Network Working Group D. Beard
Internet-Draft Nortel Networks
Expires: August 22, 2003 S. Murphy
Network Associates, Inc
Y. Yang
Cisco Systems
February 21, 2003
Generic Threats to Routing Protocols
draft-beard-rpsec-routing-threats-01.txt
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Abstract
Routing protocols are subject to attacks that can harm individual
users or the network operations as a whole. The lack of a common set
of security requirements has led to the use in existing routing
protocol of a variety of different security solutions, which provide
various levels of security coverage.
The RPSEC working group intends to deliver in a separate document a
set of security requirements for consideration of routing protocol
designers. The first step in developing the security requirements is
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to analyze the threats that face routing protocols. This document
describes the threats, including threat sources and capabilities,
threat actions, and threat consequences as well as a breakdown of
routing functions that might be separately attacked.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Routing Functions Overview . . . . . . . . . . . . . . . . . 4
2.1 Targeted Functions . . . . . . . . . . . . . . . . . . . . . 4
3. Threat Definitions . . . . . . . . . . . . . . . . . . . . . 6
3.1 Threat Sources . . . . . . . . . . . . . . . . . . . . . . . 6
3.2 Threat Actions . . . . . . . . . . . . . . . . . . . . . . . 7
3.3 Threat Consequences . . . . . . . . . . . . . . . . . . . . 8
3.3.1 Threat Consequence Zone . . . . . . . . . . . . . . . . . . 11
3.3.2 Threat Consequence Periods . . . . . . . . . . . . . . . . . 11
4. Generally Identifiable Routing Threats Actions . . . . . . . 12
4.1 Deliberate Exposure . . . . . . . . . . . . . . . . . . . . 12
4.2 Sniffing . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.3 Traffic Analysis . . . . . . . . . . . . . . . . . . . . . . 13
4.4 Spoofing . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5 Falsification . . . . . . . . . . . . . . . . . . . . . . . 15
4.5.1 Falsifications by Originators . . . . . . . . . . . . . . . 15
4.5.2 Falsifications by Forwarders . . . . . . . . . . . . . . . . 21
4.6 Interference . . . . . . . . . . . . . . . . . . . . . . . . 22
4.7 Overload . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.8 Byzantine Failures . . . . . . . . . . . . . . . . . . . . . 23
4.9 Discarding of Control Packets . . . . . . . . . . . . . . . 24
4.10 Network Mapping Threats . . . . . . . . . . . . . . . . . . 25
5. Multicast Routing Protocol Considerations . . . . . . . . . 26
6. Security Considerations . . . . . . . . . . . . . . . . . . 28
References . . . . . . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 29
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31
Intellectual Property and Copyright Statements . . . . . . . 32
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1. Introduction
The RPSEC working group is tasked to deliver a description of the
security requirements for routing protocols. This internet draft
discusses an analysis of the threats that face routing protocols, as
a precursor to developing a common set of security requirements for
routing protocols. Therefore, we intentionally do not address threats
to routers (hacking, denial of service flooding attacks, etc.) or to
specific routing protocol implementations (bugs, etc.). The security
requirements derived from this threat analysis are intended to be
guidance to those who are designing routing protocols.
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2. Routing Functions Overview
Routing protocols in general have several common functions:
o Transport Subsystem: The routing protocol transmits messages to
its peers using some underlying protocol. For some, as in OSPF,
this is IP. For others, this can be a broadcast link layer, as in
AODV. Still others may run over TCP. In many cases, the routing
protocol is subject to attacks on its underlying protocol.
o Neighbor State Maintenance: Each protocol has a different
mechanism for determining its peers in the routing topology. Some
protocols have distinct exchange through which they establish
peering relationships, e.g., Hello exchanges in OSPF. The peering
relationship formation is the first step of topology
determination. For protocols that maintain state about their
peering relationships, attacks that disrupt the peering
relationship can have widespread consequences. For example, if
the DR election is disrupted in an OSPF network, an unauthorized
router could be chosen as designated router. This might allow
unauthorized access to routing information. In BGP, if a router
receives a CEASE message, it can break the peering relationship
and cause any related topology information to be flushed.
o Database Maintenance: Routing protocols exchange network topology
and reachability information. The routers collect this
information in routing databases in varying detail. The
maintenance of these databases is a significant portion of the
function of a routing protocol. The information in the database
must be authentic and authorized; otherwise the function of
routing in the overall network is damaged. For example, if an
OSPF router sends LSA's with the wrong Advertising Router, the
receivers will compute a SPF tree that is incorrect and might not
forward the traffic. If a BGP router advertises a NLRI that it is
not authorized to advertise, then receivers might forward that
NLRI's traffic toward that router and the traffic would not be
deliverable. A PIM router might transmit a JOIN message to
receive multicast data it would otherwise not receive
2.1 Targeted Functions
Just as a router's functions can be divided into control and data
plane (protocol traffic vs. data traffic), so the routing protocol
has a control and a data plane. A routing protocol has some message
exchanges that are intended only for control of the protocol state.
This is the routing protocol control plane. Other message exchanges
are intended to distribute the information used to perform the
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forwarding function, whether that is to establish a forwarding table
in each router or to return a description of the route to use. This
is the routing protocol data plane. Each of the routing functions
may have both control and data aspects, but there will naturally be
an emphasis on one or the other. Neighbor maintenance is likely to
be focused on the routing protocol control plane aspects, for
example, while database maintenance may have more focus on the
routing protocol data plane aspects.
