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Versions: 00                                                            
INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 1

Network Working Group                              L. Amini
Internet-Draft                                 IBM Research
Expires: March 31, 2003
                                                  A. Barbir
                                            Nortel Networks

                                              Oskar Batuner
                                     Independent consultant

                                                     M. Day
                                              Cisco Systems

                                              O. Spatscheck
                                                  AT&T Labs

                                        Kobus van der Merwe
                                                  AT&T Labs

           Security Threat for Content Internetworking

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at

The list of Internet-Draft Shadow Directories can be accessed at

This Internet-Draft will expire on March 31, 2003 Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 2

      Security Threat for Content Internetworking


Content internetworking (also referred to as content distribution
internetworking, or CDI) is the technology for interconnecting content
networks. The CDI model allows for  interconnecting various Content
Networks. The internetworking  task requires request routing and
content distribution protocols. This document investigates the
security risks and threats  associated with the content
internetworking. Proposed remedies are viewed not as design
recommendations but more as illustrations of the nature of threats.

1. Introduction

Content internetworking (CDI) combines the resources of multiple
content networks (CN) to increase their scale and reach. At the core
of CDI are a request routing system and a distribution system. The
request-routing system (RRS) directs client requests to surrogates
and/or CNs that can best service the request. The internetworking of
CNs is performed through Content Internetworking Gateway (CIG). The
internetworking distribution system is responsible for moving content
from one Distribution CN to another Distribution CN.  Finally, the
accounting infrastructure tracks and collects data on
request-routing, distribution, and delivery functions within the CDN.
The details of the CDI model can be found in [1].

The use of CDI - as any new mechanism - introduces new security  risks
and threats to the internetworked CNs. Some of these threats are
specific to the CDI model, some are inherited from the CN systems.
This document covers both new and inherited threats with distinctions
made were appropriate.

The security risks within CDI can be classified along various
dimensions  including:

- the source of the threat ("insider" versus "outsider"),

- the level at which the attack occurs (network level attack versus
application level attack),

- the type of harm that results from an attack (harm to content, harm
to identity, harm to finances).

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 3

- the elements of the architecture attacked (e.g., the Distribution
System, the Request Routing System, the Accounting System, the
clients, or  publishers)

All of these dimensions are considered in this document (some in
greater detail) to develop a complete view of the  threat model for
content internetworking.  However, this document focuses only on those
threats specific to the content internetworking model.  It does not
consider, for example, the following issues:

- The security risks within an individual CN, such as denial of
service attacks on individual surrogates, are beyond the scope of
this document.

- Content security issues, such as the integrity of transformations
or adaptations performed on content, are outside the scope of the
current work.

- This document does not specify or recommend any particular
solutions.  In some cases however, potential threat mitigation steps
are given to help illustrate a given threat.

The remainder of this document is organized as follows.  We begin by
describing the CDI Trust Model, and distinguish between "insider"  and
"outsider" attacks.  Next, we broadly classify attacks as  occurring
at the network, content internetworking, or application  level, and
detail the resultant type of harm.  We refine this list  by detailing
how the attacks might be perpetrated on specific components  of the
CDI architecture, and potential mitigation steps.

1.1 Conventions used in this document

Key terms in ALL CAPS, except those qualified with explicit
citations, are defined in [1].

2. Content Internetworking Trust model

Relationships between CN's in the CDI model can be decomposed into
relationships between individual pairs comprising a CONTENT SOURCE and
a  CONTENT DESTINATION. The ORIGIN refers to the point at which
CONTENT enters  the CDI model, and therefore is a specific type of
CONTENT SOURCE.  The trust  model utilized within  CDI is based on a
transitive trust between a CONTENT  SOURCE and a CONTENT DESTINATION.
The transitive nature of the trust  originates from the need of an

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 4

pairs to deliver CONTENT to CLIENTs on the ORIGIN's behalf.

