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Network Working Group                                          D. Saucez
Internet-Draft                                                     INRIA
Intended status: Informational                                L. Iannone
Expires: August 29, 2013                               Telecom ParisTech
                                                          O. Bonaventure
                                        Universite catholique de Louvain
                                                       February 25, 2013


                         LISP Threats Analysis
                     draft-ietf-lisp-threats-04.txt

Abstract

   This document analyzes the potential threats against the security of
   the Locator/Identifier Separation Protocol (LISP) if deployed in the
   Internet.  This document proposes a set of recommendations to
   mitigate the identified security risks and keep a security level
   equivalent to what is observed in the Internet today (i.e., without
   LISP).  By following the recommendations of this draft a LISP
   deployment can achieve a security level that is comparable to the
   existing Internet architecture.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on August 29, 2013.

Copyright Notice

   Copyright (c) 2013 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



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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  4
   3.  On-path Attackers  . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Off-Path Attackers: Reference Environment  . . . . . . . . . .  5
   5.  Data-Plane Threats . . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  EID-to-RLOC Database Threats . . . . . . . . . . . . . . .  7
     5.2.  EID-to-RLOC Cache Threats  . . . . . . . . . . . . . . . .  7
       5.2.1.  EID-to-RLOC Cache poisoning  . . . . . . . . . . . . .  7
       5.2.2.  EID-to-RLOC Cache overflow . . . . . . . . . . . . . .  9
     5.3.  Attacks not leveraging on the LISP header  . . . . . . . . 10
     5.4.  Attacks leveraging on the LISP header  . . . . . . . . . . 10
       5.4.1.  Attacks using the Locator Status Bits  . . . . . . . . 10
       5.4.2.  Attacks using the Map-Version bit  . . . . . . . . . . 12
       5.4.3.  Attacks using the Nonce-Present and the Echo-Nonce
               bits . . . . . . . . . . . . . . . . . . . . . . . . . 13
       5.4.4.  Attacks using the Instance ID bits . . . . . . . . . . 14
   6.  Control Plane Threats  . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Attacks with Map-Request messages  . . . . . . . . . . . . 14
     6.2.  Attacks with Map-Reply messages  . . . . . . . . . . . . . 16
     6.3.  Gleaning Attacks . . . . . . . . . . . . . . . . . . . . . 17
   7.  Threats concerning Interworking  . . . . . . . . . . . . . . . 18
   8.  Threats with Malicious xTRs  . . . . . . . . . . . . . . . . . 19
   9.  Security of the Proposed Mapping Systems . . . . . . . . . . . 23
     9.1.  LISP+ALT . . . . . . . . . . . . . . . . . . . . . . . . . 23
     9.2.  LISP-DDT . . . . . . . . . . . . . . . . . . . . . . . . . 24
   10. Threats concerning LISP-MS . . . . . . . . . . . . . . . . . . 25
     10.1. Map Server . . . . . . . . . . . . . . . . . . . . . . . . 25
     10.2. Map Resolver . . . . . . . . . . . . . . . . . . . . . . . 26
   11. Security Recommendations . . . . . . . . . . . . . . . . . . . 28
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 30
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 30
   14. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 30
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 31
     15.2. Informative References . . . . . . . . . . . . . . . . . . 31
   Appendix A.  Document Change Log . . . . . . . . . . . . . . . . . 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34




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1.  Introduction

   The Locator/ID Separation Protocol (LISP) is defined in [RFC6830].
   The present document assesses the security level and identifies
   security threats in the LISP specification if LISP is deployed in the
   Internet (i.e., a public non-trustable environment).  As a result of
   the performed analysis, the document determines the severity of the
   threats and proposes recommendations to reach the same level of
   security in LISP than in Internet today (e.g., without LISP).

   The document is composed of three main parts: the first discussing
   the LISP data-plane; while the second discussing the LISP control-
   plane.  The final part summarizes the recommendations to prevent the
   identified threats.

   The LISP data-plane consists of LISP packet encapsulation,
   decapsulation, and forwarding and includes the EID-to-RLOC Cache and
   EID-to-RLOC Database data structures used to perform these
   operations.

   The LISP control-plane consists in the mapping distribution system,
   which can be one of the mapping distribution systems proposed so far
   (e.g., [RFC6830], [I-D.ietf-lisp-ddt], [RFC6836], [RFC6833],
   [I-D.meyer-lisp-cons], and [RFC6837]), and the Map-Request, Map-
   Reply, Map-Register, and Map-Notification messages.

   This document does not consider all the possible uses of LISP as
   discussed in [RFC6830].  The document focuses on LISP unicast,
   including as well LISP Interworking [RFC6832], LISP-MS [RFC6833],
   LISP Map-Versioning [RFC6834], and briefly considering the ALT
   mapping system described in [RFC6836] and the Delegated Database Tree
   mapping system described in [I-D.ietf-lisp-ddt].  The reading of
   these documents is a prerequisite for understanding the present
   document.

   Unless otherwise stated, the document assumes a generic IP service
   and does not discuss the difference, from a security viewpoint,
   between using IPv4 or IPv6.

   This document has identified several threats on LISP in the case of
   public deployments.  However, most of the threats can be prevented
   with careful deployment and configuration.  Moreover, several threats
   are introduced by optimization techniques that can be deactivated in
   public deployments of LISP without alteration of its functioning as
   these techniques are designed for LISP deployments in private
   trustable environments.  Finally, this document has not identified
   any threats that would require a change in the LISP protocol or
   architecture.



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2.  Definition of Terms

   Severity level: this document specifies the severity level of every
   identified threat.  We identified four severity levels for the
   threats.

   Level 0:  the threat is not introduced by LISP and is equivalent to
         what is encountered without LISP.

   Level 1:  the threat is introduced by LISP but can be neutralized by
         configuration or deployment techniques, i.e., LISP protocol and
         architecture does not need to be reconsidered for public
         deployment.

   Level 2:  the threat is introduced by LISP but can be avoided by
         deactivating the feature in public deployment.

   Level 3:  the threat is introduced by LISP and cannot be avoided
         without changing the LISP specification or architecture.

   The present document does not introduce any other new term, compared
   to the main LISP specification.  For a complete list of terms please
   refer to [RFC6830].


3.  On-path Attackers

   On-path attackers are attackers that are able to capture and modify
   all the packets exchanged between an Ingress Tunnel Router (ITR) and
   an Egress Tunnel Router (ETR).  To cope with such an attacker,
   cryptographic techniques such as those used by IPSec ([RFC4301]) are
   required.  As with IP, LISP relies on higher layer cryptography to
   secure packet payloads from on path attacks, so we do not consider
   on-path attackers in this document.

