles or even to
authentic ones. Some indication of this may be inferred from the
packet counts associated with the traffic flowing through the
entry.
6. The Right Level of Protection
We will conclude this document by discussing the criteria that
should be used for selecting and comparing BU authentication
protocols and issues that arise when there are several alternative
protocols.
6.1 Prioritizing the Goals (*)
The strength of the protection against DoS attacks that do not
corrupt routing tables is independent of the strength of the BU
authentication. As we have observed, strong authentication
mechanisms may even enable DoS attacks that would not otherwise be
possible. Nevertheless, the following principles apply to all
attacks.
- A protection mechanism MUST be implemented and used if security
of other hosts or communication between other hosts depends on
it (except in cases covered by the next bullet).
- A protection mechanism SHOULD be implemented if communication
between the host itself and others depends on it.
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- A protection mechanism SHOULD be implemented if only the host's
own security depends on it.
- Some hosts, e.g. minimal implementations, MAY elect not to
protect themselves and their own connections against all the
attacks as long as that does not compromise the protection for
others.
Since Route Optimization is an optimization, a host MAY always
protect itself and others by ignoring all Binding Updates, which
means giving up Route Optimization. A slightly smarter host MAY
implement only the mandatory mechanisms that help protect others
and stop using Route Optimization when it detects a DoS attack
against itself.
The most serious attack is the bombing of third parties with
unwanted data (Sec. 2.5 -2.6 ) because they cannot do anything to
stop the flood of data. All mobiles and correspondents MUST either
implement and use some kind of protection against this attack, or
ignore all Binding Updates and give up Route Optimization.
Attacks against correspondent hosts that accept Binding Updates
form the second most serious class of attacks. This includes
attacks on data secrecy and integrity as well as denial-of-service
attacks. Every IP host is a potential correspondent and if the
Mobile IP protocol makes them vulnerable, then every IP host is
vulnerable. It is important that reliable protection mechanisms are
available for the correspondents and every IP host SHOULD implement
and use these mechanisms to protect itself. If the protection for
the correspondents requires support from mobiles, all mobile hosts
MUST implement and use the supporting functionality.
Finally, there are the attacks against the mobiles. As with
correspondents, it is important to have protection mechanisms for
the mobiles and they SHOULD be implemented and used. Any necessary
supporting functionality in the correspondents MUST be implemented
and used. Although attacks against mobile hosts cannot bring down
the Internet as we know it, the number and significance of mobiles
will increase. If Mobile IPv6 is to become the primary mobility
protocol in the Internet, it is essential to protect its
reliability against malicious parties.
6.2 Multiple Levels of Authentication (*)
The computational and communications capabilities of Internet hosts
vary vastly, as does the level of security they require. It would,
therefore, be desirable to have a range of BU authentication
protocols with different cost and security trade-offs. For example,
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closed high-security groups could use pre-established shared keys
or a PKI, most hosts CCA authentication with return routability
tests for DoS prevention, and low-end mobile devices a protocol
based only on RR. However, care must be taken to accommodate the
multiple levels of protection so that the attacker cannot bid down
to the lowest level.
In the end, the decision about accepting or not accepting a BU is
made by the correspondent. Therefore, the correspondent will always
make the final decision about the required level of authentication
(e.g. CGA/RR or plain RR) for the particular HoA. Also, it makes
little sense for the correspondent to allow multiple levels of
authentication for the same HoA because the attacker could always
tackle the weakest one. Thus, the mobile must either authenticate
itself using the protocol chosen by the correspondent or give up
Route Optimization. It makes little sense to negotiate the
protocol.
In order to conform to the principles of the previous section, any
protocol chosen by the correspondent must provide whatever level of
DoS protection is considered sufficient for the mobile and for
third parties. Thus, the protocols will mostly differ in DoS
protection for the correspondent itself, which the correspondent
may freely tune, and in the strength of the authentication. It is
worth noting that different correspondents can make their choices
of authentication strength independently. This is because a weak
mechanism accepted by one correspondent would not help the attacker
to redirect packets to or from correspondents that use a stronger
protocol.
It is advisable that the default protocol, used for mobiles with
which the correspondent has not prior relationship, be the
strongest one which correspondent can afford under normal use.
Typically, this could be CGA/RR. This default level of
authentication MUST be statically configured at the correspondent
and MUST NOT be adjusted according to the current load. Otherwise,
the attacker could artificially induce the conditions under which a
weaker protocol is chosen.
The correspondent MAY have a local policy that mandates a higher
level (e.g. shared key authentication or PKI) or lower level (e.g.
plain RR) of authentication for a particular HoA or range of
addresses. These addresses can be statically configured or
dynamically determined by strong authentication or equivalent
commitment shown by the mobile in upper protocol layers. For
example, a correspondent could be configured to allow weaker
authentication for some low-end mobile devices that benefit from
Route Optimization but cannot afford to run the stronger
authentication protocol.