The trust model involves the following parties in trust relationships:

We will use the term TRUSTED PARTY to refer to a party involved in a
trust  relationship.

We begin by classifying security risks into two main categories:
threats from  "insiders," and threats from "outsiders."  Outsiders are
those entities that  have not established a trust relationship within
the content internetworking  system.  Insiders are TRUSTED PARTIES
that are participating in a trust  relationship within the content
internetworking system.

Threats from within the system may be intentional or unintentional.
Intentional threats refer to the ability of a TRUSTED PARTY of a CDI
relationship to mislead or harm, the party with which it has a trust
relationship. For example, the TRUSTED PARTY, a CONTENT DESTINATION,
might  misrepresent quality or quantity of the service provided to the
trusting party,  a CONTENT SOURCE. This is distinct from the case when
a TRUSTED PARTY's system  is compromised by an outsider, which is
covered as an "outsider" threat.

Unintentional threats refer to the ability of a TRUSTED PARTY, through
improper implementation or configuration resulting in bad system
behavior, to mislead or  harm the party with which it has a trust

Content internetworking allows for relationships whose terms and
conditions  are partially or completely established outside the
context of the content  internetworking protocols, and refers to these
relationships as NEGOTIATED  RELATIONSHIPS.  Just as trust
relationships established completely within the  context of content
internetworking protocols, NEGOTIATED RELATIONSHIPS can  result in
intentional or unintentional threats.

Threats from outside the system, or outsiders, may also be intentional
or unintentional.  Since unintentional threats from outsiders do not
rely on the trust model, and are not specific to the content
internetworking model, this document will consider only outsider
threats that are intentionally  perpetrated.

In this document, we will focus on intentional and unintentional
threats from  within the system, and intentional threats from outside
the system.

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 5

3. Threat classification by architectural level

In this section, we broadly classify threats according the
architectural level  -- network, content internetworking, or
application -- at which the threat  occurs.  We refer to threats
exploiting design or  implementation weaknesses of internetworking and
transport protocols (i.e.,  layer 3 and below of the TCP/IP protocol
suite) as network level threats.  We  refer to threats exploiting
weaknesses in content internetworking protocols as  content
internetworking level threats. We include in content internetworking
level attacks, threats against CONTENT distributed using CDI specific
protocols.  Finally, we refer to threats to applications that utilize
a content  internetworking system as application level threats.

Where appropriate, the type of harm that can result from an attack is
provided  to show the complex interaction between different threats
and/or attacks. For example, harm to content in the form of content
degradation or  content substitution might harm the finances of the
content provider which  might in turn harm the finances of the service
provider. A denial of service attack or theft of identity might have a
similar effect on parties involved  with CDI.

3.1 Network Level Threats.

The content internetworking model comprises CONTENT NETWORKs, which in
a network  device that performs at least some of its processing by
examining  CONTENT-related parts of network messages.  Examples of

In IP-based networks, a CONTENT NETWORK ELEMENT is a device whose
processing  depends on examining some or all of an IP packet's body.
As such, CONTENT  NETWORK ELEMENTs are vulnerable to many types of
network level attacks.    Examples of TCP/IP attacks include IP
spoofing  and session stealing. The  CERT Coordination Center [2]
maintains an extensive repository of Internet  Security

Harm specific to CONTENT NETWORK ELEMENTS, such as a CIG, achievable
by  hijacking a TCP/IP session includes the ability of outsiders to
inject  believable content distribution and  request routing messages
into the  communication between CIG peers. This may lead to the
injection of bogus  content or bogus routing information that may lead
to  the breaking of the  peer to peer connection. Any break in the

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 6

peer to peer  communication can  have a ripple effect on the request
routing system or the  distribution system  that could lead to
disrupted services to end users.

