Internet DRAFT - draft-yi-manet-smf-sec-threats
draft-yi-manet-smf-sec-threats
Mobile Ad hoc Networking (MANET) J. Yi
Internet-Draft T. Clausen
Intended status: Informational LIX, Ecole Polytechnique
Expires: January 5, 2015 U. Herberg
Fujitsu Laboratories of America
July 4, 2014
Security Threats for Simplified Multicast Forwarding (SMF)
draft-yi-manet-smf-sec-threats-00
Abstract
This document analyzes security threats of the Simplified Multicast
Forwarding (SMF), including the vulnerabilities of duplicate packet
detection and relay set selection mechanisms. This document is not
intended to propose solutions to the threats described.
Status of this Memo
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SMF Threats Overview . . . . . . . . . . . . . . . . . . . . . 4
4. Threats to Duplicate Packet Detection . . . . . . . . . . . . 5
4.1. Threats to Identification-based Duplicate Packet
Detection . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1.1. Pre-activation Attacks (Pre-Play) . . . . . . . . . . 6
4.1.2. De-activation Attacks (Sequence Number wrangling) . . 6
4.2. Threats to Hash-based Duplicate Packet Detection . . . . . 7
4.2.1. Replay Attack . . . . . . . . . . . . . . . . . . . . 7
4.2.2. Attack on Hash-Assistant Value . . . . . . . . . . . . 8
5. Threats to Relay Set Selection . . . . . . . . . . . . . . . . 8
5.1. Relay Set Selection Common Threats . . . . . . . . . . . . 9
5.2. Threats to E-CDS Algorithm . . . . . . . . . . . . . . . . 9
5.2.1. Link Spoofing . . . . . . . . . . . . . . . . . . . . 9
5.2.2. Identity Spoofing . . . . . . . . . . . . . . . . . . 9
5.3. Threats to S-MPR Algorithm . . . . . . . . . . . . . . . . 10
5.4. Threats to MPR-CDS Algorithm . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
This document analyzes security threats of the Simplified Multicast
Forwarding (SMF) mechanism [RFC6621]. SMF aims at providing basic
Internet Protocol (IP) multicast forwarding, in a way which is
suitable for limited wireless mesh and Mobile Ad hoc NETworks
(MANET). SMF is constituted of two major functional components:
Duplicate Packet Detection and Relay Set Selection.
SMF is typically used in decentralized wireless environments, and is
potentially exposed to different kinds of attacks and
misconfigurations. Some of the threats are of particular
significance as compared to wired networks. In [RFC6621], SMF does
not define any explicit security measures for protecting the
integrity of the protocol.
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
deployments may be suitable to deploy common IP protection mechanisms
(e.g., because of limited resources of MANET routers to support the
IPsec stack). The document analyzes possible attacks on and mis-
configurations of SMF and outlines the consequences of such attacks/
mis-configurations to the state maintained by SMF in each router
(and, thus, made available to protocols using this state).
This document aims at analyzing and describing the potential
vulnerabilities of and attack vecors for SMF. While completeness in
such an analysis always is a goal, no claims of being complete are
made. The goal of this document is to be helpful for when deploying
SMF in a network and needing to understand the risks thereby incurred
- as wll as for providing a reference and documented experience with
SMF as input for possibly future developments of SMF.
This document is not intended to propose solutions to the threats
described. [RFC7182] provides a framework, which can be used with
SMF, and which - depending on how it is used - may offer some degree
of protection against the threats described in this document related
to identity spoofing.
2. Terminology
This document uses the terminology and notation defined in [RFC2119],
[RFC5444], [RFC6621] and [RFC4949].
Additionally, this document introduces the following terminology:
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SMF router: A MANET router, running SMF as specified in [RFC6621].
Attacker: A device that is present in the network and intentionally
seeks to compromise the information bases in SMF routers.
Compromised SMF router: An attacker, present in the network and
which generates syntactically correct SMF control messages.
Control messages emitted by a compromised SMF router may contain
additional information, or omit information, as compared to a
control message generated by a non-compromized SMF router located
in the same topological position in the network.
Legitimate SMF router: An SMF router, which is not a compromised SMF
Router.
3. SMF Threats Overview
SMF requires an external dynamic neighborhood discovery mechanism in
orde to maintain suitable topological information describing its
immediate neighborhood, and thereby allowing it to select reduced
relay sets for forwarding multicast data traffic. Such an external
dynamic neighborhood discovery mechanism MAY be provided by lower-
layer interface information, by a concurrently operating MANET
routing protocol which already maintains such information such as
[RFC7181], or by explicitly using MANET Neighborhood Discovery
Protocol (NHDP) [RFC6130]. If NHDP is used for neighborhood
discovery by SMF, SMF implicitly inherits the vulnerabilities of
NHDP, as discussed in [RFC7186]. This document assumes that NHDP is
used.
