draft-ietf-stir-threats-00.txt   draft-ietf-stir-threats-01.txt 
Network Working Group J. Peterson Network Working Group J. Peterson
Internet-Draft NeuStar, Inc. Internet-Draft NeuStar, Inc.
Intended status: Informational October 12, 2013 Intended status: Informational February 5, 2014
Expires: April 15, 2014 Expires: August 9, 2014
Secure Telephone Identity Threat Model Secure Telephone Identity Threat Model
draft-ietf-stir-threats-00.txt draft-ietf-stir-threats-01.txt
Abstract Abstract
As the Internet and the telephone network have become increasingly As the Internet and the telephone network have become increasingly
interconnected and interdependent, attackers can impersonate or interconnected and interdependent, attackers can impersonate or
obscure calling party numbers when orchestrating bulk commercial obscure calling party numbers when orchestrating bulk commercial
calling schemes, hacking voicemail boxes or even circumventing multi- calling schemes, hacking voicemail boxes or even circumventing multi-
factor authentication systems trusted by banks. This document factor authentication systems trusted by banks. This document
analyzes threats in the resulting system, enumerating actors, analyzes threats in the resulting system, enumerating actors,
reviewing the capabilities available to and used by attackers, and reviewing the capabilities available to and used by attackers, and
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 15, 2014. This Internet-Draft will expire on August 9, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction and Scope . . . . . . . . . . . . . . . . . . . 2 1. Introduction and Scope . . . . . . . . . . . . . . . . . . . 2
2. Actors . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Actors . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Intermediaries . . . . . . . . . . . . . . . . . . . . . 4 2.2. Intermediaries . . . . . . . . . . . . . . . . . . . . . 4
2.3. Attackers . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Attackers . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Voicemail Hacking via Impersonation . . . . . . . . . . . 6 3.1. Voicemail Hacking via Impersonation . . . . . . . . . . . 6
3.2. Unsolicited Commercial Calling from Impersonated Numbers 7 3.2. Unsolicited Commercial Calling from Impersonated Numbers 7
4. Attack Scenarios . . . . . . . . . . . . . . . . . . . . . . 8 3.3. Telephony Denial-of-Service Attacks . . . . . . . . . . . 8
4.1. TBD: Solution-Specific Attacks . . . . . . . . . . . . . 8 4. Attack Scenarios . . . . . . . . . . . . . . . . . . . . . . 9
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. Solution-Specific Attacks . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Informative References . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Informative References . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction and Scope 1. Introduction and Scope
As is discussed in the STIR problem statement [9], the primary As is discussed in the STIR problem statement [2], the primary
enabler of robocalling, vishing, swatting and related attacks is the enabler of robocalling, vishing, swatting and related attacks is the
capability to impersonate a calling party number. The starkest capability to impersonate a calling party number. The starkest
example of these attacks are cases where automated callees on the example of these attacks are cases where automated callees on the
PSTN rely on the calling number as a security measure, for example to PSTN rely on the calling number as a security measure, for example to
access a voicemail system. Robocallers use impersonation as a means access a voicemail system. Robocallers use impersonation as a means
of obscuring identity; while robocallers can, in the ordinary PSTN, of obscuring identity; while robocallers can, in the ordinary PSTN,
block (that is, withhold) their caller identity, callees are less block (that is, withhold) their caller identity, callees are less
likely to pick up calls from blocked identities, and therefore likely to pick up calls from blocked identities, and therefore
calling from some number, any number, is preferable. Robocallers calling from some number, any number, is preferable. Robocallers
however prefer not to call from a number that can trace back to the however prefer not to call from a number that can trace back to the
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scope of impersonation considered in this model. Furthermore, scope of impersonation considered in this model. Furthermore,
impersonating a reached number to the originator of a call is outside impersonating a reached number to the originator of a call is outside
the scope of this threat model. the scope of this threat model.