CONTENT NETWORK ELEMENTS are also susceptible to a number of security
threats  commonly associated with network infrastructure. These
threats  include snooping, denial of service, sabotage, vandalism,
industrial  espionage, theft of  service and inadequate system
configuration that leaves  unneeded ports and services open to the

3.2 . Content Internetworking Level Threats.

Content internetworking Level threats generally belong to one or more of the
following categories:

- denial of service
- content distortion
- threats to identity
- threats to privacy
- content theft
- security threats
- threats to finances

In the following subsections we elaborate on these threats and potential
resultant harm.

3.2.1 Denial of service threats.

At the Content Internetworking level, a denial of service (DoS) threat
can be  perpetrated on a number of levels.  For example, an attack
could be launched:

- specifically against a CONTENT SOURCE, thereby preventing any distribution
  from taking place
- against a content set, causing all CNs servicing this content set to be
- against all SURROGATES of a specific CN.

A CONTENT SOURCE distributing streaming content, due to its high
bandwidth  nature and, in the case of live streaming, limited
injection points, are  likely to be especially vulnerable to DoS

Misuse of a CN may make its facilities unavailable or available only
at  reduced functionality. Denial of service attacks can be targeted
at a CN  accounting system, distribution system, or request-routing

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 7 "Complexity threat": both CDN and CDI introduce many
components and  complex infrastructure. Malfunctioning of these
components and infrastructure  may result in DoS. Misconfigured request routing (unintentional or malicious)
may cause  request loss or looping and result in DoS. Conflicts between request routing and accounting mechanisms
may create a  DoS threat: a CN may refuse to deliver content because
the authorization system  treats a valid request as invalid (not
coming from an authorized customer). By redistributing the load between CNs CDI may cause DoS by
unintentionally overloading one of CNs. Usually CNs have a specific
(proprietary)  adaptive mechanisms for load balancing. CDI load
balancing mechanisms may be  inadequate/malfunction or be incompatible
with corresponding CDN load balancing. A CN may cause problems in another CN by sending
(unintentionally or  with malicious intent) more content than
advertised capacity permits. Corruption (intentional or non intentional) of security
related metadata  (authentication data) might result in DoS: CN or CDI
may refuse to perform a  legitimate service. False advertisement (unintentional or malicious) of
nonexistent  distribution/coverage capacity may result in failure of
several CNs.  Same problems may result when advertisement and usage
policy do not reflect  dynamic conditions. Incompatible request routing systems may cause problems
resulting in  DoS. Peering agreements may be vital for CDN functionality. This
makes  peering reliability a security issue. CIG (distribution CIG and
request routing  CIG) may introduce a single point of failure. Attack
on (or malfunctioning of)  a CIG may result in system disintegration
and DoS for both CNs.

3.2.2 Content distortion threats. An attacker may cause a CN to advertise bogus content,
e.g. replacing  proper content with bogus content either at the
injection point of the system  (CN or CDI) or inside elements of the
system (e.g. surrogates inside the CN).

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 8 A CN may provide bogus information, e.g. a rogue "CN"
inserting itself  in the distribution path between two CNs to monitor
and/or modify the content  that they exchange. A CN may advertise the availability of content which it
doesn't have  and can not distribute. This attacks can be the result
of malicious CIG  taking over the identity of a CIG to be able to
inject bogus info into  system, or a CIG that is compromised

3.2.3 Threats to user identity.

Identity/authentication threats may result from third party getting
access to authentication data of end user or system component
(surrogate, CIG) and this data permits unauthorized actions to be
performed.  Note that the last condition is essential: interception of
session initiation packets of replay-resistant secure authentication
protocol does not create such a threat.

Storage of security related data (user identities, passwords, etc.)
creates  an additional security threat.