   Mobile IP has also considered time-shifted attacks from on-path
   attackers.  A time-shifted attack is an attack where the attacker is
   temporarily on the path between two communicating hosts.  While it is
   on-path, the attacker sends specially crafted packets or modifies
   packets exchanged by the communicating hosts in order to disturb the
   packet flow (e.g., by performing a man in the middle attack).  An
   important issue for time-shifted attacks is the duration of the
   attack once the attacker has left the path between the two
   communicating hosts.  We do not consider time-shifted attacks in this
   document.






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4.  Off-Path Attackers: Reference Environment

   Throughout this document we consider the reference environment shown
   in the figure below.  There are two hosts attached to LISP routers:
   HA and HB.  HA is attached to the two LISP xTRs LR1 and LR2, which in
   turn are attached to two different ISPs.  HB is attached to the two
   LISP xTRs LR3 and LR4.  HA and HB are the EIDs of the two hosts.
   LR1, LR2, LR3, and LR4 are the RLOCs of the xTRs.

                 +-----+
                 | HA  |
                 +-----+
                    | EID: HA
                    |
                -----------------
                    |          |
                 +-----+    +-----+
                 | LR1 |    | LR2 |
                 +-----+    +-----+
                    |          |
                    |          |
                 +-----+    +-----+
                 |ISP1 |    |ISP2 |
                 +-----+    +-----+
                    |          |
                 +----------------+     +-----+
                 |                |-----| SA  |
                 |                |     +-----+
                 |    Internet    |
                 |                |     +-----+
                 |                |-----| NSA |
                 +----------------+     +-----+
                    |          |
                 +-----+    +-----+
                 | LR3 |    | LR4 |
                 +-----+    +-----+
                    |          |
                -------------------
                               |
                               | EID: HB
                            +-----+
                            | HB  |
                            +-----+

                        Figure 1: Reference Network

   We consider two off-path attackers with different capabilities:




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   SA  is an off-path attacker that is able to send spoofed packets,
       i.e., packets with a different source IP address than its
       assigned IP address.  SA stands for Spoofing Attacker.

   NSA is an off-path attacker that is only able to send packets whose
       source address is its assigned IP address.  NSA stands for Non
       Spoofing Attacker.

   It should be noted that with LISP, packet spoofing is slightly
   different than in the current Internet.  Generally the term "spoofed
   packet" indicates a packet containing a source IP address that is not
   the one of the actual originator of the packet.  Since LISP uses
   encapsulation, the spoofed address could be in the outer header as
   well as in the inner header, this translates in two types of
   spoofing:

   EID Spoofing:  the originator of the packet puts in it a spoofed EID.
         The packet will be normally encapsulated by the ITR of the site
         (or a PITR if the source site is not LISP enabled).

   RLOC Spoofing:  the originator of the packet generates directly a
         LISP-encapsulated packet with a spoofed source RLOC.

   Note that the two types of spoofing are not mutually exclusive,
   rather all combinations are possible and could be used to perform
   different kind of attacks.

   In the reference environment, both SA and NSA attackers are capable
   of sending LISP encapsulated data packets and LISP control packets.
   This means that SA is able to perform both RLOC and EID spoofing
   while NSA can only perform EID spoofing.  They may also send other
   types of IP packets such as ICMP messages.  We assume that both
   attackers can query the LISP mapping system (e.g., through a public
   Map Resolver) to obtain the mappings for both HA and HB.


5.  Data-Plane Threats

   This section discusses threats and attacks related to the LISP data-
   plane.  More precisely, we discuss the operations of encapsulation,
   decapsulation, and forwarding as well as the content of the EID-to-
   RLOC Cache and EID-to-RLOC Database as specified in the original LISP
   document ([RFC6830]).

   We start considering the two main data structures of LISP, namely the
   EID-to-RLOC Database and the EID-to-RLOC Cache.  Then, we look at the
   data plane attacks that can be performed by a spoofing off-path
   attacker (SA) and discuss how they can be mitigated by LISP xTRs.  In



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   this analysis, we assume that the LR1 and LR2 (resp. LR3 and LR4)
   xTRs maintain an EID-to-RLOC Cache that contains the required mapping
   entries to allow HA and HB to exchange packets.

5.1.  EID-to-RLOC Database Threats

   The EID-to-RLOC Database on each xTR maintains the set of mappings
   related to the EID-Prefixes that are "behind" the xTR.  Where
   "behind" means that at least one of the xTR's globally visible IP
   addresses is a RLOC for those EID-Prefixes.

   As described in [RFC6830], the EID-to-RLOC Database content is
   determined by configuration.  This means that the only way to attack
   this data structure is by gaining privileged access to the xTR.  As
   such, it is out of the scope of LISP to propose any mechanism to
   protect routers and, hence, it is no further analyzed in this
   document.

   Severity level 0.

5.2.  EID-to-RLOC Cache Threats

   The EID-to-RLOC Cache (also called the Map-Cache) is the data
   structure that stores a copy of the mappings retrieved from a remote
   ETR's mapping database via the LISP control plane.  Attacks against
   this data structure could happen either when the mappings are first
   installed in the cache (see also Section 6) or by corrupting
   (poisoning) the mappings already present in the cache.

   Severity level 2.  The severity level of EID-to-RLOC Cache Threats
   depends on the attack vector as described below.

5.2.1.  EID-to-RLOC Cache poisoning

   The content of the EID-to-RLOC Cache could be poisoned by spoofing
   LISP encapsulated packets.  Examples of EID-to-RLOC Cache poisoning
   are:

   Fake mapping:  The cache contains entirely fake mappings that do not
         originate from an authoritative mapping server.  This could be
         achieved either through gleaning as described in Section 6.3 or
         by attacking the control-plane as described in Section 6.

   EID Poisoning:  The EID-Prefix in a specific mapping is not owned by
         the originator of the entry.  Similarly to the previous case,
         this could be achieved either through gleaning as described in
         Section 6.3 or by attacking the control-plane as described in
         Section 6.



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   EID redirection/RLOC poisoning:  The EID-Prefix in the mapping is not
         bound to (located by) the set of RLOCs present in the mapping.
         This could result in packets being redirected elsewhere,
         eavesdropped, or even black-holed.  Note that not necessarily
         all RLOCs are fake/spoofed.  The attack works also if only part
         of the RLOCs, the highest priority ones, is compromised.
         Again, this could be achieved either through the gleaning as
         described in Section 6.3 or by attacking the control-plane as
         described in Section 6.