Both the control and the data plane are subject to attack. An
attacker who is able to target the routing protocol control plane so
as to break a neighbor (e.g., peering, adjacency) relationship can
have a strong effect on the behavior of routing in those routers and
likely the surrounding neighborhood. An attacker who is able to
break a database exchange between two routers can also affect routing
behavior. In the routing protocol data plane, an attacker who is
able to introduce bogus data can have a strong effect on the behavior
of routing in the neighborhood.
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3. Threat Definitions
Threat is defined in [SEC-GLOSS] as a potential for violation of
security, which exists when there is a circumstance, capability,
action, or event that could breach security and cause harm. A threat
presents itself when an attacker has the ability to take advantage of
an existing security weakness. Threats can be categorized based on
various rules, such as threat sources, threat actions, threat
consequences, threat consequence zones, and threat consequence
periods.
3.1 Threat Sources
Legitimate devices (routers) participate in the routing dialog and
computation, intended by the authoritative network administrator,
running correct and bug-free code, and using correct and bug-free
configuration information. -- By correct and bug-free configuration
information, we mean the configurations obey routing protocols and
are intended by the authoritative network administrator.
On the other hand, attackers may participate routing, not being
authorized, running incorrect codes, or using invalid configurations.
In general, attackers can be outsiders or insiders. An insider is an
authorized participant in the routing protocol. An outsider is any
other host or network. A host is determined to be an outsider or an
insider from the point of view of a particular router. Even an
authorized protocol speaker can be an outsider to a particular router
if the router does not consider the speaker to be a legitimate peer
(as could conceivably happen on a multi-access link).
Specifically, threats can be classified into four categories, based
on their sources [DV-SECURITY]:
o Threat from compromised links: A compromised link is where an
attacker can, somehow, access a physical medium and/or have some
control over the channel. This threat exists when there is no
access control mechanisms applied to physical mediums or channels,
or such mechanisms can be circumvented. The attacker may
eavesdrop, replay, delay, or drop routing messages, or break
routing sessions between authorized routers, without participating
in the routing exchange.
o Threats from compromised devices (e.g. routers): A compromised
device (router) is an authorized router with routing software
bugs, hardware defects, and / or incorrect/unintended
configurations. This threat takes place when there are no
mechanisms to verify a device's (router) system integrity, i.e.
the router is working correctly as been intended by the
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authoritative network administrator, or such mechanisms can be
circumvented. The attacker may inappropriately claim authority
for some network resources, or violate routing protocols, such as
advertising invalid routing information and etc.
o Threat from unauthorized devices (routers): An unauthorized device
(router) participates in routing exchange and computation, without
being authorized (explicitly or implicitly) from the authoritative
network administrator. This threat happens when there is no access
control mechanism applied to routing sessions/routing exchanges or
such mechanism can be circumvented. The attacker may gain
knowledge of the network topology through routing exchange, as
well as do anything that a compromised router can do.
o Threat from masquerading devices (routers): A masquerading device
(router) illegitimately assumes another router's identity. This
threat occurs when there are no (data origin or peer entity)
authentication mechanisms, or such mechanisms can be circumvented.
The attacker can do anything that an unauthorized router can do.
A device (router) can play multiple roles concurrently. A legitimate
OSPF router might be a masquerading RIP router, and a compromised
iBGP link might be a compromised OSPF router as well.
3.2 Threat Actions
A threat action is an assault on system security [SEC-GLOSS], which
could be an intentional behavior, or an accidental event.
The actions that might be used to attack routing protocols include:
o Masquerade: The attacker, whether insider or outsider, may adopt
the identity of a legitimate peer. (This is an attack against
origin authenticity.)
o Interception:The attacker gains access to routing information that
is considered sensitive. (This is an attack against
confidentiality, i.e., privacy.)
o Falsification: The attacker is able to substitute modified
messages for valid routing messages. (This is an attack against
integrity.)
o Misuse: The attacker is able to introduce unauthorized routing
information that disrupts routing behavior. (This is an attack
against authorized use.)
o Replay The attacker is able to re-introduce previously transmitted
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messages. (This is an attack against freshness.)
These attacks might be used by insider or outsider to accomplish any
of the compromises listed below.
3.3 Threat Consequences
A threat consequence is a security violation that results from a
threat action [SEC-GLOSS]. The compromise to the behavior of the
routing system can damage a particular network or host or can damage
the operation of the network as a whole.
Four types of threat consequences, disclosure, deception, disruption,
and usurpation, are identified in [SEC-GLOSS]. Specifically for
threats against routing protocols, these consequences can be
described as:
o Disclosure: Disclosure of routing information happens where a
router successfully accesses the information without being
authorized. Compromised links can cause disclosure, if routing
exchanges lack confidentiality. Compromised devices (routers),
unauthorized devices (routers), and masquerading devices (routers)
can always cause disclosure, as long as they are successfully
involved in the routing exchanges. Please note, although
disclosure of routing information can pose a security threat or be
part of a later, larger, or higher layer attack, confidentiality
is not generally a design goal of routing protocols.
o Deception: This consequence happens when a legitimate router
receives a false routing message and believes it to be true. All
attackers (Compromised links, compromised device (routers),
unauthorized devices (routers), and masquerading devices (routers)
can cause this consequence if the receiving router lacks ability
to check routing message integrity, routing message origin
authentication or peer router authentication.
o Disruption: This consequence occurs when a legitimate router's
operation is being interrupted or prevented. Subvert links can
cause this by replaying, delaying, or dropping routing messages,
or breaking routing sessions between legitimate routers.
