draft-ietf-manet-smf-sec-threats-02.txt   draft-ietf-manet-smf-sec-threats-03.txt 
Mobile Ad hoc Networking (MANET) J. Yi Mobile Ad hoc Networking (MANET) J. Yi
Internet-Draft T. Clausen Internet-Draft T. Clausen
Intended status: Informational LIX, Ecole Polytechnique Intended status: Informational LIX, Ecole Polytechnique
Expires: September 24, 2015 U. Herberg Expires: May 9, 2016 U. Herberg
Fujitsu Laboratories of America November 6, 2015
March 23, 2015
Security Threats for Simplified Multicast Forwarding (SMF) Security Threats for Simplified Multicast Forwarding (SMF)
draft-ietf-manet-smf-sec-threats-02 draft-ietf-manet-smf-sec-threats-03
Abstract Abstract
This document analyzes security threats of the Simplified Multicast This document analyzes security threats of the Simplified Multicast
Forwarding (SMF), including the vulnerabilities of duplicate packet Forwarding (SMF), including the vulnerabilities of duplicate packet
detection and relay set selection mechanisms. This document is not detection and relay set selection mechanisms. This document is not
intended to propose solutions to the threats described. intended to propose solutions to the threats described.
Status of this Memo Status of this Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 24, 2015. This Internet-Draft will expire on May 9, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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potentially exposed to different kinds of attacks and potentially exposed to different kinds of attacks and
misconfigurations. Some of the threats are of particular misconfigurations. Some of the threats are of particular
significance as compared to wired networks. In [RFC6621], SMF does significance as compared to wired networks. In [RFC6621], SMF does
not define any explicit security measures for protecting the not define any explicit security measures for protecting the
integrity of the protocol. integrity of the protocol.
This document is based on the assumption that no additional security This document is based on the assumption that no additional security
mechanism such as IPsec is used in the IP layer, as not all MANET mechanism such as IPsec is used in the IP layer, as not all MANET
deployments may be suitable to deploy common IP protection mechanisms deployments may be suitable to deploy common IP protection mechanisms
(e.g., because of limited resources of MANET routers to support the (e.g., because of limited resources of MANET routers to support the
IPsec stack). The document analyzes possible attacks on and mis- IPsec stack). It assumes that there is no lower-layer protection
either. The document analyzes possible attacks on and mis-
configurations of SMF and outlines the consequences of such attacks/ configurations of SMF and outlines the consequences of such attacks/
mis-configurations to the state maintained by SMF in each router. mis-configurations to the state maintained by SMF in each router.
This document aims at analyzing and describing the potential This document aims at analyzing and describing the potential
vulnerabilities of and attack vectors for SMF. While completeness in vulnerabilities of and attack vectors for SMF. While completeness in
such an analysis always is a goal, no claims of being complete are such analysis is always a goal, no claims of being complete are made.
made. The goal of this document is to be helpful for when deploying The goal of this document is to be helpful for when deploying SMF in
SMF in a network and needing to understand the risks thereby incurred a network and needing to understand the risks thereby incurred - as
- as wll as for providing a reference and documented experience with well as for providing a reference and documented experience with SMF
SMF as input for possibly future developments of SMF. as input for possibly future developments of SMF.
This document is not intended to propose solutions to the threats This document is not intended to propose solutions to the threats
described. [RFC7182] provides a framework, which can be used with described. [RFC7182] provides a framework that can be used with SMF,
SMF, and which - depending on how it is used - may offer some degree and depending on how it is used - may offer some degree of protection
of protection against the threats described in this document related against the threats described in this document related to identity
to identity spoofing. spoofing.
2. Terminology 2. Terminology
This document uses the terminology and notation defined in [RFC5444], This document uses the terminology and notation defined in [RFC5444],
[RFC6130] [RFC6621] and [RFC4949]. [RFC6130], [RFC6621] and [RFC4949].
Additionally, this document introduces the following terminology: Additionally, this document introduces the following terminology:
SMF router: A MANET router, running SMF as specified in [RFC6621]. SMF router: A MANET router, running SMF as specified in [RFC6621].
Attacker: A device that is present in the network and intentionally Attacker: A device that is present in the network and intentionally
seeks to compromise the information bases in SMF routers. seeks to compromise the information bases in SMF routers.