   Reachability poisoning:  The reachability information stored in the
         mapping could be poisoned, redirecting the packets to a subset
         of the RLOCs (or even stopping it if locator status bits are
         all set to 0).  If reachability information is not verified
         through the control-plane this attack could be achieved by
         sending a spoofed packet with swapped or all locator status
         bits reset.  The same result could be obtained by attacking the
         control-plane as described in Section 6.  Depending on how the
         RLOC reachability information is stored on the router, the
         attack could impact only one mapping or all the mappings that
         share the same RLOC.

   Traffic Engineering information poisoning:  The LISP protocol defines
         two attributes associated to each RLOC in order to perform
         inbound Traffic Engineering (TE), namely priority and weight.
         By injecting fake TE attributes, the attacker is able to break
         load balancing policies and concentrate all the traffic on a
         single RLOC or put more load on a RLOC than what is expected,
         creating congestion.  It is even possible to block the traffic
         if all the priorities are set to 255 (special value indicating
         not to use the RLOC).  Corrupting the TE attributes could be
         achieved by attacking the control-plane as described in
         Section 6.

   Mapping TTL poisoning:  The LISP protocol associates a Time-To-Live
         to each mapping that, once expired, allows to delete a mapping
         from the EID-to-RLOC Cache (or forces a Map-Request/Map-Reply
         exchange to refresh it if still needed).  By injecting fake TTL
         values, an attacker could either shrink the EID-to-RLOC Cache
         (using very short TTL), thus creating an excess of cache miss
         causing a DoS on the mapping system, or it could increase the
         size of the cache by putting very high TTL values, up to a
         cache overflow (see Section 5.2.2).  Corrupting the TTL could
         be achieved by attacking the control-plane as described in
         Section 6.  Long TTL could be used in fake mappings to increase
         attack duration.





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   Instance ID poisoning:  The LISP protocol allows using a 24-bit
         identifier to select the forwarding table to use on the
         decapsulating ETR to forward the decapsulated packet.  By
         spoofing this attribute the attacker might cause traffic to be
         either dropped or decapsulated and then placed into the
         incorrect VRF at the destination ETR.  Corrupting the Instance
         ID attribute could be achieved by attacking the control-plane
         as described in Section 6.

   Map-Version poisoning:  The LISP protocol offers the option to
         associate a version number to mappings ([RFC6834]).  The LISP
         header can transport source and destination map-versions,
         describing which version of the mapping have been used to
         select the source and the destination RLOCs of the LISP
         encapsulated packet.  By spoofing this attribute the attacker
         is able to trigger Map-Request on the receiving ETR.
         Corrupting the Map-Version attribute could be achieved either
         by attacking the control-plane as described in Section 6 or by
         using spoofed packets as described in Section 5.4.2.

   If the ITR's map-cache is compromised (likely via compromising the
   LISP control-plane) it is possible that traffic in the data-plane may
   be redirected (encapsulated to the wrong destination) a or dropped by
   the ITR.

   If data-plane redirection is of a critical concern, then deploying
   some sort of IPSEC or TLS based security on a layer above LISP (just
   like you would on top of IP) is recommended.

5.2.2.  EID-to-RLOC Cache overflow

   Depending on how the EID-to-RLOC Cache is managed (e.g., Least
   Recently Used - LRU vs. Least Frequently Used - LFU) and depending on
   its size, an attacker could try to fill the cache with fake mappings.
   Once the cache is full, some mappings will be replaced by new fake
   ones, causing traffic disruption.

   This could be achieved either through gleaning as described in
   Section 6.3 or by attacking the control-plane as described in
   Section 6.

   Another way to generate an EID-to-RLOC Cache overflow is by injecting
   mapping with a fake and very large TTL value.  In this case the cache
   will keep a large amount of mappings ending with a completely full
   cache.  This type of attack could also be performed through the
   control-plane.





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5.3.  Attacks not leveraging on the LISP header

   We first consider an attacker that sends packets without exploiting
   the LISP header, i.e., with the N, L, E, V, and I bits reset
   ([RFC6830]).

   To inject a packet in the HA-HB flow, a spoofing off-path attacker
   (SA) could send a LISP encapsulated packet whose source is set to LR1
   or LR2 and destination LR3 or LR4.  The packet will reach HB as if
   the packet was sent by host HA.  This is not different from today's
   Internet where a spoofing off-path attacker may inject data packets
   in any flow.  Several existing techniques could be used by hosts to
   prevent such attacks from affecting established flows, e.g.,
   [RFC4301] and [I-D.ietf-tcpm-tcp-security].

   On the other hand, a non-spoofing off-path attacker (NSA) could only
   send a packet whose source address is set to its assigned IP address.
   The destination address of the encapsulated packet could be LR3 or
   LR4.  When the LISP ETR that serves HB receives the encapsulated
   packet, it can consult its EID-to-RLOC Cache and verify that NSA is
   not a valid source address for LISP encapsulated packets containing a
   packet sent by HA.  This verification is only possible if the ETR
   already has a valid mapping for HA.  Otherwise, and to avoid such
   data packet injection attacks, the LISP ETR should reject the packet
   and possibly query the mapping system to obtain a mapping for the
   encapsulated source EID (HA).

   Severity level 1: use well known anti-spoofing techniques and
   configure ETRs to verify the that RLOCs and EIDs are consistent with
   the entries in the EID-to-RLOC Cache.

5.4.  Attacks leveraging on the LISP header

   The main LISP document [RFC6830] defines several flags that modify
   the interpretation of the LISP header in data packets.  In this
   section, we discuss how an off-path attacker could exploit this LISP
   header.

   Severity level 2.  The severity level of attacks leveraging on the
   LISP header depends on the attack vector as described below.

5.4.1.  Attacks using the Locator Status Bits

   When the L bit is set to 1, it indicates that the second 32-bits
   longword of the LISP header contains the Locator Status Bits.  In
   this field, each bit position reflects the status of one of the RLOCs
   mapped to the source EID found in the encapsulated packet.  In
   particular, a packet with the L bit set and all Locator Status Bits



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   set to zero indicates that none of the locators of the encapsulated
   source EID are reachable.  The reaction of a LISP ETR that receives
   such a packet is not clearly described in [RFC6830].

   A spoofing off-path attacker (SA) could send a data packet with the L
   bit set to 1, all Locator Status Bits set to zero, a spoofed source
   RLOC (e.g.  LR1), destination LR3, and containing an encapsulated
   packet whose source is HA.  If LR3 blindly trusts the Locator Status
   Bits of the received packet it will set LR1 and LR2 as unreachable,
   possibly disrupting ongoing communication.