Compromised devices (router), unauthorized devices (routers), and
masquerading device (routers) can cause this consequence by
sending false routing messages, interfering normal routing
exchanges, or flooding unnecessary messages. (DoS is a common
threat action causing disruption.)
o Usurpation: This consequence happens when an attacker gains
control over a legitimate router's services/functions. Compromised
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links can cause this by delaying or dropping routing exchanges, or
replaying out-dated routing information. Compromised routers,
unauthorized routers, and masquerading routers can cause this
consequence by sending false routing information, interfering
routing exchanges, or system integrity.
Note: an attacker does not have to directly control a router to
control its services. For example, in Figure 1, Network 1 is
dual-homed through Router A and Router B, and Router A is preferred.
However, Router B is compromised and advertises a lower metric.
Consequently, devices on the Internet choose the path through Router
B to reach Network 1. In this way, Router B steals the data traffic
and Router A surrenders its control of the services to Router B. This
depicted in Figure 1.
+-------------+ +-------+
| Internet |---| Rtr A |
+------+------+ +---+---+
| |
| |
| |
| *-+-*
+---+---+ / \
| Rtr B |------* N 1 *
+-------+ \ /
*---*
Figure 1
Also, several threat consequences might be caused by a single threat
action. In Figure 1, there exist at least two consequences:
routers using Router B to reach Network 1 are deceived, while Router
A is usurped.
Within the context of the threat consequences described above, damage
that might result from attacks against the network as a whole may
include:
o Network congestion: more data traffic is forwarded through some
portion of the network than would otherwise need to carry the
traffic,
o Blackhole: large amounts of traffic are directed to be forwarded
through one router that cannot handle the increased level of
traffic and drops many/most/all packets,
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o Looping: data traffic is forwarded along a route that loops, so
that the data is never delivered (resulting in network
congestion),
o Partition: some portion of the network believes that it is
partitioned from the rest of the network when it is not,
o Churn: the forwarding in the network changes (unnecessarily) at a
rapid pace, resulting in large variations in the data delivery
patterns (and adversely affecting congestion control techniques),
o Instability: the protocol becomes unstable so that convergence on
a global forwarding state is not achieved, and
o Overload: the protocol messages themselves become a significant
portion of the traffic the network carries.
The damage that might result from attacks against a particular host
or network address may include:
o Starvation: data traffic destined for the network or host is
forwarded to a part of the network that cannot deliver it,
o Eavesdrop: data traffic is forwarded through some router or
network that would otherwise not see the traffic, affording an
opportunity to see the data or at least the data delivery pattern,
o Cut: some portion of the network believes that it has no route to
the host or network when it is in fact connected,
o Delay: data traffic destined for the network or host is forwarded
along a route that is in some way inferior to the route it would
otherwise take,
o Looping: data traffic for the network or host is forwarded along a
route that loops, so that the data is never delivered,
It is important to consider all compromises, because some security
solutions can protect against one attack but not against others. It
might be possible to design a security solution that protected
against an attack that eavesdropped on one destination's traffic
without protecting against an attack that overwhelmed a router. Or
that prevented a starvation attack against one host, but not against
a net wide blackhole. The security requirements must be clear as to
which compromises are being avoided and which must be addressed by
other means (e.g., by administrative means outside the protocol).
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3.3.1 Threat Consequence Zone
A threat consequence zone covers an area within which the network
operations have been affected by the threat consequences. Possible
threat consequence zones can be classified as: a single link or
router, multiple routers (within a single routing domain), a single
routing domain, multiple routing domains, or the global Internet. The
threat consequence zone varies based on the threat action and origin.
Similar threat actions that happened at different locations may cause
totally different threat consequence zones. For example, when a
compromised link breaks the routing session between a distribution
router and a stub router, only reach ability from and to the network
devices attached on the stub router will be impaired. In other words,
the threat consequence zone is a single router. Nonetheless, if the
compromised router is located between a customer edge router and its
corresponding provider edge router, such an action might cause the
whole customer site to lose its connection. In this case, the threat
consequence zone might be a single routing domain.
3.3.2 Threat Consequence Periods
Threat consequence period is defined as a portion of time during
which the network operations have been impacted by the threat
consequences. The threat consequence period is influenced by, but not
totally dependent on the duration of the threat action. In some
cases, the network operations will get back to normal as soon as the
threat action has been stopped. In other cases, however, threat
consequences may appear longer than threat action. For example, in
the original ARPANET link-state algorithm, some errors in a router
might introduce three instances of an LSA, and all of them would be
flooded throughout the network forever, until the entire network was
power cycled [PROTO-VULN].
With appropriate security detection facilities, the network might
detect the threat action, implement countermeasures, and resume
normal operations even before the threat action has been stopped. In
this documentation, we assume such facilities do not exist.
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4. Generally Identifiable Routing Threats Actions
This section addresses generally identifiable and recognized threat
action against routing protocols. The threats are not necessarily
specific to individual protocols but may be present in one or more of
the common routing protocols in use today.
4.1 Deliberate Exposure
Deliberate Exposure is defined as an intentional action that
attackers employ to release routing information directly to other
routers. This definition presumes that the receiving routers are not
authorized to access the routing information. However, an exposure is
different from a deliberate exposure. While the deliberate exposure
is always a threat action, the exposure is not. Routing protocols are
designed to expose routing information. A legitimate router should
always expose routing information to its legitimate peers. In some
cases, a legitimate router may expose routing information to peering
unauthorized/masquerading routers, if it is deceived. However, there
is no reason that a legitimate router should keep exposing correct
routing information to its peers when those peers have been
determined to be unauthorized or masquerading entities.
The consequence of deliberate exposure is the disclosure of routing
information.