In much of the PSTN, there exists a supplemental service that In much of the PSTN, there exists a supplemental service that
translates calling party numbers into regular names, including the translates calling party numbers into regular names, including the
proper names of people and businesses, for rendering to the called proper names of people and businesses, for rendering to the called
user. These services (frequently termed 'Caller ID') provide a user. These services (frequently termed 'Caller ID') provide a
further attack surface for impersonation. The threat model described further attack surface for impersonation. The threat model described
in this document addresses only the calling party number, even though in this document addresses only the calling party number, even though
presenting a forged calling party number may cause a forged 'Caller presenting a forged calling party number may cause a chosen 'Caller
ID' name to be rendered to the user as well. Providing a verifiable ID' name to be rendered to the user as well. Providing a verifiable
calling party number therefore improve the security of Caller ID calling party number therefore improves the security of Caller ID
systems, but this threat model does not consider attacks specific to systems, but this threat model does not consider attacks specific to
Caller ID. Such attacks may be carried out against the databases Caller ID. Such attacks may be carried out against the databases
consulted by the terminating side of a call to provide Caller ID, or consulted by the terminating side of a call to provide Caller ID, or
by impersonators forging a particular calling party number in order by impersonators forging a particular calling party number in order
to present a misleading Caller ID to the user. to present a misleading Caller ID to the user.
2. Actors 2. Actors
2.1. Endpoints 2.1. Endpoints
There are two main categories of end-user terminals relevant to this There are two main categories of end-user terminals relevant to this
discussion, a dumb device (such as a 'black phone') or a smart discussion, a dumb device (such as a 'black phone') or a smart
device: device.
Dumb devices comprise a simple dial pad, handset and ringer, Dumb devices comprise a simple dial pad, handset and ringer,
optionally accompanied by a display that can render a limited optionally accompanied by a display that can render a limited
number of characters (typically, enough for a telephone number and number of characters (typically, enough for a telephone number and
an accompanying name, sometimes less). Although users interface an accompanying name, sometimes less). Although users interface
with these devices, the intelligence that drives them lives in the with these devices, the intelligence that drives them lives in the
service provider network. service provider network.
Smart devices are general purpose computers with some degree of Smart devices are general purpose computers with some degree of
programmability, and with the capacity to access the Internet and programmability, and with the capacity to access the Internet and
to render text, audio and/or images. This category includes smart to render text, audio and/or images. This category includes smart
phones, telephone applications on desktop and laptop computers, IP phones, telephone applications on desktop and laptop computers, IP
private branch exchanges, and so on. private branch exchanges, and so on.
There is a further category of automated terminals without an end There is a further category of automated terminals without an end
user. These include systems like voicemail services, which may user. These include systems like voicemail services, which may
provide a different set of services to a caller based solely on the provide a different set of services to a caller based solely on the
calling party's number, granting the mailbox owner access to a menu calling party's number, for example granting the mailbox owner access
while giving other callers only the ability to leave a message. to a menu while giving other callers only the ability to leave a
Though the capability of voicemail services varies widely, many today message. Though the capability of voicemail services varies widely,
have Internet access and advanced application interfaces (to render many today have Internet access and advanced application interfaces
'visual voicemail,' to automatically transcribe voicemail to email, (to render 'visual voicemail,' to automatically transcribe voicemail
and so on). to email, and so on).
There is a further category of automated terminals without an end
user. These include systems like voicemail services that consume the
calling party number without rendering it to a human. Though the
capability of voicemail services varies widely, many today have
Internet access and advanced application interfaces (to render
'visual voicemail,' to automatically transcribe voicemail to email,
and so on).
