ECRIT H. Tschofenig
Internet-Draft Siemens
Expires: August 18, 2006 H. Schulzrinne
Columbia U.
M. Shanmugam
Siemens
T. Taylor
Nortel
February 14, 2006
Security Threats and Requirements for Emergency Call Mapping
draft-taylor-ecrit-security-threats-02.txt
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Abstract
This document reviews the security threats to the process of mapping
locations to URIs pointing to Public Safety Answering Points (PSAPs).
This mapping occurs as part of the process of routing emergency calls
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through the IP network. Based on the threats, this document
establishes a set of security requirements for the mapping protocol,
which is being developed by the ECRIT Working Group.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Mapping and the emergency call routing process . . . . . . . . 5
4. Motivations of attackers . . . . . . . . . . . . . . . . . . . 6
5. Potential attacks . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Attacks to prevent a specific individual from
receiving aid . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Attacks to gain information about an emergency . . . . . . 7
5.3. Attacks to gain fraudulent use of ASP/VSP services . . . . 8
5.4. Attacks against the emergency response system . . . . . . 9
6. Security requirements relating to emergency call routing . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Introduction
Legacy telephone network (PSTN) users can summon help for emergency
services such as ambulance, fire and police using a well known unique
number (e.g., 911 in North America, 112 in Europe). A key factor in
the handling of such calls is the ability of the system to determine
caller location and to route the call to the appropriate Public
Safety Answering Point (PSAP) based on that location. With the
introduction of IP-based telephony and multimedia services, support
for emergency calling via the Internet also has to be provided. As
one of the steps to achieve this, a protocol must be developed
allowing a client entity to submit a location and receive a URI
pointing to the applicable PSAP for that location.
Attacks against the PSTN (many focussing on free calling) have taken
place for decades. The Internet is seen as an even more hostile
environment. Thus it is important to understand the types of attacks
that might be mounted against the infrastructure providing emergency
services, and to develop security mechanisms to counter those
attacks. In view of the mandate of the ECRIT Working Group, the
present document restricts itself to attacks on the mapping of
locations to PSAP URIs.
This document is organized as follows: Section 2 describes basic
terminology. Section 3 briefly describes how mapping fits within the
process of routing emergency calls. Section 4 describes some
motivations of attackers in the context of ECRIT, Section 5 describes
and illustrates the attacks that might be used, and Section 6 lists
the security-related requirements that must be met if these attacks
are to be mitigated.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119], with the
qualification that unless otherwise stated they apply to the design
of the mapping protocol, not its implementation or application.
Application (Voice) Service Provider (ASP/VSP), mapping service,
emergency address, emergency caller, emergency identifier, mapping,
mapping client, mapping server, mapping protocol, and Public Safety
Answering Point (PSAP) are taken from [I-D.ecrit-requirements].
Location information is taken from RFC 3693 [RFC3693].
The term "emergency caller's device" designates the IP host closest
to the emergency caller in the signalling path between the emergency
caller and the PSAP. Examples include an IP phone running SIP,
H.323, or a proprietary signalling protocol, a PC running a soft
client, or an analogue terminal adapter or a residential gateway
controlled by a softswitch.
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3. Mapping and the emergency call routing process
The first goal of emergency call routing is to ensure that any
emergency call is routed to a PSAP. Preferably the call is routed to
the PSAP responsible for the caller's location, since misrouting
consumes valuable time while the call taker locates and forwards the
call to the right PSAP. As described in [I-D.ecrit-requirements],
mapping is part of the process of achieving this preferable outcome.
In brief, mapping involves a mapping client, a mapping server, and
the protocol that passes between them. The protocol allows the
client to pass location information to the mapping server and receive
back a URI which can be used to direct call signalling to a PSAP.
Since mapping requires location information for input, when and where
the location information is acquired constrains when mapping can be
done and which devices can act as mapping clients. The key
distinction in "when" is before the emergency or during the
emergency. The key distinction in "where" is at the emergency
caller's device or at another device in the signalling path between
the emergency caller and the PSAP. The device that acquires the
location information can be the mapping client, and so can any device
downstream of that point. It is even possible for a PSAP itself to
initiate mapping, to determine whether an arriving call should be
handled by a call taker at that PSAP or should be proxied to another
PSAP.
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4. Motivations of attackers
Attackers may direct their efforts either against an individual or
against a portion of the emergency response system. Attacks against
an individual fall into three classes:
o attacks to prevent an individual from receiving aid;
o attacks to gain information about an emergency that can be applied
either against an individual involved in that emergency or to the
profit of the attacker;
o attacks by the caller to gain fraudulent use of ASP/VSP services,
by using an Emergency Identifier to bypass normal authentication,
authorization, and accounting procedures.
Attacks against the emergency response system are aimed either at
denying system services to all users in a given area, or at diverting
emergency responders to non-emergency sites. The latter motivation
falls outside the scope of this analysis. One interesting variant on
the "system denial" motivation is the case where a victim of a large
emergency hopes to gain faster service by blocking others' competing
calls for help.
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5. Potential attacks
This section describes classes of attacks on the mapping process that
could be used to achieve the attacker goals described in the previous
section.
5.1. Attacks to prevent a specific individual from receiving aid
This section discusses blocking attacks directed at a specific
individual. The more general blocking attacks described in
Section 5.4 will also operate to the same effect. They are discussed
separately because the separation may be useful when weighing the
priority for implementing specific defenses.
Blocking attacks against an individual can operate against the
operation of the mapping protocol, or through impersonation of the
mapping server. It is also possible that the mapping protocol is
used indirectly to interfere with other aspects of the emergency call
process.