Compromised SMF router: An attacker, which generates syntactically Compromised SMF router: An attacker that generates syntactically
correct SMF control messages. Control messages emitted by a correct SMF control messages. Control messages emitted by a
compromised SMF router may contain additional information, or omit compromised SMF router may contain additional information, or omit
information, as compared to a control message generated by a non- information, as compared to a control message generated by a non-
compromised SMF router located in the same topological position in compromised SMF router located in the same topological position in
the network. the network.
Legitimate SMF router: An SMF router, which is not a compromised SMF Legitimate SMF router: An SMF router that is not a compromised SMF
Router. Router.
3. SMF Threats Overview 3. SMF Threats Overview
SMF requires an external dynamic neighborhood discovery mechanism in SMF requires an external dynamic neighborhood discovery mechanism in
order to maintain suitable topological information describing its order to maintain suitable topological information describing its
immediate neighborhood, and thereby allowing it to select reduced immediate neighborhood, and thereby allowing it to select reduced
relay sets for forwarding multicast data traffic. Such an external relay sets for forwarding multicast data traffic. Such an external
dynamic neighborhood discovery mechanism may be provided by lower- dynamic neighborhood discovery mechanism may be provided by lower-
layer interface information, by a concurrently operating MANET layer interface information, by a concurrently operating MANET
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packets and eliminate their redundant forwarding. An Attacker has packets and eliminate their redundant forwarding. An Attacker has
several ways in which to harm the DPD mechanisms: several ways in which to harm the DPD mechanisms:
o It can "deactivate" DPD, so as to make it such that duplicate o It can "deactivate" DPD, so as to make it such that duplicate
packets are not correctly detected, and that as a consequence they packets are not correctly detected, and that as a consequence they
are (redundantly) transmitted, increasing the load on the network, are (redundantly) transmitted, increasing the load on the network,
draining the batteries of the routers involved, etc. draining the batteries of the routers involved, etc.
o It can "pre-activate" DPD, so as to make DPD detect a later o It can "pre-activate" DPD, so as to make DPD detect a later
arriving (valid) packet as being a duplicate, which therefore arriving (valid) packet as being a duplicate, which therefore
won't be forwarded" won't be forwarded. "
The attacks on DPD are detailed in Section 4. The attacks on DPD are detailed in Section 4.
RSS produces a reduced relay set for forwarding multicast data RSS produces a reduced relay set for forwarding multicast data
packets across the MANET. SMF supports the use of several relay set packets across the MANET. SMF supports the use of several relay set
algorithms, including E-CDS (Essential Connected Dominating Set) algorithms, including E-CDS (Essential Connected Dominating Set)
[RFC5614], S-MPR (Source-based Multi-point Relay, as known from [RFC5614], S-MPR (Source-based Multi-point Relay, as known from
[RFC3626] and [RFC7181]), or MPR-CDS [MPR-CDS]. An Attacker can [RFC3626] and [RFC7181]), or MPR-CDS [MPR-CDS]. An Attacker can
disrupt the RSS algorithm, by degrading it to classical flooding, or disrupt the RSS algorithm by degrading it to classical flooding, or
by "masking" certain parts of the routers from the multicasting by "masking" certain parts of the routers from the multicasting
domain. The attacks to RSS algorithms are illustrated in Section 5. domain. The attacks to RSS algorithms are illustrated in Section 5.
4. Threats to Duplicate Packet Detection 4. Threats to Duplicate Packet Detection
Duplicate Packet Detection (DPD) is required for packet dissemination Duplicate Packet Detection (DPD) is required for packet dissemination
in MANET because the packets may be transmitted via the same physical in MANETs because the packets may be transmitted via the same
interface as the one over which they were received. A router may physical interface as the one over which they were received. A
also receive multiple copies of the same packets from different router may also receive multiple copies of the same packet from
neighbors. DPD is thus used to check if an incoming packet has been different neighbors. DPD is thus used to check if an incoming packet
received or not. has been previously received or not.