2.2. Intermediaries 2.2. Intermediaries
The endpoints of a traditional telephone call connect through The endpoints of a traditional telephone call connect through
numerous intermediary switches in the network. The set of numerous intermediary switches in the network. The set of
intermediary devices traversed during call setup between two intermediary devices traversed during call setup between two
endpoints is referred to as a call path. The length of the call path endpoints is referred to as a call path. The length of the call path
can vary considerably: it is possible in VoIP deployments for two can vary considerably: it is possible in VoIP deployments for two
endpoint entities to send traffic to one another directly, but, more endpoint entities to send traffic to one another directly, but, more
commonly, several intermediaries exist in a VoIP call path. One or commonly, several intermediaries exist in a VoIP call path. One or
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original protocol (elements like transaction-matching identifiers) original protocol (elements like transaction-matching identifiers)
and may need to transcode or otherwise alter identifiers as they and may need to transcode or otherwise alter identifiers as they
are rendered in the destination protocol. are rendered in the destination protocol.
This threat model assumes that intermediaries and gateways can This threat model assumes that intermediaries and gateways can
forward and retarget calls as necessary, which can result in a call forward and retarget calls as necessary, which can result in a call
terminating at a place the originator did not expect; this is an terminating at a place the originator did not expect; this is an
common condition in call routing. This is significant to the common condition in call routing. This is significant to the
solution space, because it limits the ability of the originator to solution space, because it limits the ability of the originator to
anticipate what the telephone number of the respondent will be (for anticipate what the telephone number of the respondent will be (for
more on the "unanticipated respondent" problem, see [10]). more on the "unanticipated respondent" problem, see [3]).
Furthermore, we assume that some intermediaries or gateways may, due Furthermore, we assume that some intermediaries or gateways may, due
to their capabilities or policies, discard calling party number to their capabilities or policies, discard calling party number
information, in whole or part. Today, many IP-PSTN gateways simply information, in whole or part. Today, many IP-PSTN gateways simply
ignore any information available about the caller in the IP leg of ignore any information available about the caller in the IP leg of
the call, and allow the telephone number of the PRI line used by the the call, and allow the telephone number of the PRI line used by the
gateway to be sent as the calling party number for the PSTN leg of gateway to be sent as the calling party number for the PSTN leg of
the call. A call might also gateway to a multifrequency network the call. A call might also gateway to a multifrequency network
where only a limited number of digits of automatic numbering where only a limited number of digits of automatic numbering
identification (ANI) data are signaled, for example. Some protocols identification (ANI) data are signaled, for example. Some protocols
may render telephone numbers in a way that makes it impossible for a may render telephone numbers in a way that makes it impossible for a
terminating side to parse or canonicalize a number. In these cases, terminating side to parse or canonicalize a number. In these cases,
providing authenticated identity may be impossible. This is not providing authenticated identity may be impossible, but this is not
however indicative of an attack or other security failure. indicative of an attack or other security failure.
2.3. Attackers 2.3. Attackers
We assume that an attacker has the following capabilities: We assume that an attacker has the following capabilities:
An attacker can create telephone calls at will, originating them An attacker can create telephone calls at will, originating them
either on the PSTN or over IP, and can supply an arbitrary calling either on the PSTN or over IP, and can supply an arbitrary calling
party number. party number.
An attacker can capture and replay signaling previously observed An attacker can capture and replay signaling previously observed
by it. [TBD: should this include an attacker that can capture by it.
signaling that isn't directly sent to it? Not a factor for
robocalling, but perhaps for voicemail hacking, say.]
An attacker has access to the Internet, and thus the ability to An attacker has access to the Internet, and thus the ability to
inject arbitrary traffic over the Internet, to access public inject arbitrary traffic over the Internet, to access public
directories, and so on. directories, and so on.
There are attack scenarios in which an attacker compromises There are attack scenarios in which an attacker compromises
intermediaries in the call path, or captures credentials that allow intermediaries in the call path, or captures credentials that allow
the attacker to impersonate a target. Those system-level attacks are the attacker to impersonate a target. Those system-level attacks are
not considered in this threat model, though secure design and not considered in this threat model, though secure design and
operation of systems to prevent these sorts of attacks is necessary operation of systems to prevent these sorts of attacks is necessary
for envisioned countermeasures to work. for envisioned countermeasures to work.