Based on neighborhood discovery mechanisms, SMF specified two major
functional components: Duplicate Packet Detection (DPD) and Relay Set
Selection (RSS).
DPD is required by SMF in order to be able to detect duplicate
packets and eliminate their redundant forwarding. An Attacker has
several ways in which to harm the DPD mechanisms:
o It can "deactivate" DPD, so as to make it such that duplicate
packets are not correctly detected, and that as a consequence they
are (redundantly) transmitted, increasing the load on the network,
draing the batteries of the routers involved, etc.
o It can "pre-activate" DPD, so as to make DPD detect a later
arriving (valid) packet as being a duplicate, which therefore
won't be forwarded"
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The attacks on DPD are detailed in Section 4.
RSS produces a reduced relay set forforwarding multicast data packets
across the MANET. SMF supports the use of several relay set
algorithms, including E-CDS (Essential Connected Dominating Set),
S-MPR (Source-based Multi-point Relay, as known from [RFC3626] and
[RFC7181]), or MPR-CDS. An Attacker can disrupt the RSS algorithm,
by degrading it to classical flooding, or by "masking" certain part
of the routers from the multicasting domain. The attacks to RSS
algorithms are illustrated in Section 5.
4. Threats to Duplicate Packet Detection
Duplicate Packet Detection (DPD) is required for packet dissemination
in MANET because the packets may be transmitted via the same physical
interface as the one over which they were received. A router may
also receive multiple copies of the same packets from different
neighbors. DPD is thus used to check if an incoming packet has been
received or not.
DPD is achieved by a router maintaining a record of recently
processed multicast packets, and comparing later received multicast
herewith. A duplicate packet detected is silently dropped, and is
not inserted into the forwarding path of that router, nor is it
delivered to an application. DPD, as proposed by SMF, supports both
IPv4 and IPv6 and for each suggests two duplicate packet detection
mechanisms: 1) header content identification-based DPD (I-DPD), using
packet headers, in combination with flow state, to estimate temporal
uniqueness of a packet, and 2) hash-based DPD (H-DPD), employing
hashing of selected header fields and payload for the same effect.
As they are distinct mechanisms, the threats to I-DPD and H-DPD are
discussed separately.
4.1. Threats to Identification-based Duplicate Packet Detection
I-DPD uses a specific DPD identifier in the packet header to identify
a packet. By default, such packet identification is not provided by
the IP packet header (for both IPv4 and IPv6). Therefore, additional
identification header, such as the fragment header, a hop-by-hop
header option, or IPSec sequencing, must be employed in order to
support I-DPD. The uniqueness of a packet can then be identified by
the [source IP address] of the packet originator, and the [sequence
number] (from the fragment header, hop-by-hop header option, or
IPsec). By doing so, each intermediate router can keep a record of
recently received packet, and determine the coming packet has been
received or not.
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4.1.1. Pre-activation Attacks (Pre-Play)
In a wireless environment, or across any other shared channel, a
compromised SMF router can perceive the identification tuple [source
IP, sequence number] of a packet. If sequence number progression is
predictable, then it is trivial to generate aand inject invalid
packets with "future" identification information into the network.
If these invalid packets arrive before the legitimate packets that
they're spoofing, the latter will be treated as a duplicates and
discarded. This can prevent multicast packets from reaching parts of
the network.
Figure 1 gives an example of pre-activation attack. A, B, and C are
legitimate SMF routers, and X is the compromised SMF router. The
line between the routers presents the packet forwarding. Router A is
the source and originates a multicast packet with sequence number n.
When router X receives the packet, it generates an invalid packet
with the the source address of A, and sequence number n. If the
invalid packet arrives at router C before the forwarding of router B,
the valid packet will be dropped by C as duplicate packet. In a
wireless environment, jitter is commonly used to avoid systematic
collisions at MAC layer [RFC5148], thus an attacker can increase the
probability that its invalid packets arrive first by retransmitting
them without jittering.
.---.
| X |
--'---' __
packet with seq=n / \ invalid packet with seq=n
/ \
.---. .---.
| A | | C |
'---' '---'
packet with seq=n \ .---. /
\-- | B |__/ valid packet with seq=n
'---'
Figure 1
4.1.2. De-activation Attacks (Sequence Number wrangling)
A compromised SMF router can also seek to de-activate DPD, by
modifying the sequence number in packets that it forwards. Thus,
routers will not be able to detect an actual duplicate packet as a
duplicate - rather, they will treat them as new packets, i.e.,
process and forward them. This is similar to DoS attack. The
consequence of this attack is an increased channel load, the origin
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of which appears to be a router other than the compromised SMF
router.