   Locator Status Bits could be blindly trusted only in secure
   environments.  In the general unsecured Internet environment, the
   safest practice for xTRs is to confirm the reachability change
   through the control plane (e.g., RLOC probing).  In the above
   example, LR3 should note that something has changed in the Locator
   Status Bits and query the mapping system (assuming it is trusted) in
   order to confirm status of the RLOCs of the source EID.

   A similar attack could occur by setting only one Locator Status Bit
   to 1, e.g., the one that corresponds to the source RLOC of the
   packet.

   If a non-spoofing off-path attacker (NSA) sends a data packet with
   the L bit set to 1 and all Locator Status Bits set to zero, this
   packet will contain the source address of the attacker.  Similarly as
   in Section 5.3, if the xTR accepts the packet without checking the
   EID-to-RLOC Cache for a mapping that binds the source EID and the
   source RLOC of the received packet, then the same observation like
   for the spoofing attacker (SA) apply with the difference that instead
   of complete disruption, the traffic will flow through only one RLOC,
   possibly resulting in a DoS attack.

   Otherwise, if the xTR does make the check through the EID-to-RLOC
   Cache, it should reject the packet because its source address is not
   one of the addresses listed as RLOCs for the source EID.
   Nevertheless, in this case a Map-Request should be sent, which could
   be used to perform Denial of Service attacks.  Indeed an attacker
   could frequently change the Locator Status Bits in order to trigger a
   large amount of Map-Requests.  Rate limitation, as described in
   [RFC6830], if implemented in a very simple way a single bucket for
   all triggered control plane messages, does not allow sending high
   number of such a request, resulting in the attacker saturating the
   rate with these spoofed packets.

   Severity level 2: to avoid any risk, Locator Status Bits should be
   deactivated in public deployments of LISP.  Deactivating LSB does not
   reduce LISP functionality.



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5.4.2.  Attacks using the Map-Version bit

   The optional Map-Version bit is used to indicate whether the low-
   order 24 bits of the first 32 bits longword of the LISP header
   contain a Source and Destination Map-Version.  When a LISP ETR
   receives a LISP encapsulated packet with the Map-Version bit set to
   1, the following actions are taken:

   o  It compares the Destination Map-Version found in the header with
      the current version of its own mapping, in the EID-to-RLOC
      Database, for the destination EID found in the encapsulated
      packet.  If the received Destination Map-Version is smaller (i.e.,
      older) than the current version, the ETR should apply the SMR
      procedure described in [RFC6830] and send a Map-Request with the
      SMR bit set.

   o  If a mapping exists in the EID-to-RLOC Cache for the source EID,
      then it compares the Map-Version of that entry with the Source
      Map-Version found in the header of the packet.  If the stored
      mapping is older (i.e., the Map-Version is smaller) than the
      source version of the LISP encapsulated packet, the xTR should
      send a Map-Request for the source EID.

   A spoofing off-path attacker (SA) could use the Map-Version bit to
   force an ETR to send Map-Request messages.  The attacker could
   retrieve the current source and destination Map-Version for both HA
   and HB.  Based on this information, it could send a spoofed packet
   with an older Source Map-Version or Destination Map-Version.  If the
   size of the Map-Request message is larger than the size of the
   smallest LISP-encapsulated packet that could trigger such a message,
   this could lead to amplification attacks (see Section 6.1).  However,
   [RFC6830] recommends to rate limit the Map-Request messages that are
   sent by an xTR.  This prevents the amplification attack, but there is
   a risk of Denial of Service attack if an attacker sends packets with
   Source and Destination Map-Versions that frequently change.  In this
   case, and depending on the implementation of the rate limitation
   policy, the ETR might consume its entire rate by sending Map-Request
   messages in response to these spoofed packets.

   A non-spoofing off-path attacker (NSA) could not success in such an
   attack if the destination xTR rejects the LISP encapsulated packets
   that are not sent by one of the RLOCs mapped to the included source
   EID.  If it is not the case, the attacker could be able to perform
   attacks concerning the Destination Map Version number as for the
   spoofing off-path attacker (SA).

   Severity level 1: the correct deployment of anti-spoofing and rate
   limitation techniques prevents the attacks leveraging on the Map-



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   Version.

5.4.3.  Attacks using the Nonce-Present and the Echo-Nonce bits

   The Nonce-Present and Echo-Nonce bits are used when verifying the
   reachability of a remote ETR.  Assume that LR3 wants to verify that
   LR1 receives the packets that it sends.  LR3 can set the Echo-Nonce
   and the Nonce-Present bits in LISP data encapsulated packets and
   include a random nonce in these packets.  Upon reception of these
   packets, LR1 will store the nonce sent by LR3 and echo it when it
   returns LISP encapsulated data packets to LR3.

   A spoofing off-path attacker (SA) could interfere with this
   reachability test by sending two different types of packets:

   1.  LISP data encapsulated packets with the Nonce-Present bit set and
       a random nonce and the appropriate source and destination RLOCs.

   2.  LISP data encapsulated packets with the Nonce-Present and the
       Echo-Nonce bits both set and the appropriate source and
       destination RLOCs.  These packets will force the receiving ETR to
       store the received nonce and echo it in the LISP encapsulated
       packets that it sends.

   The first type of packet should not cause any major problem to ITRs.
   As the reachability test uses a 24 bits nonce, it is unlikely that an
   off-path attacker could send a single packet that causes an ITR to
   believe that the ETR it is testing is reachable while in reality it
   is not reachable.  To increase the success likelihood of such attach,
   the attacker should created a massive amount of packets carrying all
   possible nonce values.  However, "flood attack" can be easily
   detected and blocked.

   The second type of packet could be exploited to create a Denial of
   Service attack against the nonce-based reachability test.  Consider a
   spoofing off-path attacker (SA) that sends a continuous flow of
   spoofed LISP data encapsulated packets that contain the Nonce-Present
   and the Echo-Nonce bit and each packet contains a different random
   nonce.  The ETR that receives such packets will continuously change
   the nonce that it returns to the remote ITR.  If the remote ITR
   starts a nonce-reachability test, this test may fail because the ETR
   has received a spoofed LISP data encapsulated packet with a different
   random nonce and never echoes the real nonce.  In this case the ITR
   will consider the ETR not reachable.  The success of this test will
   of course depend on the ratio between the amount of packets sent by
   the legitimate ITR and the spoofing off-path attacker (SA).

   Packets sent by a non-spoofing off-path attacker (NSA) can cause



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   similar problem if no check is done with the EID-to-RLOC Cache (see
   Section 5.3 for the EID-to-RLOC Cache check).  Otherwise, if the
   check is performed the packets will be rejected by the ETR that
   receives them and cannot cause problems.