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This threat model also does not consider scenarios in which the This threat model also does not consider scenarios in which the
operators of intermediaries or gateways are themselves adversaries operators of intermediaries or gateways are themselves adversaries
who intentionally discard valid identity information (without a user who intentionally discard valid identity information (without a user
requesting anonymity) or who send falsified identity using their own requesting anonymity) or who send falsified identity using their own
credentials. The design of the credential system will however limit credentials. The design of the credential system will however limit
the scope of the credentials issued to carriers or national the scope of the credentials issued to carriers or national
authorities to those numbers that fall under their purview. authorities to those numbers that fall under their purview.
3. Attacks 3. Attacks
The uses of impersonation described in this section are broadly
divided into two categories: those where an attacker impersonates an
arbitrary identity in order to disguise their own, and those where an
attack will not succeed unless the attacker impersonates a specific
identity. At a high level, impersonation encourages targets to
answer attackers' calls and makes identifying attackers more
difficult. This section shows how concrete attacks based on those
different techniques might be launched.
3.1. Voicemail Hacking via Impersonation 3.1. Voicemail Hacking via Impersonation
A voicemail service allows users calling from their mobile phones A voicemail service allows users calling from their phones access to
access to their voicemail boxes on the basis of the calling party their voicemail boxes on the basis of the calling party number. If
number. If an attacker wants to access the voicemail of a particular an attacker wants to access the voicemail of a particular target, the
target, the attacker may try to impersonate the calling party number attacker may try to impersonate the calling party number using one of
using one of the scenarios described below. the scenarios described below.
This attack is closely related to attacks on similar automated
systems, potentially including banks, airlines, calling-card
services, conferencing providers, ISPs and other businesses that
fully or partly grant access to resources on the basis of the calling
party number. It would also be analogous to an attack where a human
is encouraged to answer a phone, or to divulge information once a
call is in progress, by seeing a familiar calling party number.
The envisioned countermeasures for this attack involve the voicemail The envisioned countermeasures for this attack involve the voicemail
treating calls that supply an authenticated identity differently from system treating calls that supply an authenticated identity
other calls. In the absence of identity, for example, a voicemail differently from other calls. In the absence of identity, for
service might enforce some other caller authentication policy example, a voicemail service might enforce some other caller
(perhaps requiring a PIN for caller authentication). Authenticated authentication policy (perhaps requiring a PIN for caller
identity alone provides a positive confirmation only when an identity authentication). Authenticated identity alone provides a positive
is claimed legitimately; the absence of authenticated identity here confirmation only when an identity is claimed legitimately; the
may not be evidence of malice, just of uncertainty. absence of authenticated identity here may not be evidence of malice,
just of uncertainty.
If the voicemail service could learn ahead of time that it should If the voicemail service could learn ahead of time that it should
expect authenticated identity from a particular number, that would expect authenticated identity from a particular number, that would
enable the voicemail service to adopt stricter policies for handling enable the voicemail service to adopt stricter policies for handling
a request without authenticated identity. Since users contact a a request without authenticated identity. Since users typically
voicemail service repeatedly, the service could for example remember contact a voicemail service repeatedly, the service could for example
which users usually sign their requests and require further remember which users usually sign their requests and require further
authentication mechanisms when signatures are absent. Alternatively, authentication mechanisms when signatures are absent. Alternatively,
issuers of credentials or other authorities could provide a service issuers of credentials or other authorities could provide a service
that informs verifiers that they should expect identity signatures in that informs verifiers that they should expect identity signatures in
calls from particular numbers. calls from particular numbers.
3.2. Unsolicited Commercial Calling from Impersonated Numbers 3.2. Unsolicited Commercial Calling from Impersonated Numbers
The unsolicited commercial calling, or for short robocalling, attack The unsolicited commercial calling, or for short robocalling, attack
is similar to the voicemail attack, except that the robocaller does is similar to the voicemail attack, except that the robocaller does
not need to impersonate the particular number controlled by the not need to impersonate the particular number controlled by the
target, merely some "plausible" number. A robocaller may impersonate target, merely some "plausible" number. A robocaller may impersonate
a number that is not an assignable number (for example, in the United a number that is not an assignable number (for example, in the United
States, a number beginning with 0), or an unassigned number. A States, a number beginning with 0), or an unassigned number. A
robocaller may change numbers every time a new call is placed, even robocaller may change numbers every time a new call is placed, even
selecting numbers randomly. selecting numbers randomly.