DPD is achieved by a router maintaining a record of recently DPD is achieved by maintaining a record of recently processed
processed multicast packets, and comparing later received multicast multicast packets, and comparing later received multicast packets
herewith. A duplicate packet detected is silently dropped, and is herewith. A duplicate packet detected is silently dropped and is not
not inserted into the forwarding path of that router, nor is it inserted into the forwarding path of that router, nor is it delivered
delivered to an application. DPD, as proposed by SMF, supports both to an application. DPD, as proposed by SMF, supports both IPv4 and
IPv4 and IPv6 and for each suggests two duplicate packet detection IPv6 and for each suggests two duplicate packet detection mechanisms:
mechanisms: 1) header content identification-based DPD (I-DPD), using 1) header content identification-based DPD (I-DPD), using packet
packet headers, in combination with flow state, to estimate temporal headers, in combination with flow state, to estimate temporal
uniqueness of a packet, and 2) hash-based DPD (H-DPD), employing uniqueness of a packet, and 2) hash-based DPD (H-DPD), employing
hashing of selected header fields and payload for the same effect. hashing of selected header fields and payload for the same effect.
In the following of this section, common threats to packet detection In the following of this section, common threats to packet detection
mechanisms are first discussed. Then the threats to I-DPD and H-DPD mechanisms are first discussed. Then the threats to I-DPD and H-DPD
are introduced separately. The threats described in this section are are introduced separately. The threats described in this section are
applicable to general SMF implementations, no matter if NHDP is used applicable to general SMF implementations, no matter if NHDP is used
or not. or not.
4.1. Common Threats to Duplicate Packet Detection Mechanisms 4.1. Common Threats to Duplicate Packet Detection Mechanisms
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router thus can instruct its neighbors to block forwarding of valid router thus can instruct its neighbors to block forwarding of valid
multicast packets. multicast packets.
For example, in Figure 1, router A forwards a multicast packet with a For example, in Figure 1, router A forwards a multicast packet with a
TTL of 64 to the network. A, B, and C are legitimate SMF routers, TTL of 64 to the network. A, B, and C are legitimate SMF routers,
and X is the compromised SMF router. In a wireless environment, and X is the compromised SMF router. In a wireless environment,
jitter is commonly used to avoid systematic collisions in MAC jitter is commonly used to avoid systematic collisions in MAC
protocols [RFC5148]. An attacker can thus increase the probability protocols [RFC5148]. An attacker can thus increase the probability
that its invalid packets arrive first by retransmitting them without that its invalid packets arrive first by retransmitting them without
jittering. In this example, router X forwards the packet without jittering. In this example, router X forwards the packet without
jittering, and reduces the TTL to 1. Router C thus records the jittering and reduces the TTL to 1. Router C thus records the
duplicate detection value (hash value for H-DPD, or the header duplicate detection value (hash value for H-DPD, or the header
content of the packets for I-DPD) but stops forwarding it to the next content of the packets for I-DPD) but stops forwarding it to the next
hops because of the TTL value. When the same packet with normal TTL hops because of the TTL value. When the same packet with normal TTL
value (63 in this case) arrives from router B, it will be discarded value (63 in this case) arrives from router B, it will be discarded
as duplicate packet. as duplicate packet.
.---. .---.
| X | | X |
--'---' __ --'---' __
packet with TTL=64 / \ packet with TTL=1 packet with TTL=64 / \ packet with TTL=1
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network (a directional antenna, a tunnel to a collaborator or a wired network (a directional antenna, a tunnel to a collaborator or a wired
connection, allowing it to bridge parts of a network otherwise connection, allowing it to bridge parts of a network otherwise
distant), it can make sure that the packets with such an artificially distant), it can make sure that the packets with such an artificially
reduced TTL arrive before their unmodified counterparts. reduced TTL arrive before their unmodified counterparts.
4.2. Threats to Identification-based Duplicate Packet Detection 4.2. Threats to Identification-based Duplicate Packet Detection
I-DPD uses a specific DPD identifier in the packet header to identify I-DPD uses a specific DPD identifier in the packet header to identify
a packet. By default, such packet identification is not provided by a packet. By default, such packet identification is not provided by
the IP packet header (for both IPv4 and IPv6). Therefore, additional the IP packet header (for both IPv4 and IPv6). Therefore, additional
identification header, such as the fragment header, a hop-by-hop identification headers, such as the fragment header, a hop-by-hop
header option, or IPSec sequencing, must be employed in order to header option, or IPSec sequencing, must be employed in order to
support I-DPD. The uniqueness of a packet can then be identified by support I-DPD. The uniqueness of a packet can then be identified by
the [source IP address] of the packet originator, and the [sequence the source IP address of the packet originator and the sequence
number] (from the fragment header, hop-by-hop header option, or number (from the fragment header, hop-by-hop header option, or
IPsec). By doing so, each intermediate router can keep a record of IPsec). By doing so, each intermediate router can keep a record of
recently received packets, and determine whether the incoming packet recently received packets and determine whether the incoming packet
has been received or not. has been received or not.