The threat consequence zone of deliberate exposure depends on the
routing information that the attackers have exposed. The more
knowledge they have exposed, the bigger the threat consequence zone.
The threat consequence period of deliberate exposure might be longer
than the duration of the action itself. The routing information
exposed will not be out-dated until there is a topology change of the
exposed network.
4.2 Sniffing
Sniffing is an action whereby attackers monitor and/or record the
routing exchanges between authorized routers. Compromised links can
sniff the links over which they have control. (Compromised routers,
unauthorized routers, and masquerading routers can sniff, but do not
need to do this, to access the routing information. They can learn
the routing information as long as they are successfully involved in
the routing exchanges).
The consequence of sniffing is disclosure of routing information.
The threat consequence zone of sniffing depends on the attacker's
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location, the routing protocol type, and, ultimately, what routing
information has been recorded. For example, if the compromised link
were located in an OSPF totally stubby area, the threat consequence
zone should be limited to the whole area. Or, the compromised link
could gain knowledge of multiple routing domains, if it sniffs an
eBGP session between two providers.
The threat consequence period might be longer than the duration of
the action. After the compromised link stops sniffing, its knowledge
will not be out-dated until there is a topology change of the
disclosed network.
4.3 Traffic Analysis
Traffic analysis is action whereby attackers gain routing information
by analyzing the characteristics of the data traffic. Compromised
links can analyze the data traffic over the links where they have
control. (Compromised routers, unauthorized routers, and masquerading
routers do not need to do this, although they can, to access the
routing information. They learn the routing information by being
successfully involved in the routing exchanges).
The consequence of data traffic analysis is the disclosure of routing
information. For example, the source and destination IP address of
the data traffic, the type, magnitude, and volume of traffic is
disclosed.
The threat consequence zone of the traffic analysis depends on the
attacker's location and, ultimately, what data traffic has flown
through. A compromised link at the network core should be able to
gain more information than its counterpart at the edge.
The threat consequence period might be longer than the duration of
the traffic analysis. After the attacker stops traffic analysis, its
knowledge will not be out-dated until there is a topology change of
the disclosed network.
4.4 Spoofing
A spoofing is defined as an action whereby an attacker participates
in the routing computation and exchanges with authorized routers by
illegitimately assumes a legitimate router's identity. All types of
attackers (compromised links, compromised routers unauthorized
routers, and masquerading routers) can spoof. When an attacker
succeeds to spoof, it plays a role of masquerading router.
The consequences of spoofing are:
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o The disclosure of routing information: The masquerading router
will be able to participate in the routing computation and
exchanges, and consequently gain access to the routing
information.
o The deception of peer relationship: The authorized routers, which
exchange routing messages with the masquerading router, do not
realize they are peering with a router that is faking another
router's identity.
Spoofing is special in that it can be used to carry out other threat
actions causing other threat consequences. For example, after an
attacker spoofs successfully, it can send out unrealistic routing
information that might cause disruption of network services. Please
note these consequences are directly resulted from other threat
actions instead of spoofing, which are also discussed in this
documentation. It can be said that spoofing is the means by which one
masquerades.
The threat consequence zone covers two different scopes:
The consequence zone of the disclosed routing information depends
on what routing information has been exchanged between the
attacker and its peers.
The disclosure of routing information: The masquerading router
will participate in the routing computation and exchanges, and
consequently gain access to the routing information.
There are other consequences caused by a spoofing (masquerading)
router. For example, the masquerading router might cause disruption
of a network by sending unrealistic routing information. But these
consequences are directly resulted from other threat actions instead
of spoof.
The threat consequence zone covers two different scopes:
o The consequence zone of the fake peer relationship will be limited
to those routers mistrusting the attacker's identity.
o The consequence zone of the disclosed routing information depends
on the attacker's location, the routing protocol type, and,
ultimately, what routing information has been exchanged between
the attacker and its deceived peers.
The threat consequence period has two different definitions too:
o The consequence period of the fake peer relationship is same as
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the duration of the spoof. As soon as the attacker stops spoofing,
the fake peer relationship disappears.
o The consequence period of the disclosed routing information will
be longer than the duration of the spoof. After the attacker stops
spoofing, its knowledge will not be out-dated until there is a
topology change of the disclosed network.
4.5 Falsification
Falsification is defined as an intentional action whereby false
routing information is being sent. Routers use routing information
to depict network topology, compute routing table, and further
forward data traffic. False routing information describes the network
in an unrealistic view, whether or not intended by the authoritative
network administrator.
To falsify the routing information, an attacker has to be either the
originator or a forwarder of the routing information. It cannot be a
receiver-only.
4.5.1 Falsifications by Originators
An originator of routing information can launch following
falsifications:
4.5.1.1 Overclaiming
An over-claiming is defined as an action that an attacker employs to
advertise its ownership of some network resources, while in reality,
this ownership does not exist, or the advertisement is not
authorized. This is given in Figure 2 and Figure 3 below.
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+-------------+ +-------+ +-------+
| Internet |---| Rtr B |---| Rtr A |
+------+------+ +-------+ +---+---+
| |
| |
| |
| *-+-*
+---+---+ / \
| Rtr C |------------------* N 1 *
+-------+ \ /
*---*
Figure 2
+-------------+ +-------+ +-------+
| Internet |---| Rtr B |---| Rtr A |
+------+------+ +-------+ +-------+
|
|
|
| *---*
+---+---+ / \
| Rtr C |------------------* N 1 *
+-------+ \ /
*---*
Figure 3
The above figures provide examples. Router A, the attacker, is
connected with the Internet through Router B. Router C is authorized
to advertise its link to Network 1. In Figure 2, Router A owns a
link to the Network 1, but is not authorized to advertise it. In
Figure 3, Router A does not own such a link. But in either case,
Router A advertises the link to the Internet, through Router B.