A closely related attack is sending unsolicited bulk commercial A closely related attack is sending unsolicited bulk commercial
messages via text messaging services. Almost always, these messages messages via text messaging services. These messages usually
originate on the Internet, though they may ultimately reach endpoints originate on the Internet, though they may ultimately reach endpoints
over traditional telephone network protocols or the Internet. While over traditional telephone network protocols or the Internet. While
most text messaging endpoints are mobile phones, increasingly most text messaging endpoints are mobile phones, increasingly
broadband residential services support text messaging as well. The broadband residential services support text messaging as well. The
originators of these messages typically impersonate a calling party originators of these messages typically impersonate a calling party
number, in some cases a "short code" specific to text messaging number, in some cases a "short code" specific to text messaging
services. services.
The envisioned countermeasures to robocalling are similar to those in The envisioned countermeasures to robocalling are similar to those in
the voicemail example, but there are significant differences. One the voicemail example, but there are significant differences. One
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should supply authenticated identity. If there were a service that should supply authenticated identity. If there were a service that
could inform the terminating side of that it should expect an could inform the terminating side of that it should expect an
identity signature in calls or texts from that number, however, that identity signature in calls or texts from that number, however, that
would also help in the robocalling case. would also help in the robocalling case.
When a human callee is to be alerted at call setup time, the time When a human callee is to be alerted at call setup time, the time
frame for executing any countermeasures is necessarily limited. frame for executing any countermeasures is necessarily limited.
Ideally, a user would not be alerted that a call has been received Ideally, a user would not be alerted that a call has been received
until any necessary identity checks have been performed. This could until any necessary identity checks have been performed. This could
however result in inordinate post-dial delay from the perspective of however result in inordinate post-dial delay from the perspective of
legitimate callers. Cryptographic operations and network operations legitimate callers. Cryptographic and network operations must be
must be minimized for these countermeasures to be practical. For minimized for these countermeasures to be practical. For text
text messages, a delay for executing anti-impersonation messages, a delay for executing anti-impersonation countermeasures is
countermeasures is much less likely to degrade perceptible service. much less likely to degrade perceptible service.
The eventual effect of these countermeasures would be to force The eventual effect of these countermeasures would be to force
robocallers to either block their caller identity, in which case end robocallers to either block their caller identity, in which case end
users could opt not to receive their calls or messages, or to force users could opt not to receive their calls or messages, or to force
robocallers to use authenticated identity for numbers traceable to robocallers to use authenticated identity for numbers traceable to
them, which would then allow for other forms of redress. them, which would then allow for other forms of redress.
3.3. Telephony Denial-of-Service Attacks
In the case of telephony denial-of-service (or TDoS) attacks, the
attack relies on impersonation in order to obscure the origin of an
attack that is intended to tie up telephone resources. By placing
constant telephone calls, an attacker renders a target number
unreachable by legitimate callers. These attaacks might target a
business, an individual or a public resource like emergency
responders; the attack may intend to extort the target or have other
motivations. Attack calls may be placed from a single endpoint, or
from multiple endpoints under the control of the attacker, and the
attacker may control endpoints in different administrative domains.
Impersonation in this case allows the attack to evade policies that
would block based on the originating number, and furthermore prevents
the victim from learning the perpetrator of the attack, or even the
originating service provider of the attacker.
As is the case with robocalling, the attacker typically does not have
to impersonate a specific number in order to launch a denial-of-
service attack. The number simply has to vary enough to prevent
simple policies from blocking the attack calls. An attacker may
however have a further intention to create the appearance that a
particular party is to blame for an attack, and in that case, the
attacker might want to impersonate a secondary target in the attack.