The basic attacks available against protocol operation are denial of
service, interference through message insertion, and interference
through man-in-the middle alteration of messages. Denial of service
can be achieved in several ways: by flooding attacks on the client or
server, by taking control of the mapping client, by installing
filters on the channel, or by installing filters at the mapping
server. Man-in-the-middle attacks also involve taking control of the
channel or the mapping server.
The attacks based on control of the mapping server can also be
carried out using impersonation of the mapping server. This may be
an easier attack to execute in some circumstances.
The mapping protocol may also be used to support a reflection attack
on the mapping client or on some other component of the routing
chain. To execute this attack, the attacker impersonates the target
when sending requests to the mapping server.
5.2. Attacks to gain information about an emergency
This section discusses attacks used to gain information about an
emergency. The attacker may be seeking the location of the caller
(e.g., to effect a criminal attack). The attacker may be seeking
information that could be used to link an individual (the caller or
someone else involved in the emergency) with embarrassing information
related to the emergency (e.g., "Who did the police take away just
now?"). Finally, the attacker could be seeking to profit from the
emergency, perhaps by offering his or her services (e.g., news
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reporter, "ambulance chaser").
The primary information that interceptions of mapping requests and
responses will reveal are a location, a URI identifying a PSAP, and
the addresses of the mapping client and server. The location
information can be directly useful to an attacker if the attacker has
high assurance that the observed query is related to an emergency
involving the target. The other pieces of information may provide
the basis for further attacks on emergency call routing, but because
of the time factor, are unlikely to be applicable to the routing of
the current call. However, if the mapping client is the emergency
caller's device, the attacker may gain information that allows for
interference with the call after it has been set up or interception
of the media stream between the caller and the PSAP.
5.3. Attacks to gain fraudulent use of ASP/VSP services
This section discusses attacks whereby the Emergency Caller is hoping
to bypass normal procedures to achieve free use of ASP/VSP services.
An attack of this sort is possible only if the following conditions
are true:
a. The attacker is the emergency caller.
b. The attacker has control over the addressing of the emergency
call request either as a result of or subsequent to the mapping
operation.
c. The call enters the domain of an ASP/VSP, which accepts it
without applying normal requirements for an authenticated
subscriber identity because it is marked as an emergency call.
d. The ASP/VSP routes it according to the called address (e.g., SIP
Request-URI), without verifying that this is the address of a
PSAP.
The key condition is the second one. The attacker has two
possibilities for controlling the addressing of the call. One is to
insert a false entry into the mapping database for the caller's
location, allowing the caller free calls to wherever the entry points
to. The second possibility comes if the emergency caller's device is
the mapping client. In this case, if the caller reprograms the
device to accept an arbitrary input in place of the URI returned by
the mapping process, the caller is able to complete a call to that
URI while bypassing the ASP/VSP's normal authentication procedures.
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5.4. Attacks against the emergency response system
This section considers attacks intended to reduce the effectiveness
of the emergency response system for all callers in a given area.
The motivation may range from thoughtless vandalism, to wide-scale
criminality, to terrorism.
The possible attacks on the mapping process to achieve this have
already been described; they simply have to be less targeted. The
attacks are denial of service or misdirection through provision of
incorrect responses to mapping queries. The mechanisms are flooding
attacks (for denial of service only), control of the Mapping Server,
or impersonation of the Mapping Server.
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6. Security requirements relating to emergency call routing
This section describes the security requirements which must be
fulfilled in the mapping protocol to prevent or blunt the
effectiveness of the attacks described in the previous section.
Attack: flooding attack on the mapping client, mapping server, or a
third entity.
Requirement: The mapping protocol MUST NOT create new opportunities
for flooding attacks, including amplification attacks.
Attack: insertion of interfering messages.
Requirement: The protocol MUST permit the mapping client to verify
that the response is a response to the query it sent out.
Attack: man-in-the-middle alteration of messages.
Requirement: The protocol MUST permit the application of the
integrity service to requests and responses as an implementation
option.
Attack: impersonation of the mapping server.
Requirement: the protocol MUST permit the mapping client to
authenticate the mapping server as an implementation option.
Attack: snooping of location and other information.
Requirement: the protocol MUST permit the use of the confidentiality
service as an implementation option.
Attack: fraudulent calls.
Requirement: the protocol MUST permit the reverse lookup of URIs to
verify that a URI corresponds to a PSAP in the mapping database.
Note - the necessity to use this capability depends on whether the
system architecture satisfies the conditions listed in
Section 5.3. If the emergency caller's device is not the mapping
client, the opportunity for fraud is very much limited.
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7. Security Considerations
This document addresses security threats and security requirements.
Therefore, security is considered throughout this document.
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8. Acknowledgements
Hannes Tschofenig performed the initial security analysis for ECRIT.
The authors would like to thank Stephen Kent for his extensive
comments on previous issues of this document, which led to a complete
rewriting of it.
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9. IANA Considerations
This document does not require actions by the IANA.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[I-D.ecrit-requirements]
Schulzrinne, H. and R. Marshall, "Requirements for
Emergency Context Resolution with Internet Technologies",
February 2006.
[RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
J. Polk, "Geopriv Requirements", RFC 3693, February 2004.
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Authors' Addresses
Hannes Tschofenig
Siemens
Otto-Hahn-Ring 6
Munich, Bayern 81739
Germany
Email: Hannes.Tschofenig@siemens.com
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
USA
Phone: +1 212 939 7042
Email: schulzrinne@cs.columbia.edu
URI: http://www.cs.columbia.edu/~hgs
Murugaraj Shanmugam
Siemens
Otto-Hahn-Ring 6
Munich, Bayern 81739
Germany
Email: murugaraj.shanmugam@siemens.com
Tom Taylor
Nortel
1852 Lorraine Ave
Ottawa, Ontario K1H 6Z8
Canada
Email: taylor@nortel.com
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