Given the topology shown in Figure 1, on receiving packet with seq=n,
the attacker X can forward the packet with modified sequence number
n+i. This has two consequences: firstly, router C will not be able
to detect the packet forwarded by X is a duplicate packet; secondly,
the consequent packet with seq=n+i generated by router A probably
will be treated as duplicate packet, and dropped by router C.
4.2. Threats to Hash-based Duplicate Packet Detection
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
fields in the header of and the data payload can be generated, and
recorded at the intermediate routers. A packet can thus be uniquely
identified by the source IP address of the packet, and its hash-
value.
The hash algorithm used by SMF is being applied only to provide a
reduced probability of collision and is not being used for
cryptographic or authentication purposes. Consequently, a digest
collision is still possible. In case the source router or gateway
identifies that it recently has generated or injected a packet with
the same hash-value, it inserts a "Hash-Assist Value (HAV)" IPv6
header option into the packet, such that calculating the hash also
over this HAV will render the resulting value unique.
4.2.1. Replay Attack
A replay attack implies that control traffic from one region of the
network is recorded and replayed in a different region at (almost)
the same time, or in the same region at a different time.
One possible replay attack is based on the Time-to-Live (TTL, for
IPv4) or hop limit (for IPv6) field. As routers only forward packets
with TTL > 1, a compromised SMF router can forward an otherwise valid
packet, while drastically reducing the TTL hereof. This will inhibit
recipient routers from later forwarding the same multicast packet,
even if received with a different TTL - essentially a compromised SMF
router thus can instruct its neighbors to block forwarding of valid
multicast packets. As the TTL of a packet is intended to be
manipulated by intermediaries forwarding it, classic methods such as
integrity check values (e.g., digital signatures) are typically
calculated with setting TTL fields to some pre-determined value
(e.g., 0) - such is for example the case for IPsec Authentication
Headers - rendering such an attack more difficult to both detect and
counter. If the compromised SMF router has access to a "wormhole"
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through the network (a directional antenna, a tunnel to a
collaborator or a wired connection, allowing it to bridge parts of a
network otherwise distant) it can make sure that the packets with
such an artificially reduced TTL arrive before their unmodified
counterparts.
4.2.2. Attack on Hash-Assistant Value
The HAV header is helpful when a digest collision happens. However,
it also introduces a potential vulnerability. As the HAV option is
only added when the source or the ingressing SMF router detects that
the coming packet has digest collision with previously generated
packets, it actually can be regarded as a "flag" of potential digest
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
removed. By doing so, other SMF routers receiving the modified
packet will be treated as duplicate packet, and be dropped because it
has the same hash value with precedent packet.
In the example of Figure Figure 2, Router A and B are legitimate SMF
routers, X is a compromised SMF router. A generate two packets P1
and P2, with the same hash value h(P1)=h(P2)=x. Based on SMF
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
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,
packet P2 will be treated as duplicate packet by router B, and be
dropped.
P2 P1 P2 P1
.---. h(P2+HAV)=x' h(P1)=x .---. h(P2)=x h(P1)=x .---.
| A |---------------------------> | X | ----------------------> | B |
`---' `---' `---'
Figure 2
5. Threats to Relay Set Selection
A framework for RSS mechanism, rather than a specific RSS algorithm
is provided by SMF. It is normally achieved by distributed
algorithms that can dynamically generate a topological Connected
Dominating Set based on 1-hop and 2-hop neighborhood information. In
this section, the common threats to the RSS framework are first
discussed. Then the three commonly used algorithms: Essential
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Connection Dominating Set (E-CDS) algorithm, Source-based Multipoint
Relay (S-MPR) and Multipoint Relay Connected Dominating Set (MPR-CDS)
are analyzed.
5.1. Relay Set Selection Common Threats
The common threats to RSS algorithms, including Denial of Service
attack, eavesdropping, message timing attack and broadcast storm have
been discussed in [RFC7186].
5.2. Threats to E-CDS Algorithm
The "Essential Connected Dominating Set" (E-CDS) algorithm [RFC5614]
forms a single CDS mesh for the SMF operating region. It requires
2-hop neighborhood information (the identify of the neighbors, the
link to the neighbors and neighbors' priority information) collected
through NHDP or another process.