3.2.4 Threats to privacy.  Privacy threats may result in personal user
information made available to third party without user's consent. A CN may inadvertently or maliciously expose  private
information (passwords, buying patterns, page views, and credit card
numbers) as it collects it and transits from surrogate to origin
and/or publisher. Accounting information transfer may jeopardize privacy. Privacy threats may result from differences in privacy policy
of  Publisher, CDN and CDI. Privacy and security threats from crossing jurisdiction
boundaries:  transfer and storage of sensitive privacy-related data
(accounting, logs),  transfer and storage of (secure) content and
distribution of content from a  different jurisdiction may create a
security threat due to different level  of legal protection.

3.2.5. Legal threats: by extending activities through jurisdiction
boundaries  CN and CDI may unintentionally violate local regulations
(privacy and security  policies).

3.2.6 Content theft.

Unauthorized access to non-public (secure or non-secure) content. For

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 9

secure content such unauthorized access clearly violates intention of
security system and usually constitutes a content theft (paid content,
proprietary data).

An example of unauthorized access to non-secure content is
interception of form data in not-secure transmission or direct access
to URL that is not supposed to be publicly available.

3.2.7 Security threats Unauthorized access to metadata that is not supposed to be
publicly available. This may include access to logs and accounting
data containing private user's information, access to configuration
data that may be used to facilitate future attacks and so on. Exposure of Security Settings: There may be risks that expose
client's  security settings when content is served from surrogates as
opposed to origin  servers. Since the location of the surrogate is
generally transparent to the  client, the client may be aware that its
protections are no longer enforced. Improper enforcement of Security Policy

Policy information regarding security of the client may not be
properly  propagated when the requests are directed to surrogates in a
CN that are  different from the origin server. Client passwords and
personal information  may be less secure.

3.2.8. Improper Carriage of Security Policies

Surrogate may not employ the same security policies and procedures as
the origin  server. This may expose the client private information to
access by unauthorized  entities. The same threat may also result if
the legal jurisdiction of the  surrogate is different from that of the
origin. Different implementation of security at Publisher, CDN and
CDI level may  create security threats Distribution of content from a different network location may
create a  security threat if client security policy depends on network
location ("Internet  Web Content Zone"). Transfer and storage of secure content create additional
security threats. The process of propagation of security policy and security
related data  (user identities, passwords, etc.) creates security

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 10

threats both at CDN and CDI  level.

3.2.9 Threats to finances

Delivery of inaccurate accounting information or malicious distortion
of this  information may cause financial harm to all participating
parties. The client may be inappropriately charged for viewing content
that was not  successfully accessed or delivered according to some QoS
criteria. If a CN or Publisher is unable to collect or receive correct
accounting  information they may be unable to collect compensation for

3.3 Application level threats.

TBD (section should include attacks targeting applications that
utilize  the content internetworking system)

4. Threats against specific elements of the CDI architecture

In this section, we refine the list of threats by detailing how the
attacks  might be perpetrated on specific components of the CDI
architecture. This  section is intended to be used input to specify
the security requirements for  the content distribution and request
routing protocols.

Along the dimension of threats against specific elements of the
architecture, threats against the accounting system should also be
noted. A detailed analysis of the threats against the accounting
system can however only be done within the framework of a specific
accounting system and is considered outside the scope of this document.

4.1 Threats to the Content Internetworking Gateway The CIG is the
connecting point for the CNs that are participating in the  CDI
model. CIGs from various CNs establish peer to peer relationships in
order to  exchange content distribution and request routing
information.  Threats on the CIG can be perpetrated at all levels, the
network, content  internetworking, and application level.