   Severity level 2: to avoid any problem, echo nonce should be
   deactivated.  Deactivating echo-nonce does not reduce LISP
   functionality as it is an optimization for symmetric data flow path
   and because other techniques exist to test the reachability of a
   RLOC.

5.4.4.  Attacks using the Instance ID bits

   LISP allows to carry in its header a 24-bits value called "Instance
   ID" and used on the ITR to indicate which private Instance ID has
   been used for encapsulation, while on the ETR can be used to select
   the forwarding table used for forwarding the decapsulated packet.

   Even if an off-path attacker could randomly guess a valid Instance ID
   value, there is no LISP specific problem.  Obviously the attacker
   could be now able to reach hosts that are only reachable through the
   routing table identified by the attacked Instance ID, however, end-
   system security is out of the scope of this document.  Nevertheless,
   access lists can be configured to protect the network from Instance
   ID based attacks.

   Severity level 1: the correct deployment of access control lists and
   firewalls prevent the attacks leveraging on the Instance ID.


6.  Control Plane Threats

   In this section, we discuss the different types of attacks that could
   occur when an off-path attacker sends control plane packets.  We
   focus on the packets that are sent directly to the ETR and do not
   analyze the particularities of a LISP mapping system.  The LISP+ALT
   and LISP-DDT mapping systems are discussed in Section 9.

   Severity level 2.  The severity level of attacks on the LISP control-
   plane depends on the attack vector as described below.

6.1.  Attacks with Map-Request messages

   An off-path attacker could send Map-Request packets to a victim ETR.
   In theory, a Map-Request packet is only used to solicit an answer and
   as such it should not lead to security problems.  However, the LISP
   specification [RFC6830] contains several particularities that could
   be exploited by an off-path attacker.



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   The first possible exploitation is the P bit.  The P bit is used to
   probe the reachability of remote ETRs.  In our reference environment,
   LR3 could probe the reachability of LR1 by sending a Map-Request with
   the P bit set.  LR1 would reply by sending a Map-Reply message with
   the P bit set and the same nonce as in the Map-Request message.

   A spoofing off-path attacker (SA) could use the P bit to force a
   victim ETR to send a Map-Reply to the spoofed source address of the
   Map-Request message.  As the Map-Reply can be larger than the Map-
   Request message, there is a risk of amplification attack.
   Considering only IPv6 addresses, a Map-Request can be as small as 40
   bytes, considering one single ITR address and no Mapping Protocol
   Data.  The Map-Reply instead has a size of O(12 + (R * (28 + N *
   24))) bytes, where N is the maximum number of RLOCs in a mapping and
   R the maximum number of records in a Map-Reply.  Since up to 255
   RLOCs can be associated to an EID-Prefix and 255 records can be
   stored in a Map-Reply, the maximum size of a Map-Reply is thus above
   1 MB showing a size factor of up to 39,193 between the message sent
   by the attacker and the message sent by the ETR.  These numbers are
   however theoretical values not considering transport layer
   limitations and it is more likely that the reply will contain only
   one record with at most a dozen of locators, giving an amplification
   factor around 8.

   Any ISP with a large number of potential RLOCs for a given EID-Prefix
   should carefully ponder the best trade-off between the number of
   RLOCs through which it wants that the EID is reachable and the
   consequences that an amplification attack can produce.

   It should be noted that the maximum rate of Map-Reply messages should
   apply to all Map-Replies and also be associated to each destination
   that receives Map-Reply messages.  Otherwise, a possible
   amplification attack could be launched by a spoofing off-path
   attacker (SA) as follows.  Consider an attacker SA and EID-Prefix
   192.0.2.0/24 and a victim ITR.  To amplify a Denial of Service attack
   against the victim ITR, SA could send spoofed Map-Request messages
   whose source EID addresses are all the addresses inside 192.0.2.0/24
   and source RLOC address is the victim ITR.  Upon reception of these
   Map-Request messages, the ETR would send large Map-Reply messages for
   each of the addresses inside p/P back to the victim ITR.

   If a non-spoofing off-path attacker (NSA) sends a Map-Request with
   the P bit set, it will receive a Map-Reply with the P bit set.  This
   does not raise security issues besides the usual risk of overloading
   a victim ETR by sending too many Map-Request messages.

   The Map-Request message may also contain the SMR bit.  Upon reception
   of a Map-Request message with the SMR bit, an ETR must return to the



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   source of the Map-Request message a Map-Request message to retrieve
   the corresponding mapping.  This raises similar problems as the P bit
   discussed above except that as the Map-Request messages are smaller
   than Map-Reply messages, the risk of amplification attacks is
   reduced.  This is not true anymore if the ETR append to the Map-
   Request messages its own Map-Records.  This mechanism is meant to
   reduce the delay in mapping distribution since mapping information is
   provided in the Map-Request message.

   Severity level 1: the correct deployment of anti-spoofing and rate
   limitation techniques prevents the attacks leveraging the Map-Request
   message.

   Furthermore, appending Map-Records to Map-Request messages represents
   a major security risk since an off-path attacker could generate a
   (spoofed or not) Map-Request message and include in the Map-Reply
   portion of the message mapping for EID prefixes that it does not
   serve.  This could lead to various types of redirection and denial of
   service attacks.  An xTR should not process the Map-Records
   information that it receives in a Map-Request message.  As it is a
   performance optimization, we recommend to deactivate this
   functionality in public LISP deployments.

   Severity level 2: to avoid any risk, appending Map-Records to Map-
   Request messages should be deactivated in public deployments of LISP.
   Deactivating appending Map-Records to Map-Request messages does not
   reduce LISP functionality.

6.2.  Attacks with Map-Reply messages

   In this section we analyze the attacks that could occur when an off-
   path attacker sends directly Map-Reply messages to ETRs without using
   one of the proposed LISP mapping systems.

   There are two different types of Map-Reply messages:

   Positive Map-Reply:  These messages contain a Map-Record binding an
         EID-Prefix to one or more RLOCs.

   Negative Map-Reply:  These messages contain a Map-Record for an EID-
         Prefix with an empty locator-set and specifying an action,
         which may be either Drop, natively forward, or Send Map-
         Request.

   Positive Map-Reply messages are used to map EID-Prefixes onto RLOCs.
   Negative map-reply messages are used to indicate non-lisp prefixes.
   ITRs can, if needed, be configured to send all traffic destined for
   non-lisp prefixes to a Proxy-ETR.