4.2.1. Pre-activation Attacks (Pre-Play) 4.2.1. Pre-activation Attacks (Pre-Play)
In a wireless environment, or across any other shared channel, a In a wireless environment, or across any other shared channel, a
compromised SMF router can perceive the identification tuple [source compromised SMF router can perceive the identification tuple (source
IP address, sequence number] of a packet. It is possible to generate IP address, sequence number) of a packet. It is possible to generate
packet with the same [source IP address, sequence number] pair with a packet with the same (source IP address, sequence number) pair with
invalid content. If sequence number progression is predictable, then invalid content. If sequence number progression is predictable, then
it is trivial to generate and inject invalid packets with "future" it is trivial to generate and inject invalid packets with "future"
identification information into the network. If these invalid identification information into the network. If these invalid
packets arrive before the legitimate packets that they're spoofing, packets arrive before the legitimate packets that they are spoofing,
the latter will be treated as a duplicates and discarded. This can the latter will be treated as a duplicate and discarded. This can
prevent multicast packets from reaching parts of the network. prevent multicast packets from reaching parts of the network.
Figure 2 gives an example of pre-activation attack. A, B, and C are Figure 2 gives an example of pre-activation attack. A, B and C are
legitimate SMF routers, and X is the compromised SMF router. The legitimate SMF routers, and X is the compromised SMF router. The
line between the routers presents the packet forwarding. Router A is line between the routers presents the packet forwarding. Router A is
the source and originates a multicast packet with sequence number n. the source and originates a multicast packet with sequence number n.
When router X receives the packet, it generates an invalid packet When router X receives the packet, it generates an invalid packet
with the the source address of A, and sequence number n. If the with the source address of A and sequence number n. If the invalid
invalid packet arrives at router C before the forwarding of router B, packet arrives at router C before the forwarding of router B, the
the valid packet will be dropped by C as duplicate packet. An valid packet will be dropped by C as a duplicate packet. An attacker
attacker can manipulate jitter to make sure that the invalid packets can manipulate jitter to make sure that the invalid packets arrive
arrive first. Router X can even generate packet with future sequence first. Router X can even generate packets with future sequence
numbers (if they are predictable), so that the future legitimate numbers (if they are predictable), so that the future legitimate
packets with the same sequence numbers will be dropped as duplicate packets with the same sequence numbers will be dropped as duplicate
ones. ones.
.---. .---.
| X | | X |
--'---' __ --'---' __
packet with seq=n / \ invalid packet with seq=n packet with seq=n / \ invalid packet with seq=n
/ \ / \
.---. .---. .---. .---.
| A | | C | | A | | C |
'---' '---' '---' '---'
packet with seq=n \ .---. / packet with seq=n \ .---. /
\-- | B |__/ valid packet with seq=n \-- | B |__/ valid packet with seq=n
'---' '---'
Figure 2 Figure 2
As SMF currently does not have any timestamp mechanisms to protect As SMF currently does not have any timestamp mechanisms to protect
data packets, there is no viable way to detect such pre-play attacks data packets, there is no viable way to detect such pre-play attacks
by timestamp. Especially, if the attack is based on manipulation of by way of timestamps. Especially, if the attack is based on
jitter, the timestamp would not be effective because the timing is manipulation of jitter, the validation of timestamp would not be
still valid (but with much less value). helpful because the timing is still valid (but with much less value).
4.2.2. De-activation Attacks (Sequence Number wrangling) 4.2.2. De-activation Attacks (Sequence Number wrangling)
A compromised SMF router can also seek to de-activate DPD, by A compromised SMF router can also seek to de-activate DPD, by
modifying the sequence number in packets that it forwards. Thus, modifying the sequence number in packets that it forwards. Thus,
routers will not be able to detect an actual duplicate packet as a routers will not be able to detect an actual duplicate packet as a
duplicate - rather, they will treat them as new packets, i.e., duplicate - rather, they will treat them as new packets, i.e.,
process and forward them. This is similar to DoS attack. The process and forward them. This is similar to DoS attacks. The
consequence of this attack is an increased channel load, the origin consequence of this attack is an increased channel load, the origin
of which appears to be a router other than the compromised SMF of which appears to be a router other than the compromised SMF
router. router.