Compromised routers, unauthorized routers, and masquerading routers
can over-claim network resources.
The consequence of overclaiming includes:
o Usurpation of the overclaimed network resources. In Figure 2
and 3, it will cause a usurpation of Network 1 when Router B or
other routers on the Internet (not shown in the figures) believe
that Router A provides the best path to reach the Network 1. They,
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the routers, thereby forward the data traffic, destined to Network
1, to Router A. The best result is the data traffic uses an
unauthorized path (Figure 2), and the worst case is the data
never reach the destination Network 1 (Figure 3). The ultimate
consequence is Router A gains the control over the Network 1's
services, by controlling the data traffic.
o Usurpation of the legitimate advertising routers. In Figure 2
and 3, Router C is the legitimate advertiser of Network 1. By
overclaiming, Router A also controls (partially or totally) the
services/functions provided by the Router C. (This is NOT a
disruption, because Router C is operating in a way intended by the
authoritative network administrator.)
o Deception of other routers. In Figure 2 and 3, Router B, or
other routers on the Internet, might be deceived to believe the
path through Router A is the best.
o Disruption of data planes on some routers. This might happen on
routers that are on the path, which is used by other routers to
reach the overclaimed network resources through the attacker. In
Figure 2 and 3, when other routers on the Internet are
deceived, they will forward the data traffic to Router B, which
might be overloaded.
The threat consequence zone varies based on the consequence:
o Where usurpation is concerned, the consequence zone covers the
network resources that are overclaimed by the attacker (Network 1
in Figure 2 and 3), and the routers that are authorized to
advertise the network resources but lose the competition against
the attacker(Router C in Figure 2 and 3).
o Where deception is concerned, the consequence zone covers the
routers that do not believe the attacker's advertisement and use
the attacker to reach the claimed subnets (Router B and other
deceived routers on the Internet in Figure 2 and 3).
o Where disruption is concerned, the consequence zone includes the
routers that are on the path of misdirected data traffic (Router B
in Figure 2 and 3).
The threat consequence will cease when the attacker stops
overclaiming, and will totally disappear when the routing tables are
converged. As a result the consequence period is longer than the
duration of the overclaiming.
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4.5.1.2 Underclaiming
An underclaiming threat is defined as an action that an attacker
illegitimately hides its authorized ownership of some network
resources. The attacker could be the only router authorized to claim
the network resources, or there might exist some legitimate backup
routers. Figures below provide two examples.
+-------------+ +-------+
| Internet |---| Rtr A |
+------+------+ +---+---+
| |
| |
| |
| *-+-*
+---+---+ / \
| Rtr B | * N 1 *
+-------+ \ /
*---*
Figure 4
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+-------------+ +-------+
| Internet |----------------| Rtr A |
+------+------+ +---+---+
| |
| |
| |
| *-+-*
+---+---+ +-------+ / \
| Rtr C |-----| Rtr B |-----* N 1 *
+-------+ +-------+ \ /
*---*
Figure 5
Router A, the attacker, owns a link to Network 1 and is authorized to
advertise Network 1. Nevertheless, Router A refuses to advertise
Network 1. In Figure 4, Network 1 is single-homed with Router A and
therefore can only be advertised by Router A. In Figure 5 Network is
dual-homed with Router A and B, and both routers are authorized to
advertise Network 1 (Router A may or may not provide a preferred path
against Router B, the backup router).
Compromised routers, unauthorized routers, and masquerading routers
can underclaim network resources.
The consequence of underclaiming includes:
o Usurpation of the underclaimed network resources: In Figure 5 when
Router A underclaims Network 1, Network 1 is isolated from the
rest of the world, and cannot provide services to other devices,
though Network 1's own operation is not disrupted. In Figure 4,
if the path through Router A is preferred, the underclaiming will
force Network 1 to use a sub-optimal path to provide its services.
(If the path through Router B is intended to be preferred, the
services by Network 1 will not really be hurt even though Router A
underclaims).
o Usurpation of the legitimate backup routers. In Figure 5, Router
A's path is preferred but Router A underclaims Network 1, it
actually force Router B to serve Network 1. (Again, if Router B's
path is intended to be preferred, Router A's underclaim does not
really usurp Router B.)
o Deception of other routers. Routers on the Internet (not shown in
Figure 4 or Figure 5) might not be able to reach Network 1 (Figure
5) or have to use a sub-optimal path through Router B when
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Router A's path is preferred.
o Disruption of data planes on some routers. This might happen on
routers that are on the sub-optimal paths. In Figure 5, when
other routers on the Internet are deceived and use the sub-optimal
path through Router B to reach Network 1, they will forward the
data traffic to Router C. Router B and C might then become
overloaded. (When the path through Router B is intended to be
preferred, Router B and C might also be overloaded. However, the
disruption in such a case is not a consequence of an underclaim).
Note: Some others type of usurpation might result from an underclaim
in routing protocols. Below Figure provides an example.
*---* *---*
/ \ +-------+ +-------------+ +-------+ / \
* N 2 *---| Rtr B |---| Internet |---| Rtr A |---* N 1 *
\ / +-------+ +-------------+ +-------+ \ /
*---* *---*
Figure 6
In Figure 6, Network 2 is attached with the Router B and provides
similar services as Network 1. When Router A hides Network 1, devices
on the Internet will turn to Network 2 for those services. Although
this issue results from an underclaim in routing protocol, this is
rather a usurpation issue in related service (application) protocols,
and we are not discussing it in detail in this documentation.