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   Most of the security of the Map-Reply messages depends on the 64 bits
   nonce that is included in a Map-Request and returned in the Map-
   Reply.  An ETR must never accept a Map-Reply message whose nonce does
   not match one of the pending Map-Request messages.  If an ETR does
   not accept Map-Reply messages with an invalid nonce, the risk of
   attack is acceptable given the size of the nonce (64 bits).

   The nonce only confirms that the map-reply received was sent in
   response to a map-request sent, it does not validate the contents of
   that map-reply.

   In addition, an attacker could perform EID-to-RLOC Cache overflow
   attack by de-aggregating (i.e., splitting an EID prefix into
   artificially smaller EID prefixes) either positive or negative
   mappings.

   Severity level 1: the correct deployment of anti-spoofing techniques
   prevents attacks leveraging the Map-Reply message.

6.3.  Gleaning Attacks

   A third type of attack involves the gleaning mechanism proposed in
   [RFC6830] and discussed in [Saucez09].  In order to reduce the time
   required to obtain a mapping, [RFC6830] allows an ITR to learn a
   mapping from the LISP data encapsulated packets and the Map-Request
   packets that it receives.  LISP data encapsulated packet contains a
   source RLOC, destination RLOC, source EID and destination EID.  When
   an ITR receives a data encapsulated packet coming from a source EID
   for which it does not already know a mapping, it may insert the
   mapping between the source RLOC and the source EID in its EID-to-RLOC
   Cache.  Gleaning could also be used when an ITR receives a Map-
   Request as the Map-Request also contains a source EID address and a
   source RLOC.  Once a gleaned entry has been added to the EID-to-RLOC
   cache, the LISP ITR sends a Map-Request to retrieve the mapping for
   the gleaned EID from the mapping system.  [RFC6830] recommends
   storing the gleaned entries for only a few seconds.

   The first risk of gleaning is the ability to temporarily hijack an
   identity.  Consider an off-path attacker that wants to temporarily
   hijack host HA's identity and send packets to host HB with host HA's
   identity.  If the xTRs that serve host HB do not store a mapping for
   host HA, a non-spoofing off-path attacker (NSA) could send a LISP
   encapsulated data packet to LR3 or LR4.  The ETR will store the
   gleaned entry and use it to return the packets sent by host HB to the
   attacker.  In parallel, the ETR will send a Map-Request to retrieve
   the mapping for HA.  During a few seconds or until the reception of
   the Map-Reply, host HB will exchange packets with the attacker that
   has hijacked HA's identity.  Note that the attacker could in parallel



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   send lots of Map-Requests or lots of LISP data encapsulated packets
   with random sources to force the xTR that is responsible for host HA
   to send lots of Map-Request messages in order to force it to exceed
   its rate limit for control plane messages.  This could further delay
   the arrival of the Map-Reply message on the requesting ETR.

   Gleaning also introduces the possibility of a man-in-the-middle
   attack.  Consider an off-path attacker that knows that hosts HA and
   HB that resides in different sites will exchange information at time
   t.  An off-path attacker could use this knowledge to launch a man-in-
   the-middle attack if the xTRs that serve the two hosts do not have
   mapping for the other EID.  For this, the attacker sends to LR1
   (resp. LR3) a LISP data encapsulated packet whose source RLOC is its
   IP address and contains an IP packet whose source is set to HB (resp.
   HA).  The attacker chooses a packet that will not trigger an answer,
   for example the last part of a fragmented packet.  Upon reception of
   these packets, LR1 and LR3 install gleaned entries that point to the
   attacker.  As explained above, the attacker could, at the same time,
   send lots of packets to LR1 and LR3 to force them to exhaust their
   control plane rate limit.  This will extend the duration of the
   gleaned entry.  If host HA establishes a flow with host HB at that
   time, the packets that they exchange will first pass through the
   attacker.

   In both cases, the attack only lasts for a few seconds (unless the
   attacker is able to exhaust the rate limitation).  However it should
   be noted that today a large amount of packets might be exchanged
   during even a small fraction of time.

   Severity level 2: to avoid any risk, gleaning should be deactivated
   in public deployments of LISP.  Deactivating gleaning does not reduce
   LISP functionality.


7.  Threats concerning Interworking

   [RFC6832] defines two network elements to allow LISP and non-LISP
   sites to communicate, namely the Proxy-ITR and the Proxy-ETR.  The
   Proxy-ITR encapsulates traffic from non-LISP sites in order to
   forward it toward LISP sites, while the Proxy-ETR decapsulates
   traffic arriving from LISP sites in order to forward it toward non-
   LISP sites.  For these elements some of the attack based on the LISP
   specific header are not possible, for the simple reason that some of
   the fields cannot be used due to the unidirectional nature of the
   traffic.

   The Proxy-ITR has functionality similar to the ITR, however, its main
   purpose is to encapsulate packets arriving from the DFZ in order to



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   reach LISP sites.  This means that it is no bound to any particular
   EID-Prefix, hence no mapping exists and no mapping can be configured
   in the EID-to-RLOC Database.  This means that the Proxy-ITR element
   itself is not able to check whether or not the arriving traffic has
   the right to be encapsulated or not.  To limit Proxy-ITRs being used
   as relays for attacks, Proxy-ITRs operators are encouraged to
   implement best practices for data plane access control on the Proxy-
   ITRs and the border of the network, that is the edge of the scope of
   the Proxy-ITR's announcement of the EID-Prefix.  On the other side,
   the Proxy-ITR is meant to encapsulate only packets that are destined
   to one of the LISP sites it is serving.  This is the case for
   instance for a service provider selling Proxy-ITR services.  For this
   purpose a static EID-to-RLOC Cache can be configured in order to
   encapsulate only valid packets.  In case of a cache-miss no Map-
   Request needs to be sent and the packet can be silently dropped.

   The Proxy-ETR has functionality similar to the ETR, however, its main
   purpose is to inject un-encapsulated packet in the DFZ in order to
   reach non-LISP-Sites.  This means that since there is no specific
   EID-Prefix downstream, it has no EID-to-RLOC Database that can be
   used to check whether or not the destination EID is part of its
   domain.  In order to avoid for the Proxy-ETR to be used as relay in a
   DoS attack it is preferable to configure the EID-to-RLOC Cache with
   static entries used to check if an encapsulated packet coming from a
   specific RLOC and having a specific source EID is actually allowed to
   transit through the Proxy-ETR.  This is also important for services
   provider selling Proxy-ETR service to actually process only packets
   arriving from its customers.  However, in case of cache-miss no Map-
   Request needs to be sent, rather the packet can be silently dropped
   since it is not originating from a valid site.  The same drop policy
   should be used for packets with an invalid source RLOC or a valid
   source RLOC but an invalid EID.