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It would be possible to allocate one bit of the IP address, similar
to the "u" and "g" bits [HD98] in the interface identifier, to
indicate whether the address is a CGA address. The correspondent
would then select the BU protocol based on this bit. A disadvantage
of this scheme is that the length of the public-key hash would
become one bit shorter. Also, there may be increasing pressure to
allocate bits of the IPv6 address for various purposes and the 64-
bit interface identifier may soon prove to be surprisingly short.
The problem can be mitigated by requiring only mobile hosts (rather
than all IP nodes) to set the CGA-bit correctly.
Based on the above, it should be recommended (or possibly even
mandated) that the mobiles implement all common BU protocols (e.g.
both CGA/RR and plain RR). If one does not, it may be unable to use
Route Optimization with many correspondents. There is also the risk
that business reasons will force practically all IP nodes to use
the weakest level of authentication that is mandatory to implement
and use. For example, if many low-end mobiles only implement the
weakest standardized protocol, virtually all correspondents will
default to this mechanism, which would defeat the purpose of having
any stronger protocol.
7. Security Considerations
This document discusses security of Mobile IPv6 Route Optimization
but does not present any specific protocols or detailed solutions.
A separate specification of the actual BU authentication protocol
is needed.
There are other security concerns with Mobile IPv6 that are not
addresses in this document. The Home Agent Discovery needs to be
secured so that the mobile can establish a secure tunnel to a
reliable Home Agent. Also, some features of the Mobile IPv6
protocol may reduce the effectiveness of ingress filtering. The
Home Address Option, the Alternative CoA sub-option, and possibly
IPv6 in IPv6 tunnels, may be used to spoof the origin of packets
without spoofing the source IP address.
We assume that the mobile has chosen a reliable Home Agent and that
Binding Updates and Acknowledgments between the mobile and its Home
Agent are strongly authenticated with techniques outside the scope
of this document. For example, there could be a manually keyed
IPSec tunnel to a router on the mobile's Home Network. There are
situations where no secure tunnel exist, for example if the mobile
automatically contracts the services of temporary Home Agents along
its path, but we feel that the security in such situations is based
on much weaker assumptions and should be considered separately.
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It seems necessary to send the Binding Acknowledgments from other
sources than the Home agent without authentication. In most BU
authentication protocols, only the mobile is authenticated, and
without authenticating the correspondent, there is no way of
authenticating the acknowledgments. The consequence is that an
attacker can send false acknowledgments and cause the mobile to
send the next BU sooner or later than the correspondent expects. At
worst, the effect is that the Binding Cache entry expires and Route
Optimization is not used. Thus, an attacker anywhere on the network
can prevent the use of Route Optimization by sending false Binding
Acknowledgments.
Finally, where an authenticated IPSec tunnel between the mobile and
the correspondent exists, Binding Updates can be sent through the
tunnel. However, the return routability test for DoS prevention
might still be needed. We feel that currently the simplest and most
effective solution is to design the BU protocol independently of
IPSec.
8. Conclusions
We have described attacks against Mobile IPv6 Route Optimization
and mechanisms for protecting the protocol participants and third
parties. Some of the attacks may be new in the sense that they have
not been considered in earlier BU authentication requirements and
protocol drafts. It is our hope that this document will help in
designing BU authentication protocols and in the process of
choosing the protocol or protocols that will be part of the Mobile
IPv6 standard. We are also working on a family of protocols that
takes into account the points of this document [Roe02].
Acknowledgments
Many of the ideas originate from Mike Roe, Greg O'Shea, Pekka
Nikander, Erik Nordmark and various Internet Drafts.
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progress.
[Roe02] Michael Roe, Tuomas Aura, Greg O'Shea, and Jari Arkko.
Authentication of Mobile IPv6 binding updates and
acknowledgments. Internet Draft draft-roe-mobileip-
updateauth-02.txt, IETF Mobile IP Working Group, February
2002. Work in progress.
[Sav02] Pekka Savola. Security of IPv6 routing header and home
address options. Technical report, IETF, November 2002.
Work in progress.
[SKK+97] Christoph L. Schuba, Ivan V. Krsul, Markus G. Kuhn,
Eugene H. Spaffold, Aurobindo Sundaram, and Diego
Zamboni. Analysis of a denial of service attack on TCP.
In Proc. 1997 IEEE Symposium on Security and Privacy,
pages 208-223, Oakland, CA USA, May 1997. IEEE Computer
Society Press.
[TO01] Michael Thomas and Dave Oran. Home agent cookies for
binding updates. Internet Draft draft-thomas-mobileip-ha-
cookies-00.txt, IETF, July 2001. Work in progress.
Authors' Addresses
Tuomas Aura
7 J J Thompson Avenue
Cambridge, CB3 0FB
United Kingdom
Phone: +44 1223 479708
Email: tuomaura@microsoft.com
Jari Arkko
Oy LM Ericsson Ab
02420 Jorvas
Finland
Phone: +358 40 5079256
Email: Jari.Arkko@ericsson.com
Aura, Arkko Expires August 28, 2002 [Page 27]