The threat consequence zone varies based on the consequence:
o Where usurpation is concerned, the consequence zone covers the
network resources that are underclaimed by the attacker (Network 1
in Figure 4 and 5), and the routers that are intended to be
backup with a lower preference (Router B in Figure 5, if Router
A's path is preferred).
o Where deception is concerned, the consequence zone covers the
routers that cannot reach the underclaimed network resources or
those that have to use sub-optimal paths.
o Where disruption is concerned, the consequence zone covers the
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routers that cannot reach the underclaimed network resources or
those that have to use sub-optimal paths.
Like overclaiming, the consequence period is longer than the duration
of the underclaiming--the threat consequence will mitigate when the
attacker stops underclaiming and will totally disappear when routing
tables are converged.
4.5.1.3 Misclaiming
A Misclaiming threat is defined as an attacker action advertising its
authorized ownership of some network resources in a way that is not
intended by the authoritative network administrator. An attacker can
eulogize or disparage when advertising these network resources.
Compromised routers, unauthorized routers, and masquerading routers
can misclaim network resources.
The threat consequences of Misclaiming are a combination of
consequences from overclaiming and underclaiming. Eulogizing the
network resources might cause the same consequences made by
overclaiming, while disparaging might trigger the same results from
underclaiming.
The consequence zone and period are also similar to those of
overclaiming or underclaiming.
4.5.2 Falsifications by Forwarders
When a legitimate router forwards routing information, it must or
must not modify the routing information, depending on the routing
information and the routing protocol type. For example, in RIP, the
forwarder must modify the routing information by increasing the hop
count by 1. On the other hand, the forwarder must not modify the type
1 LSA in OSPF. In general, forwarders in distance vector routing
protocols are authorized to and must modify the routing information,
while most forwarders in link state routing protocols are not
authorized to and must not modify most routing information.
As a forwarder authorized to modify routing message, an attacker does
not forward necessary routing information to other authorized
routers. Unauthorized aggregation (summarization) is special type of
understatements.
4.5.2.1 Misstatement
This is defined as an action whereby the attacker describes route
attributes in a wrong way. For example, in RIP, the attacker
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increases the path cost by two hops instead of one. Another example
is, in BGP, the attacker deletes some AS numbers from the AS PATH.
When forwarding routing information that should not be modified, an
attacker can launch the following falsifications:
o Deletion: Attacker deletes valid data in the routing message.
o Insertion: Attacker inserts false data in the routing message.
o Substitution: Attacker replaces valid data in the routing message
with false data.
o Replaying: Attacker replays out-dated data in the routing message.
All types of attackers (Compromised links, compromised routers,
unauthorized routers, and masquerading routers) can falsify the
routing information when they forward the routing messages.
The threat consequences of these falsifications by forwarders are
similar to those caused by originators: Usurpation of some network
resources and related routers; deception of routers using false
paths; and disruption of data planes of routers on the false paths.
The threat consequence area and period are also similar.
4.6 Interference
Interference is defined as a threat action where attackers inhibit
exchanges on legitimate routers. Attackers can do this by adding
noise, not forwarding packets, replaying out-dated packets, delaying
responses, denial of receipts, and breaking synchronization.
Compromised links can interfere with the routing exchanges over the
links where they have control. Compromised, unauthorized and
masquerading routers can slowdown their routing exchanges or create
flapping routing sessions of the legitimate peering routers.
The consequence of interference is the disruption of routing
operations.
The consequence zone of interference varies based on the source of
the threats:
o When a compromised link launches the action, the threat
consequence zone covers routers that are using the link to
exchange the routing information. Routers behind might be
disrupted too.
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o When compromised routers, unauthorized routers, or masquerading
routers are the attackers, the threat consequence zone covers
routers with which the attackers are exchanging routing
information, and router behind.
o The threat consequences might disappear as soon as the
interference is stopped, or might not totally disappear until the
networks are converged. Therefore, the consequence period is
equal or longer than the duration of the interference.
4.7 Overload
Overload is defined as a threat action whereby attackers place excess
burden on legitimate routers. Attackers can overload data plane or
control plane. Because data plane is involved in routing exchanges,
overload of data plane will also influence the routing operations.
The consequence of overload is the disruption of routing operations.
The consequence zone varies based on several factors:
o When compromised links launch an overload action against the
control plane, the consequence zone covers routers that are using
the links to exchange the routing information, and routers behind.
o When compromised links launch an overload action against the data
plane, the consequence zone coves routers that are physically
connected by the links, and routers behind.
o When Compromised routers, unauthorized routers, or masquerading
routers launch an overload action against the control plane, the
threat consequence zone covers routers with which the attackers
are exchanging routing, and routers behind.
o When Compromised routers, unauthorized routers, or masquerading
routers launch an overload action against the data plane, the
threat consequence zone covers of routers with which the attackers
have physical connections, and routers behind.
The threat consequences might disappear as soon as the overload is
stopped, or not disappear until networks are converged.
4.8 Byzantine Failures
When a host or network behaves in a way contrary to the protocol
specification or in a way that is not authorized, the behavior is
called a "Byzantine failure"[BYZANTINE].These failures can include
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timing error (producing messages at intervals contrary to the
specification), protocol errors (producing messages at variance with
the specification, e.g., responding with the incorrect message type),
or data error (producing messages that carry faulty data).
Byzantine attacks may be seen where any intermediate node or group of
nodes can intentionally create routing loops, misrouting packets on
non-optimal paths, or selectively dropping packets (black hole).