   As it is the case without LISP, the addition of public proxies offers
   opportunities to attackers to commit attacks.  LISP interworking does
   not open new threats compared to other interworking techniques based
   on public proxies.

   Severity level 0: the careful configuration of PETR and PITR combined
   with the deployment of anti-spoofing techniques mitigates the attacks
   leveraging interworking and provides the same level of severity as
   interworking techniques in the Internet.


8.  Threats with Malicious xTRs

   In this section, we discuss the threats that could be caused by
   malicious xTRs.  We consider the reference environment below where



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   EL1 is a malicious or compromised xTR.  This malicious xTR serves a
   set of hosts that includes HC.  The other xTRs and hosts in this
   network play the same role as in the reference environment described
   in Section 4.

                 +-----+
                 | HA  |
                 +-----+
                    | EID: HA
                    |
                -----------------
                    |          |
                 +-----+    +-----+
                 | LR1 |    | LR2 |
                 +-----+    +-----+
                    |          |
                    |          |
                 +-----+    +-----+
                 |ISP1 |    |ISP2 |
                 +-----+    +-----+
                    |          |
                 +----------------+     +-----+  |
                 |                |-----| EL1 |--|
                 |                |     +-----+  |
                 |    Internet    |              |  +-----+
                 |                |              |--| HC  |
                 |                |              |  +-----+
                 +----------------+                 EID: HC
                    |          |
                 +-----+    +-----+
                 | LR3 |    | LR4 |
                 +-----+    +-----+
                    |          |
                -------------------
                               |
                               | EID: HB
                            +-----+
                            | HB  |
                            +-----+

              Figure 2: Malicious xTRs' Reference Environment

   Since xTRs are cornerstone in the LISP architecture, malicious xTRs
   are probably the most serious threat to the LISP control plane from a
   security viewpoint.  Indeed, the impact of compromised LISP Control
   Plane can be severe, and the most effective way to attack any multi-
   organizational control plane is from within the system itself.  To
   understand the problem, let us consider the following scenario.  Host



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   HC and HB exchange packets with host HA.  As all these hosts reside
   in LISP sites, LR1 and LR2 store mappings for HB and HC.  Thus, these
   xTRs may need to exchange LISP control plane packets with EL1, e.g.,
   to perform reachability tests or to refresh expired mappings (e.g.,
   if HC's mapping has a small TTL).

   A first threat against the LISP control plane is when EL1 replies to
   a legitimate Map-Request message sent by LR1 or LR2 with a Map-Reply
   message that contains an EID-Prefix that is larger than the prefix
   owned by the site attached to EL1.  For instance if the prefix owned
   by EL1 is 192.0.2.0/25 but the Map-Reply contain a mapping for
   192.0.2.0/24.  This could allow EL1 to attract packets destined to
   other EIDs than the EIDs that are attached to EL1.  This attack is
   called an "overclaiming" attack.

   A malicious ETR might fragment its eid-to-rloc database and then
   instigate traffic to its site, therefore creating state on the
   corresponding ITR's map-cache.  This attack is called de-aggregation
   attack.

   Overclaiming attack could be combined with de-aggregation to succeed
   a LISP Cache poisoning attack and prefix hijacking.  For example, if
   the EID prefix of the attacker is 192.0.2.0/25, it cannot provide a
   mapping for the EID prefix 192.0.2.128/25 (i.e., it cannot hijack the
   prefix).  However, since a Map-Reply can contain several map records,
   it is possible to hijack such a prefix by providing as well a mapping
   for it.  To this end, the attacker could send a Map-Reply with an EID
   prefix that covers at the same time the requested EID and the
   hijacked target prefix.  Continuing the previous example, if the
   requested mapping is for EID 192.0.2.1, and the target hijack prefix
   is 192.0.2.128/25, the Map-Reply will contain a map record for
   192.0.2.0/24 and a map record for 192.0.2.128/25.  Such a reply is
   considered legitimate according to the requested EID, while the map
   record of the hijacked prefix may lead to traffic redirection/
   disruption and ITR's Cache poisoning.

   Another variant of the overclaiming attack is a Denial of Service
   attack by sending a Negative Map-Reply message for a larger prefix
   without any locator and with the Drop action.  Such a Negative Map-
   Reply indicates that the ETR that receives it should discard all
   packets.

   By enabling [I-D.ietf-lisp-sec], overclaiming attacks are mitigated
   under the assumption that the mapping system can be trusted.  This
   assumption is equivalent to the general assumption that the control-
   plane is trustable in BGP meaning that the threat is not more severe
   than what is observed today.  In addition, at the time of the writing
   all Map Server implementations are configured with the minimal prefix



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   allowed to be register by their customers such that a customer cannot
   register an overclaimed attack.  Therefore, if mappings are always
   retrieved via the mapping system with LISP-Sec activated and if Map-
   Registers are cryptographically protected as recommended in the
   specifications, overclaiming attack is not possible.

   Another concern with malicious xTRs is the possibility of Denial of
   Service attacks.  A first attack is the flooding attack that was
   described in [I-D.bagnulo-lisp-threat].  This attack allows a
   malicious xTR to redirect traffic to a victim.  The malicious xTR
   first defines a mapping for HC with two RLOCs: its own RLOC (EL1) and
   the RLOC of the victim (e.g., LR3).  The victim's RLOC is set as
   unreachable in the mapping.  HC starts a large download from host HA.
   Once the download starts, the malicious xTR updates its Locator
   Status Bits, changes the mapping's version number or sets the SMR bit
   such that LR1 updates its EID-to-RLOC Cache to send all packets
   destined to HC to the victim's RLOC.  Instead of downloading from HA,
   the attacker could also send packets that trigger a response (e.g.,
   ICMP, TCP SYN, DNS request, ...) to HA.  HA would then send its
   response and its xTR would forward it to the victim's RLOC.

   An important point to note about this flooding attack is that it
   reveals a limitation of the LISP architecture.  A LISP ITR relies on
   the received mapping and possible reachability information to select
   the RLOC of the ETR that it uses to reach a given EID or block of
   EIDs.  However, if the ITR made a mistake, e.g., due to
   misconfiguration, wrong implementation, or other types of errors and
   has chosen a RLOC that does not serve the destination EID, there is
   no easy way for the LISP ETR to inform the ITR of its mistake.  A
   possible solution is to enforce an ETR to perform a reachability test
   with the selected ITR as soon as there is LISP encapsulated traffic
   between the two.  We recommend to never use reachability information
   without verifying them first.