Given the topology shown in Figure 2, on receiving packet with seq=n, Given the topology shown in Figure 2, on receiving a packet with
the attacker X can forward the packet with modified sequence number seq=n, the attacker X can forward the packet with modified sequence
n+i. This has two consequences: firstly, router C will not be able number n+i. This has two consequences: firstly, router C will not be
to detect the packet forwarded by X is a duplicate packet; secondly, able to detect the packet forwarded by X is a duplicate packet;
the consequent packet with seq=n+i generated by router A probably secondly, the consequent packet with seq=n+i generated by router A
will be treated as duplicate packet, and dropped by router C. probably will be treated as duplicate packet, and dropped by router
C.
4.3. Threats to Hash-based Duplicate Packet Detection 4.3. Threats to Hash-based Duplicate Packet Detection
When it is not feasible to have explicit sequence numbers in packet When it is not feasible to have explicit sequence numbers in packet
headers, hash-based DPD can be used. A hash of the non-mutable headers, hash-based DPD can be used. A hash of the non-mutable
fields in the header of and the data payload can be generated, and fields in the header of and the data payload can be generated, and
recorded at the intermediate routers. A packet can thus be uniquely recorded at the intermediate routers. A packet can thus be uniquely
identified by the source IP address of the packet, and its hash- identified by the source IP address of the packet and its hash-value.
value.
The hash algorithm used by SMF is being applied only to provide a The hash algorithm used by SMF is being applied only to provide a
reduced probability of collision and is not being used for reduced probability of collision and is not being used for
cryptographic or authentication purposes. Consequently, a digest cryptographic or authentication purposes. Consequently, a digest
collision is still possible. In case the source router or gateway collision is still possible. In case the source router or gateway
identifies that it recently has generated or injected a packet with identifies that it recently has generated or injected a packet with
the same hash-value, it inserts a "Hash-Assist Value (HAV)" IPv6 the same hash-value, it inserts a "Hash-Assist Value (HAV)" IPv6
header option into the packet, such that calculating the hash also header option into the packet, such that calculating the hash also
over this HAV will render the resulting value unique. over this HAV will render the resulting value unique.
4.3.1. Attack on Hash-Assistant Value 4.3.1. Attack on Hash-Assistant Value
The HAV header is helpful when a digest collision happens. However, The HAV header is helpful when a digest collision happens. However,
it also introduces a potential vulnerability. As the HAV option is it also introduces a potential vulnerability. As the HAV option is
only added when the source or the ingressing SMF router detects that only added when the source or the ingress SMF router detects that the
the coming packet has digest collision with previously generated coming packet has digest collision with previously generated packets,
packets, it actually can be regarded as a "flag" of potential digest it actually can be regarded as a "flag" of potential digest
collision. A compromised SMF router can discover the HAV header, and collision. A compromised SMF router can discover the HAV header, and
be able to conclude a hash collision is possible if the HAV header is be able to conclude that a hash collision is possible if the HAV
removed. By doing so, other SMF routers receiving the modified header is removed. By doing so, the modified packet received by
packet will be treated as duplicate packet, and be dropped because it other SMF routers will be treated as duplicate packets, and be
has the same hash value with precedent packet. dropped because they have the same hash value with the precedent
packet.
In the example of Figure Figure 3, Router A and B are legitimate SMF In the example of Figure 3, Router A and B are legitimate SMF
routers, X is a compromised SMF router. A generate two packets P1 routers; X is a compromised SMF router. A generates two packets P1
and P2, with the same hash value h(P1)=h(P2)=x. Based on SMF and P2, with the same hash value h(P1)=h(P2)=x. Based on the SMF
specification, a hash-assistant value (HAV) is added to the latter specification, a hash-assistant value (HAV) is added to the latter
packet P2, so that h(P2+HAV)=x', to avoid digest collision. When the packet P2, so that h(P2+HAV)=x', to avoid digest collision. When the
attacker X detects the HAV of P2, it is able to conclude that a attacker X detects the HAV of P2, it is able to conclude that a
collision is possible by removing the HAV header. By doing so, collision is possible by removing the HAV header. By doing so,
packet P2 will be treated as duplicate packet by router B, and be packet P2 will be treated as duplicate packet by router B, and be
dropped. dropped.
