The Network Endpoint Assessment (NEA) Asokan Attack Analysis
RFC 6813

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Internet Engineering Task Force (IETF)                        J. Salowey
Request for Comments: 6813                                 Cisco Systems
Category: Informational                                         S. Hanna
ISSN: 2070-1721                                         Juniper Networks
                                                           December 2012

      The Network Endpoint Assessment (NEA) Asokan Attack Analysis

Abstract

   The Network Endpoint Assessment (NEA) protocols are subject to a
   subtle forwarding attack that has become known as the NEA Asokan
   Attack.  This document describes the attack and countermeasures that
   may be mounted.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6813.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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RFC 6813               NEA Asokan Attack Analysis          December 2012

Table of Contents

   1. Introduction ....................................................2
   2. NEA Asokan Attack Explained .....................................2
   3. Lying Endpoints .................................................4
   4. Countermeasures against the NEA Asokan Attack ...................4
      4.1. Identity Binding ...........................................4
      4.2. Cryptographic Binding ......................................5
           4.2.1. Binding Options .....................................5
   5. Conclusions .....................................................6
   6. Security Considerations .........................................6
   7. Informative References ..........................................7
   8. Acknowledgments .................................................7

1.  Introduction

   The Network Endpoint Assessment (NEA) [2] protocols are subject to a
   subtle forwarding attack that has become known as the NEA Asokan
   Attack.  This document describes the attack and countermeasures that
   may be mounted.  The Posture Transport (PT) protocols developed by
   the NEA working group, PT-TLS [5] and PT-EAP [6], include mechanisms
   that can provide cryptographic-binding and identity-binding
   countermeasures.

2.  NEA Asokan Attack Explained

   The NEA Asokan Attack is a variation on an attack described in a 2002
   paper written by Asokan, Niemi, and Nyberg [1].  Figure 1 depicts one
   version of the original Asokan attack.  This attack involves tricking
   an authorized user into authenticating to a decoy Authentication,
   Authorization, and Accounting (AAA) server, which forwards the
   authentication protocol from one tunnel to another, tricking the real
   AAA server into believing these messages originated from the
   attacker-controlled machine.  As a result, the real AAA server grants
   access to the attacker-controlled machine.

Salowey & Hanna               Informational                     [Page 2]
RFC 6813               NEA Asokan Attack Analysis          December 2012

                            +-------------+ ========== +----------+
                            |   Attacker  |-AuthProto--|AAA Server|
                            +-------------+ ========== +----------+
                                   |
                               AuthProto
                                   |
   +--------------+ ========== +----------------+
   |AuthorizedUser|-AuthProto--|Decoy AAA Server|
   +--------------+ ========== +----------------+

              Figure 1: One Example of Original Asokan Attack

   As described in the NEA Overview [2], the NEA Reference Model is
   composed of several nested protocols.  The Posture Attribute (PA)
   protocol is nested in the Posture Broker (PB) protocol, which is