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Security Concerns with IP Tunneling
RFC 6169

Internet Engineering Task Force (IETF)                       S. Krishnan
Request for Comments: 6169                                      Ericsson
Category: Informational                                        D. Thaler
ISSN: 2070-1721                                                Microsoft
                                                             J. Hoagland
                                                                Symantec
                                                              April 2011

                  Security Concerns with IP Tunneling

Abstract

   A number of security concerns with IP tunnels are documented in this
   memo.  The intended audience of this document includes network
   administrators and future protocol developers.  The primary intent of
   this document is to raise the awareness level regarding the security
   issues with IP tunnels as deployed and propose strategies for the
   mitigation of those issues.

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/rfc6169.

Copyright Notice

   Copyright (c) 2011 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

Krishnan, et al.             Informational                      [Page 1]
RFC 6169               Tunneling Security Concerns            April 2011

   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................2
   2. Tunnels May Bypass Security .....................................3
      2.1. Network Security Bypass ....................................3
      2.2. IP Ingress and Egress Filtering Bypass .....................5
      2.3. Source Routing after the Tunnel Client .....................6
   3. Challenges in Inspecting and Filtering Content of
      Tunneled Data Packets ...........................................7
      3.1. Inefficiency of Selective Network Filtering of All
           Tunneled Packets ...........................................7
      3.2. Problems with Deep Packet Inspection of Tunneled
           Data Packets ...............................................8
   4. Increased Exposure Due to Tunneling .............................9
      4.1. NAT Holes Increase Attack Surface ..........................9
      4.2. Exposure of a NAT Hole ....................................11
      4.3. Public Tunnels Widen Holes in Restricted NATs .............12
   5. Tunnel Address Concerns ........................................13
      5.1. Feasibility of Guessing Tunnel Addresses ..................13
      5.2. Profiling Targets Based on Tunnel Address .................14
   6. Additional Security Concerns ...................................15
      6.1. Attacks Facilitated by Changing Tunnel Server Setting .....15
   7. Mechanisms to Secure the Use of Tunnels ........................17
   8. Acknowledgments ................................................18
   9. Security Considerations ........................................18

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