P2 P1 P2 P1 P2 P1 P2 P1
.---. h(P2+HAV)=x' h(P1)=x .---. h(P2)=x h(P1)=x .---. .---. h(P2+HAV)=x' h(P1)=x .---. h(P2)=x h(P1)=x .---.
| A |---------------------------> | X | ----------------------> | B | | A |---------------------------> | X | ----------------------> | B |
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An SMF Router select itself as a relay, if: An SMF Router select itself as a relay, if:
o The SMF Router has a higher priority than all of its symmetric o The SMF Router has a higher priority than all of its symmetric
neighbors, or neighbors, or
o There does not exist a path from the neighbor with largest o There does not exist a path from the neighbor with largest
priority to any other neighbor, via neighbors with greater priority to any other neighbor, via neighbors with greater
priority. priority.
A Compromised SMF Router can disrupt the E-CDS algorithm by link A compromised SMF Router can disrupt the E-CDS algorithm by link
spoofing or identity spoofing. spoofing or identity spoofing.
5.2.1. Link Spoofing 5.2.1. Link Spoofing
Link spoofing implies that a Compromised SMF Router advertises non- Link spoofing implies that a compromised SMF Router advertises non-
existing links to another router (present in the network or not). existing links to another router (present in the network or not).
A Compromised SMF Router can declare itself with high route priority, A compromised SMF Router can declare itself with high route priority,
and spoofs the links to as many Legitimate SMF Routers as possible to and spoofs the links to as many legitimate SMF Routers as possible to
declare high connectivity. By doing so, it can prevent Legitimate declare high connectivity. By doing so, it can prevent legitimate
SMF Routers from self-selecting as relays. As the "super" relay in SMF Routers from self-selecting as relays. As the "super" relay in
the network, the Compromised SMF Router can manipulate the traffic the network, the compromised SMF Router can manipulate the traffic
relayed by it. relayed by it.
5.2.2. Identity Spoofing 5.2.2. Identity Spoofing
Identity spoofing implies that a compromised SMF router determines Identity spoofing implies that a compromised SMF router determines
and makes use of the identity of other legitimate routers, without and makes use of the identity of other legitimate routers, without
being authorised to do so. The identity of other routers can be being authorized to do so. The identity of other routers can be
obtained by overhearing the control messages or source/destination obtained by overhearing the control messages or the source/
address from datagram. The compromised SMF router can then generate destination address from datagrams. The compromised SMF router can
control or datagram traffic, pretending to be a legitimate router. then generate control or datagram traffic, pretending to be a
legitimate router.
Because E-CDS self-selection is based on the router priority value, a Because E-CDS self-selection is based on the router priority value, a
compromised SMF router can spoof the identity of other legitimate compromised SMF router can spoof the identity of other legitimate
routers, and declares a different router priority value. If it routers, and declares a different router priority value. If it
declares a higher priority of a spoofed router, it can prevent other declares a higher priority of a spoofed router, it can prevent other
routers from selecting themselves as relays. On the other hand, if routers from selecting themselves as relays. On the other hand, if
the compromised router declares lower priority of a spoofed router, the compromised router declares lower priority of a spoofed router,
it can enforces other routers to selecting themselves as relays, to it can enforce other routers to selecting themselves as relays, to
degrade the multicast forwarding to classical flooding. degrade the multicast forwarding to classical flooding.
5.3. Threats to S-MPR Algorithm 5.3. Threats to S-MPR Algorithm
The source-based multipoint relay (S-MPR) set selection algorithm The source-based multipoint relay (S-MPR) set selection algorithm
enables individual routers, using 2-hop topology information, to enables individual routers, using 2-hop topology information, to
select relays from their set of neighboring routers. MPRs are select relays from their set of neighboring routers. MPRs are
selected so that forwarding to the router's complete 2-hop neighbor selected so that forwarding to the router's complete 2-hop neighbor
set is covered. set is covered.
An SMF router forwards a multicast packet if and only if: An SMF router forwards a multicast packet if and only if:
o the packet is not received before, and o the packet has not been received received before, and
o the neighbor from which the packet was received has selected the o the neighbor from which the packet was received has selected the
router as MPR. router as MPR.