Another way to state the problem is that Byzantine failures occur
when a processor returns incorrect or malicious data. Under such an
attack, only the source and destination nodes are assumed to be
trusted. Detecting a Byzantine error is harder than the fail-stop
model in the sense that at least one other processor must do the same
computation to confirm the results. What isn't clear is just how
much validation is required to determine whether a Byzantine failure
has occurred
4.9 Discarding of Control Packets
Similar to Byzantine threats discussed above, uncontrolled discarding
of control packets lies in the same plane. That is, discarding of
control packets will have the same consequence as an incorrect
routing control packet propagated in the network by a compromised
router. In distance vector protocols the consequences may not be as
dire because of the protocol behavior, i.e. the routing update, is
exchanged only with the neighbor. However in the case of link state
routing protocols, the threat associated to discarding of control
packet can become a serious issue, as the routing updates are flooded
in the network. Exploitation of this threat was discussed by S.F. Wu
B. Vetter and F. Wang from the perspective of an insider attacks in
a Link State Routing environment. It is worth considering this
threat in more detail.
If the compromised (bad) router partitions the network, i.e. the
router is the only path between two good routers, then the bad router
can avoid forwarding the routing information on to the network on the
other side.
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*-----* *-----*
/ \ *---* / \
/ Routers \ / \ / Routers \
* on one *------* F *-------* on other *
\ side / \ / \ side /
\ / *---* \ /
*-----* *-----*
Figure 7
In this scenario, the network is partitioned and either side may not
receive correct updates and the update packets may be dropped.
Clearly if F is positioned such that the network is not partitioned,
then the correctness of the protocol in such circumstances depends on
the mechanism of transmitting routing updates. In the case of a
typical LSRP like OSPF, reliable flooding is used that guarantees
that the updates are received by each and every router in the
network. Hence even when a set of bad routers partition a network, if
there exists at least one good path between all the routers then this
threat can be deterred by designing a robust transmitting mechanism
for control updates.
4.10 Network Mapping Threats
Based on a simple set of inputs, computers can generate graphical and
quantitative representations of informal knowledge networks within an
organization. If there were no preventive measures in place, network
map knowledge obtained by unauthorized access to intelligence can be
costly and expensive threats. Motivation for snooping can range from
curiosity to voyeur tendencies. The threat with router plane data
snooping is the fact that it looks to historical information to be an
indication of what will happen in the future. The principal threat
aspect is that the snooped data can be used to develop a network
topology. When unauthorized attackers develop a model, they attempt
to create one that will be relevant for all situations going forward.
Although these models may not be exact for every situation, they can
be applied with a reasonable amount of certainty without introducing
any biases based on past information.
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5. Multicast Routing Protocol Considerations
Based on a simple set of inputs, computers can generate graphical and
quantitative representations of informal knowledge networks within an
organization. If there were no preventive measures in place, network
map knowledge obtained by unauthorized access to intelligence can be
costly and expensive threats. Motivation for snooping can range from
curiosity to voyeur tendencies. The threat with router plane data
snooping is the fact that it looks to historical information to be an
indication of what will happen in the future. The principal threat
aspect is that the snooped data can be used to develop a network
topology. When unauthorized attackers develop a model, they attempt
to create one that will be relevant for all situations going forward.
Although these models may not be exact for every situation, they can
be applied with a reasonable amount of certainty without introducing
any biases based on past information.
In general, multicast routing updates can be fabricated, modified,
replayed, deleted, and snooped. For example, unauthorized nodes can
simply participate in the multicast routing protocol dialog when no
access control mechanisms are defined for the protocol. Non-routing
devices can masquerade as an authorized router and inject spurious
routing updates, perhaps using source routing attacks or TCP session
hijacking attacks. Communication links can be compromised by an
intruder to facilitate the manipulation of routing messages.
Individual routers can be attacked and compromised to run modified
software, or use a modified configuration.
Multicast communication may be specifically targeted by security
threats, due to its potential for communicating with large numbers of
receivers simultaneously. An attacker may attempt to use multicast
sessions in order to spread specific data to recipients, or may use
multicast traffic patterns to overload links as a denial-of-service
(DOS) attack.
In some architecture such as PIM-DM, even routers which are not
actively participating in the multicast tree must maintain state
information on active groups within the routing domain.
Multicast routing protocols are at least as susceptible as unicast
routing protocols to security threats. In general, multicast routing
updates can be fabricated, modified, replayed, deleted, and snooped.
For example, unauthorized nodes can simply participate in the
multicast routing protocol dialog when no access control mechanisms
are defined for the protocol. Non-routing devices can masquerade as
an authorized router and inject spurious routing updates, perhaps
using source routing attacks or TCP session hijacking attacks.
Communication links can be compromised by an intruder to facilitate
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the manipulation of routing messages. Individual routers can be
attacked and compromised to run modified software, or use a modified
configuration.
Just as with unicast routing, the key vulnerabilities of multicast
routing lie in the introduction of misleading routing information,
through non-existent (black hole) or incorrect routes, or in
intercepting the routing information for malicious purposes.
Incorrect routing information can form the basis for DOS attacks,
while intercepting routing information (particularly group membership
information) can reveal compromising topological information.
Denial-of-service attacks may come either from senders or receivers
in the multicast model. That is, if uncontrolled, senders may create
large numbers of multicast groups, thus potentially creating a
processing burden on multicast routers throughout the domain.
Receivers, if uncontrolled, may join large numbers of multicast
groups, thus causing the establishment of paths from the senders in
each group to the receiver, as well as causing the flow of packets
for each of the groups to converge on the receiver.