An SMF Router select itself as a relay, if:
o The SMF Router has a higher priority than all of its symmetric
neighbors, or
o There does not exist a path from the neighbor with largest
priority to any other neighbor, via neighbors with greater
priority.
A Compromised SMF Router can disrupt the E-CDS algorithm by link
spoofing or identity spoofing.
5.2.1. Link Spoofing
Link spoofing implies that a Compromised SMF Router advertises non-
existing links to another router (present in the network or not).
A Compromised SMF Router can declare itself with high route priority,
and spoofs the links to as many Legitimate SMF Routers as possible to
declare high connectivity. By doing so, it can prevent Legitimate
SMF Routers from self-selecting as relays. As the "super" relay in
the network, the Compromised SMF Router can manipulate the traffic
relayed by it.
5.2.2. Identity Spoofing
Identity spoofing implies that a compromised SMF router determines
and makes use of the identity of other legitimate routers, without
being authorised to do so. The identity of other routers can be
obtained by overhearing the control messages or source/destination
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address from datagram. The compromised SMF router can 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
compromised SMF router can spoof the identity of other legitimate
routers, and declares a different router priority value. If it
declares a higher priority of a spoofed router, it can prevent other
routers from selecting themselves as relays. On the other hand, if
the compromised router declares lower priority of a spoofed router,
it can enforces other routers to selecting themselves as relays, to
degrade the multicast forwarding to classical flooding.
5.3. Threats to S-MPR Algorithm
The source-based multipoint relay (S-MPR) set selection algorithm
enables individual routers, using 2-hop topology information, to
select relays from their set of neighboring routers. MPRs are
selected so that forwarding to the router's complete 2-hop neighbor
set is covered.
An SMF router forwards a multicast packet if and only if:
o the packet is not received before, and
o the neighbor from which the packet was received has selected the
router as MPR.
Because MPR calculation is based on the willingness declared by the
SMF routers, and the connectivity of the routers, it can be disrupted
by both link spoofing and identity spoofing. The threats and its
impacts have been illustrated in section 5.1 of [RFC7186].
5.4. Threats to MPR-CDS Algorithm
MPR-CDS is a derivative from S-MPR. The main difference between
S-MPR and MPR-CDS is that while S-MPR forms a different broadcast
tree for each source in the network, MPR-CDS forms a unique broadcast
tree for all sources in the network.
As MPR-CDS combines E-CDS and S-MPR, the vulnerabilities of E-CDS and
S-MPR that discussed in Section 5.2 and Section 5.3 apply to MPR-CDS
also.
6. Security Considerations
This document does not specify a protocol or a procedure. The
document, however, reflects on security considerations for SMF for
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packet dissemination in MANETs.
7. IANA Considerations
This document contains no actions for IANA.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET)
Extension of OSPF Using Connected Dominating Set (CDS)
Flooding", RFC 5614, August 2009.
[RFC6621] Macker, J., "Simplified Multicast Forwarding", RFC 6621,
May 2012.
[RFC7186] Yi, J., Herberg, U., and T. Clausen, "Security Threats for
the Neighborhood Discovery Protocol (NHDP)", RFC 7186,
April 2014.
8.2. Informative References
[RFC3626] Clausen, T. and P. Jacquet, "The Optimized Link State
Routing Protocol", RFC 3626, October 2003.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.
[RFC5148] Clausen, T., Dearlove, C., and B. Adamson, "Jitter
Considerations in Mobile Ad Hoc Networks (MANETs)",
RFC 5148, February 2008.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized MANET Packet/Message Format", RFC 5444,
February 2009.
[RFC6130] Clausen, T., Dean, J., and C. Dearlove, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, April 2011.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol version 2",
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RFC 7181, April 2014.
[RFC7182] Herberg, U., Clausen, T., and C. Dearlove, "Integrity
Check Value and Timestamp TLV Definitions for Mobile Ad
Hoc Networks (MANETs)", RFC 7182, April 2014.
Authors' Addresses
Jiazi Yi
LIX, Ecole Polytechnique
91128 Palaiseau Cedex,
France
Phone: +33 1 77 57 80 85
Email: jiazi@jiaziyi.com
URI: http://www.jiaziyi.com/
Thomas Heide Clausen
LIX, Ecole Polytechnique
91128 Palaiseau Cedex,
France
Phone: +33 6 6058 9349
Email: T.Clausen@computer.org
URI: http://www.thomasclausen.org/
Ulrich Herberg
Fujitsu Laboratories of America
1240 E Arques Ave
Sunnyvale, CA 94085
USA
Email: ulrich@herberg.name
URI: http://www.herberg.name/
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