The envisioned countermeasures are twofold. First, as with
robocalling, ensuring that calling party numbers are assignable or
assigned will help mitigate unsophisticated attacks. Second, if
authenticated identity is supplied for legitimate calls, then
Internet endpoints or intermediaries can make effective policy
decisions in the middle of an attack by deprioritizing unsigned calls
when congestion conditions exist; signed calls, if accepted, have the
necessary accountability should it turn out they are malicious. This
could extend to include, for example, an originating network
observing a congestion condition for a destination number and perhaps
dropping unsigned calls that are clearly part of a TDoS attack. As
with robocalling, all of these countermeasures must execute in a
timely manner to be effective.
There are certain flavors of TDoS attacks, including those against
emergency responders, against which authenticated identity is
unlikely to be a successful countermeasure. These entities are
effectively obligated to attempt to respond to every call they
receive, and the absence of an authenticated identity signature, or
even the presence of an invalid signature, in many cases will not
remove that obligation.
4. Attack Scenarios 4. Attack Scenarios
The examples that follow rely on Internet protocols including SIP [1]
and WebRTC.
Impersonation, IP-PSTN Impersonation, IP-PSTN
An attacker on the Internet uses a commercial WebRTC service to send An attacker on the Internet uses a commercial WebRTC service to send
a call to the PSTN with a chosen calling party number. The service a call to the PSTN with a chosen calling party number. The service
contacts an Internet-to-PSTN gateway, which inserts the attacker's contacts an Internet-to-PSTN gateway, which inserts the attacker's
chosen calling party number into the CPN field of an IAM. When the chosen calling party number into the SS7 call setup message (the CPN
IAM reaches the terminating telephone switch, the terminal renders field of an IAM). When the call setup message reaches the
the attacker's chosen calling party number as the calling identity. terminating telephone switch, the terminal renders the attacker's
chosen calling party number as the calling identity.
Impersonation, PSTN-PSTN Impersonation, PSTN-PSTN
An attacker with a traditional PBX (connected to the PSTN through An attacker with a traditional PBX (connected to the PSTN through
ISDN) sends a Q.931 SETUP request with a chosen calling party number ISDN) sends a Q.931 SETUP request with a chosen calling party number
which a service provider inserts into the corresponding SS7 calling which a service provider inserts into the corresponding SS7 calling
party number (CPN) field of a call setup message (IAM). When the IAM party number (CPN) field of a call setup message (IAM). When the
reaches the endpoint switch, the terminal renders the attacker's call setup message reaches the endpoint switch, the terminal renders
chosen calling party number as the calling identity. the attacker's chosen calling party number as the calling identity.
Impersonation, IP-IP Impersonation, IP-IP
An attacker with an IP phone sends a SIP request to an IP-enabled An attacker with an IP phone sends a SIP request to an IP-enabled
voicemail service. The attacker puts a chosen calling party number voicemail service. The attacker puts a chosen calling party number
into the From header field value of the INVITE. When the INVITE into the From header field value of the INVITE. When the INVITE
reaches the endpoint terminal, the terminal renders the attacker's reaches the endpoint terminal, the terminal renders the attacker's
chosen calling party number as the calling identity. chosen calling party number as the calling identity.
Impersonation, IP-PSTN-IP Impersonation, IP-PSTN-IP
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attacker's INVITE reaches an Internet-to-PSTN gateway, which inserts attacker's INVITE reaches an Internet-to-PSTN gateway, which inserts
the attacker's chosen calling party number into the CPN of an IAM. the attacker's chosen calling party number into the CPN of an IAM.