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6. Security Considerations
This entire informational draft RFC is security related. Specifically
it addresses security of routing protocols as associated with threats
to those protocols. In a larger context, this work builds upon the
recognition of the IETF community that signaling and control/
management planes of networked devices need strengthening. Routing
protocols can be considered part of that signaling and control plane.
However, to date, routing protocols have largely remained unprotected
and open to malicious attacks. This document discusses inter and
intra domain routing protocol threats as we know them today and lays
the foundation for a future draft which fully discusses security
requirements for routing protocols.
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References
[SEC-GLOSS] R.Shirey, Internet Security Glossary, RFC 2828, May 2000
[DV-SECURITY] B.R.Smith, S.Murthy, and J.J. Garcia-Luna-Aceves,
Securing Distance-Vector Routing Protocols, Symposium on Network and
Distributed System Security 1997, Feb. 1997
[PROTO-VULN] E.Rosen, Vulnerabilities of Network Control Protocols: An
Example, Computer Communication Review, Jul. 1981
[BYZANTINE] R.Perlman, Network Layer Protocols with Byzantine Robustness,
August 1988
[OSPF-SIG] S. Murphy, M. Badger, and B. Wellington, OSPF with
Digital Signatures, RFC2154, June 1997
[OSPFv2] J.Moy, OSPF Version 2, RFC 2328, April 1998
[SENSOR-IDS] V.Mittal and G.Vigna, Sensor-Based Intrusion Detection for
Intra-Domain Distance-Vector Routing, Proceedings of the ACM Conference
on Computer and Communication Security (CCS'02), Washington, DC,
November 2002
[DOS-IDS] S.Cheung et. al., Protecting Routing Infrastructures from
Denial of Service using co-operative intrusion detection, In Proceedings
of the 1995 IEEE Symposium on Security and Privacy
[DIST-MONINTOR] K.A. Bradley et. al., A distributed Network Monitoring
approach
[ATTACK-LS] S.F. Wu B. Vetter, and F. Wang.An Experimental Study of
Insider Attacks in a Link State Routing Protocol, In 5th IEEE
International Conference on Network Protocols, Atlanta, GA, 1997.
[IGMP] B. Cain, S. Deering, I. Kouvelas, B. Fenner, and A. Thyagarajan,
Internet Group Management Protocol, Version 2, RFC 3376, October 2002
[PIM-SM] D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S. Deering,
M. Handley, V. Jacobson, C. Liu, P. Sharma, and L. Wei, Protocol
Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification,
RFC 2362, June 1998
[THREATS] - A. Ballardie and J. Crowcroft, Multicast-Specific Security
Threats and Counter-Measures;; In Proceedings "Symposium on Network and
Distributed System Security", February 1995, pp.2-16.
(ftp://cs.ucl.ac.uk/darpa/IDMR/mcast-sec-isoc.ps.Z)
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Authors' Addresses
Dennis Beard
Nortel Networks
3500 Carling Avenue
Nepean, Ontario K2H 8E9
Canada
Phone:
EMail: beardd@nortelnetworks.com
Sandy Murphy
Network Associates, Inc
3060 Washington Rd.
Glenwood, MD 21738
USA
Phone: 443-259-2303
EMail: Sandra_murphy@nai.com
Yi Yang
Cisco Systems
7025 Kit Creek Road
RTP, NC 27709
USA
Phone:
EMail: yiya@cisco.com
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Appendix A. Acknowledgements
This draft would not have been possible save for the excellent efforts
and team work characteristics of those listed here.
Ayman Musharbash - Nortel Networks
Paul Knight - Nortel Networks
Elwyn Davies - Nortel Networks
Ameya Dilip Pandit - Graduate student - University of Missouri
Senthilkumar Ayyasamy - Graduate student - University of Missouri
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Intellectual Property Statement
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Acronyms
AODV - Ad-hoc On-demand Distance Vector routing protocol
AS - Autonomous system. Set of routers under a single technical
administration. Each AS normally uses a single interior gateway
protocol (IGP) and metrics to propagate routing information
within the set of routers. Also called routing domain.
AS-Path - In BGP, the route to a destination. The path consists
of the AS numbers of all routers a packet must go through to reach a
destination.
BGP - Border Gateway Protocol. Exterior gateway protocol used to
exchange routing information among routers in different autonomous
systems.
eBGP - External BGP. BGP configuration in which sessions are
established between routers in different ASs.
iBGP - Internal BGP. BGP configuration in which sessions are
established between routers in the same ASs.
LSRP - Link-State Routing Protocol
LSA - Link-State Announcement
M-OSPF - Multicast Open Shortest Path First
NLRI - Network layer reachability information. Information that
is carried in BGP packets and is used by MBGP.
OSPF - Open Shortest Path First. A link-state IGP that makes
routing decisions based on the shortest-path-first (SPF) algorithm
(also referred to as the Dijkstra algorithm).
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PIM (and PIM DM) - Protocol Independent Multicast. A
protocol-independent multicast routing protocol. PIM Sparse Mode
routes to multicast groups that might span wide-area and
interdomain internets. PIM Dense Mode is a flood-and-prune protocol.
RIP - Routing Information Protocol. Distance-vector interior
gateway protocol that makes routing decisions based on hop count.
SPF - Shortest-path first, an algorithm used by IS-IS and OSPF
to make routing decisions based on the state of network links. Also
called the Dijkstra algorithm.
TCP - Transmission Control Protocol. Works in conjunction with
Internet Protocol (IP) to send data over the Internet. Divides a
message into packets and tracks the packets from point of origin
to destination.
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