Because MPR calculation is based on the willingness declared by the Because MPR calculation is based on the willingness declared by the
SMF routers, and the connectivity of the routers, it can be disrupted SMF routers, and the connectivity of the routers, it can be disrupted
by both link spoofing and identity spoofing. The threats and its by both link spoofing and identity spoofing. The threats and its
impacts have been illustrated in section 5.1 of [RFC7186]. impacts have been illustrated in section 5.1 of [RFC7186].
5.4. Threats to MPR-CDS Algorithm 5.4. Threats to MPR-CDS Algorithm
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to MPR-CDS also. to MPR-CDS also.
6. Future Work 6. Future Work
Neither [RFC6621] nor this document propose mechanisms to secure the Neither [RFC6621] nor this document propose mechanisms to secure the
SMF protocol. However, this section aims at discussing possibilities SMF protocol. However, this section aims at discussing possibilities
to secure the protocol in the future and driving new work by to secure the protocol in the future and driving new work by
suggesting which threats discussed in the previous sections could be suggesting which threats discussed in the previous sections could be
addressed. addressed.
For I-PDP mechanism, employing randomized packet sequence number can For the I-DPD mechanism, employing randomized packet sequence numbers
avoid some pre-activation attacks based on sequence number can avoid some pre-activation attacks based on sequence number
prediction. If predicable sequence number has to be used, applying prediction. If predicable sequence numbers have to be used, applying
timestamps can mitigate pre-activation attacks. timestamps can mitigate pre-activation attacks.
If NHDP is used as the neighborhood discovery protocol, [RFC7183] is If NHDP is used as the neighborhood discovery protocol, [RFC7183] is
recommended to be implemented to enable integrity protection to NHDP, recommended to be implemented to enable integrity protection to NHDP,
which can help mitigating the threats related to identity spoofing which can help mitigating the threats related to identity spoofing
through the exchange of HELLO messages. through the exchange of HELLO messages.
[RFC7183] provides certain protection against identity spoofing by [RFC7183] provides certain protection against identity spoofing by
admitting only trusted routers to the network using Integrity Check admitting only trusted routers to the network using Integrity Check
Values (ICVs) in HELLO messages. However, using ICVs does not Values (ICVs) in HELLO messages. However, using ICVs does not
address the problem of compromised routers that can generate valid address the problem of compromised routers that can generate valid
ICVs. Detecting such compromised routers could be studied in new ICVs. Detecting such compromised routers could be studied in new
work. [RFC7183] mandates implementation of a security mechanism that work. [RFC7183] mandates implementation of a security mechanism that
is based on shared keys and makes excluding single compromised is based on shared keys and makes excluding single compromised
routers difficult. Work could be done to facilitate revocation routers difficult. Work could be done to facilitate revocation
mechanisms in certain MANET use cases where routers have sufficient mechanisms in certain MANET use cases where routers have sufficient
capabilities to support asymmetric keys (such as capabilities to support asymmetric keys (such as
[I-D.ietf-manet-ibs]) . [I-D.ietf-manet-ibs]).
As [RFC7183] does not protect the integrity of the multicast As [RFC7183] does not protect the integrity of the multicast
datagram, and no mechanism is specified to do that for SMF yet, the datagram, and no mechanism is specified to do that for SMF yet, the
duplicate packet detection is still vulnerable to the threats duplicate packet detection is still vulnerable to the threats
introduced in Section 4. introduced in Section 4.
If pre-activation/de-activation attacks and attack on hash-assistant If pre-activation/de-activation attacks and attack on hash-assistant
value of the multicast datagrams are to be mitigated, a datagram- value of the multicast datagrams are to be mitigated, a datagram-
level integrity protection mechanism is desired, by taking level integrity protection mechanism is desired, by taking
consideration of the identity field or hash-assistant value. consideration of the identity field or hash-assistant value.
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Thomas Heide Clausen Thomas Heide Clausen
LIX, Ecole Polytechnique LIX, Ecole Polytechnique
91128 Palaiseau Cedex, 91128 Palaiseau Cedex,
France France
Phone: +33 6 6058 9349 Phone: +33 6 6058 9349
Email: T.Clausen@computer.org Email: T.Clausen@computer.org
URI: http://www.thomasclausen.org/ URI: http://www.thomasclausen.org/
Ulrich Herberg Ulrich Herberg
Fujitsu Laboratories of America
1240 E Arques Ave
Sunnyvale, CA 94085
USA
Email: ulrich@herberg.name Email: ulrich@herberg.name
URI: http://www.herberg.name/ URI: http://www.herberg.name/
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