That IAM then traverses the PSTN until (perhaps after a call That IAM then traverses the PSTN until (perhaps after a call
forwarding) it reaches another gateway, this time back to the IP forwarding) it reaches another gateway, this time back to the IP
realm, to an H.323 network. The PSTN-IP gateway puts takes the realm, to an H.323 network. The PSTN-IP gateway puts takes the
calling party number in the IAM CPN field and puts it into the SETUP calling party number in the IAM CPN field and puts it into the SETUP
request. When the SETUP reaches the endpoint terminal, the terminal request. When the SETUP reaches the endpoint terminal, the terminal
renders the attacker's chosen calling party number as the calling renders the attacker's chosen calling party number as the calling
identity. identity.
4.1. TBD: Solution-Specific Attacks 4.1. Solution-Specific Attacks
Solution-specific attacks are outside the scope of this document.
Some of the attacks that should be considered in the future include
the following:
[TBD: This is just forward-looking notes]
Attacks Against In-band Attacks Against In-band
Token replay Token replay
Removal of in-band signaling features Removal of in-band signaling features
Attacks Against Out-of-Band Attacks Against Out-of-Band
Provisioning Gargbage CPRs Provisioning Garbage CPRs
Data Mining Data Mining
Attacks Against Either Approach Attacks Against Either Approach
Attack on directories/services that say whether you should expect Attack on directories/services that say whether you should expect
authenticated identity or not authenticated identity or not
Canonicalization attack Canonicalization attacks
5. Acknowledgments 5. Acknowledgments
Stephen Kent, Brian Rosen, Alex Bobotek, Henning Schulzrinne, Hannes David Frankel, Penn Pfautz, Stephen Kent, Brian Rosen, Alex Bobotek,
Tschofenig, Cullen Jennings and Eric Rescorla provided key input to Henning Schulzrinne, Hannes Tschofenig, Cullen Jennings and Eric
the discussions leading to this document. Rescorla provided key input to the discussions leading to this
document.
6. IANA Considerations 6. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
7. Security Considerations 7. Security Considerations
This document provides a threat model and is thus entirely about This document provides a threat model and is thus entirely about
security. security.
8. Informative References 8. Informative References
[1] Peterson, J. and C. Jennings, "Enhancements for [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[4] Jennings, C., Peterson, J., and M. Watson, "Private [2] Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
November 2002.
[5] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012.
[6] Elwell, J., "Connected Identity in the Session Initiation
Protocol (SIP)", RFC 4916, June 2007.
[7] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC
3966, December 2004.
[8] Cooper, A., Tschofenig, H., Peterson, J., and B. Aboba,
"Secure Call Origin Identification", draft-cooper-iab-
secure-origin-00 (work in progress), November 2012.
[9] Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
Telephone Identity Problem Statement", draft-ietf-stir- Telephone Identity Problem Statement", draft-ietf-stir-
problem-statement-00 (work in progress), October 2013. problem-statement-01 (work in progress), December 2013.
[10] Peterson, J., "Retargeting and Security in SIP: A [3] Peterson, J., "Retargeting and Security in SIP: A
Framework and Requirements", draft-peterson-sipping- Framework and Requirements", draft-peterson-sipping-
retarget-00 (work in progress), February 2005. retarget-00 (work in progress), February 2005.
[11] Rosenberg, J., "Concerns around the Applicability of RFC
4474", draft-rosenberg-sip-rfc4474-concerns-00 (work in
progress), February 2008.
[12] Kaplan, H. and V. Pascual, "Loop Detection Mechanisms for
Session Initiation Protocol (SIP) Back-to- Back User
Agents (B2BUAs)", draft-ietf-straw-b2bua-loop-detection-02
(work in progress), September 2013.
[13] Barnes, M., Jennings, C., Rosenberg, J., and M. Petit-
Huguenin, "Verification Involving PSTN Reachability:
Requirements and Architecture Overview", draft-jennings-
vipr-overview-04 (work in progress), February 2013.
[14] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263, June
2002.
Author's Address Author's Address
Jon Peterson Jon Peterson
NeuStar, Inc. NeuStar, Inc.
1800 Sutter St Suite 570 1800 Sutter St Suite 570
Concord, CA 94520 Concord, CA 94520
US US
Email: jon.peterson@neustar.biz Email: jon.peterson@neustar.biz
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