A CIG must be accessible at the network level from many  other
CIGs. The CIG  is vulnerable to any of the network level attacks
specified in Section 3.1.  The CIG is susceptible to network level

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 11

attacks from outsiders, which may or  may not be posing as the CIG of

4.2 Threats to Distribution System

Threats to distribution system from insiders can be intentional or the
result of  bad implementation. Outsiders can pose the same threats if
they acquire access  to the distribution system. The threats include:

4.2.1 Advertising of unavailable content.
4.2.3 Advertising of bad metrics that are associated with a given content.
4.2.4 Delivery of bad content to surrogates in the connected CN
4.2.5 Using badly formed messages for advertisements

4.3 Threats to Request Routing System

Threats to the request routing system from insiders or outsiders include:

4.3.1 Advertising of wrong metrics to force unfair or inaccurate
redirection to a given CN.
4.3.2 Redirection to a CN that does not have the content.
4.3.3 The introduction of loops in the requesting routing system.
4.3.4 Redirection to an inappropriate surrogate.
4.3.5 Forwarding request when no forwarding is appropriate.
4.3.6 Failing to forward requests when forwarding is appropriate.
4.3.7 Using badly formed messages for advertisements

h) TBD

5. CDI Security Threat Mitigation

The main security issues for the CDI model are focused on the Trust
model.  Insiders are TRUSTED PARTIES, while outsiders are not.

Threats from outsiders are primarily at the network level. There are
well known solutions to network level threats that are practiced in
the industry. In this work, it is recommended that the security of the
CONTENT NETWORK ELEMENTs at  the network level be enhanced  using
standard techniques and methods that minimize the risks of IP
spoofing, snooping, denial of service and session  stealing.

Threats at the content internetworking and application levels can be
mitigated  by using strong authentication and encryption
techniques. Therefore,  there may be the need to make strong
authentication and encryption a requirement  for the CDI model. IPSec

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 12

and TLS are solutions for this requirement. Regardless  of the choice
of the protocol, the solution must scale to accommodate large  number
of interconnected CNs.  Furthermore, it is recommended not to send
passwords in the clear.

To mitigate threats from insiders CDI must implement appropriate
monitoring,  signaling, logging, dynamic authorization and
verification mechanisms.  The following sections provide more detailed
guidelines for development of request routing and distribution
protocols for content internetworking.

5.1 Treatment of malformed messages

Malformed message can be the result of bad implementation or a
consequence of an  outside attack on a given CN whereby, the attacker
gains access of the peering  system. A Malformed messages is a message
that does not comply with the message  format for the distribution (or
request routing) protocol. A malformed message  may be a message that
has wrong content attributes in it or wrong IP footprint.  A malformed
IP or IPSec packet is not considered a malformed message.

In the event that a CN detect malformed messages terminating the
session appears  to be the only safe way to handle it. Terminating a
session does not mean  terminating the peering relationship. The
session can be restarted after  termination. If the problem of
malformed messages persists, the interconnected  CNs must verify the
cause of the problem and proceed with a solution.

The treatment of malformed messages is different than the case where a
peer  intentionally or unintentionally sends incorrect advertisements
which might lead  to incorrect selections. For example, a CN might
incorrectly advertise low load,  low cost and good coverage and
therefore attract a large proportion of traffic.  This problem can be
somewhat mitigated through filtering of advertisements and  local
policies but ultimately comes down to a trust relationship between

5.2 General Distribution and Request Routing Protocol Requirements

Based on the security threats that are faced by other peer-to-peer
based  protocols such as BGP, this section provide some guidelines
that should be used  during the design of the request routing and
content distribution protocols.

5.2.1 There should be a mechanism that provides strong protection of
the integrity,  freshness and source authenticity of the messages in

INTERNET-DRAFT      draft-ietf-cdi-threat-00.txt     Page 13

the protocol. Techniques  such as digital signature may be used.

5.2.2 There should be a mechanism to validate the authenticity of a
CN_Path value.

5.2.3 There should be a mechanism to use IP level protection that can
be used to  provide connectionless integrity, data origin
authentication, and secure authentication.

5.2.4 There should be a mechanism to protect the peer-to-peer
connection by  applying cryptographic protection at the TCP level to
provide connectionless  integrity and data origin authentication.


   [1]   Day, M., Cain, B. and G. Tomlinson, "A Model for Content
         Distribution Internetworking", January 2001.
   [2]   CERT Coordination Center (CERT/CC).