   Note that the attacks discussed in this section are for documentation
   purpose only.  Malicious xTRs are either somehow directly deployed by
   attackers or the result of attackers gaining privileged access to
   existing xTRs.  As such, it is out of the scope of LISP to propose
   any mechanism to protect routers or to avoid their deployments with
   malicious intentions.

   Severity level 2: the correct deployment of anti-spoofing and rate
   limiting techniques combined with LISP-Sec and Map-Register
   authentication prevents threats caused by malicious xTRs, as long as
   mappings are always retrieved via a trustable mapping system.  In
   addition reachability information should never been used without
   being verified first.




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9.  Security of the Proposed Mapping Systems

9.1.  LISP+ALT

   One of the assumptions in [RFC6830] is that the mapping system is
   more secure than sending Map-Request and Map-Reply messages directly.
   We analyze this assumption in this section by analyzing the security
   of the ALT mapping system.

   The ALT mapping system is basically a manually configured overlay of
   GRE tunnels between ALT routers.  BGP sessions are established
   between ALT routers that are connected through such tunnels.  An ALT
   router advertises the EID prefixes that it serves over its BGP
   sessions with neighboring ALT routers and the EID-Prefixes that it
   has learned from neighboring ALT routers.

   The ALT mapping system is in fact a discovery system that allows any
   ALT router to discover the ALT router that is responsible for a given
   EID-Prefix.  To obtain a mapping from the ALT system, an ITR sends a
   packet containing a Map-Request on the overlay.  This Map-Request is
   sent inside a packet whose destination is the requested EID.  The
   Map-Request is routed on the overlay until it reaches the ALT router
   that advertised initially the prefix that contains the requested EID.
   This ALT router then replies directly by sending a Map-Reply to the
   RLOC of the requesting ITR.

   The security of the ALT mapping system depends on many factors,
   including:

   o  The security of the intermediate ALT routers.

   o  The validity of the BGP advertisements sent on the ALT overlay.

   ALT routers are interconnected with tunnels, the usage of secured
   tunnels prevents BGP advertisements to be altered, dropped, or added
   by on-path or off path attackers.  If a high level of security is
   required, works in the SIDR working group that develop security
   solutions for BGP ([RFC6480]) could be applied to LISP+ALT.

   The security of the intermediate ALT routers is another concern.  A
   malicious intermediate ALT router could manipulate the received BGP
   advertisements and also answer to received Map-Requests without
   forwarding them to their final destination on the overlay.  This
   could lead to various types of redirection attacks.  Note that in
   contrast with a regular IP router that could also manipulate in
   transit packets, when a malicious or compromised ALT router replies
   to a Map-Request, it can redirect legitimate traffic for a long
   period of time by sending an invalid Map-Reply message.  Thus, the



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   impact of a malicious ALT router could be more severe than a
   malicious router in today's Internet.  BGP is also weak in case of a
   router involved in the BGP topology is compromised.

   Severity level 1: configuring correctly the Map Servers, Map
   Revolvers, and ALT routers with filters corresponding to their
   customer cones provides the same security level as in BGP.  If more
   security is necessary, cryptography must be used to validate the
   mappings themselves.

9.2.  LISP-DDT

   The LISP Delegated Database Tree (LISP-DDT) mapping system is
   proposed as an alternative for LISP+ALT [I-D.ietf-lisp-ddt].  LISP-
   DDT is a hierarchical distributed database for EID-to-RLOC mappings.
   Each DDT node is configured with an EID prefix it is authoritative
   for, as well as the RLOC addresses and EID prefixes of the LISP-DDT
   nodes that are authoritative for more specific EID prefix.  In LISP-
   DDT, mappings are retrieved iterative.  A Map Resolver that needs to
   locate a mapping traverses the tree of DDT nodes contacting them one
   after another until the leaf of the DDT tree that is authoritative
   for the longest matching EID prefix for the mapping's EID is reached.
   The Map Resolver traverses the hierarchy of LISP-DDT nodes by sending
   Map-Requests, with the LISP-DDT-originated bit set, to LISP-DDT
   nodes.  The Map Resolver first contacts the root of the hierarchy.
   When a LISP-DDT node receives a Map-Request, it replies to the Map
   Resolver with a Map-Referral that contains the list of the locators
   of its children that are authoritative of a prefix that covers the
   EID in the Map-Request.  The Map Resolver then contacts one of these
   children that will return, at its turn, a Map-Referral.  This
   procedure is iteratively executed until a Map-Referral marked with
   the done flag is received.  The locators that appear in a referral
   with the done flag are those of the authoritative ETRs for the EID in
   the Map-Request.  At that moment, the Map Resolver falls back to its
   normal behavior and sends a Map-Request to the ETR in order for the
   ITR to obtain the mapping.  It is worth to mention that the Map
   Resolver can cache the referrals to avoid traversing all the whole
   hierarchy for all mapping retrievals.

   The operation in LISP-DDT is different from ALT and thus it does not
   present the same threats as LISP+ALT.  As a first difference, LISP-
   DDT natively includes security specification providing data origin
   authentication, data integrity protection and secure EID prefix
   delegation.  Hence, these aspects are no further explored in this
   document.

   However, threats exist for LISP-DDT as well.  For instance, a DoS
   attack could be performed on the mapping infrastructure by asking to



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   retrieve a large amount of mappings at the same time, hence, the
   importance of carefully dimensioning the topology of the DDT
   hierarchy.

   If an attacker manages to compromise a LISP-DDT node it could send
   fake referrals to the Map Resolver and then control the mappings
   delivered to the ITRs.  Furthermore, the effects of such an attack
   could be longer than the attack itself if the Map Resolver caches the
   referrals.

   Severity level 1: the correct deployment of anti-spoofing and rate
   limiting techniques combined with embedded security features of LISP-
   DDT prevent attacks leveraging LISP-DDT.


10.  Threats concerning LISP-MS

   LISP-MS ([RFC6833] specifies two network elements, namely the Map
   Server and the Map Resolver, that are meant to be used by xTRs to
   access the mapping system.  The advantage is clearly the fact that
   even if the mapping system changes in time xTRs do not need to change
   anything since they deal only with Map Servers and Map Resolvers.
   This includes the security aspects, since no change in the local
   security policies is needed.

10.1.  Map Server

   Map Server is used to dispatch Map-Request coming from the mapping
   system to ETRs that are authoritative for the EID in the request.  To
   this end it is necessary that ETRs register their mappings to the Map
   Server.  This allows the Map Server to know toward which ETR to
   forward Map-Requests and also to announce the EID-prefixes of the
   registered mappings in the mapping system.

   LISP uses a shared key approach in order to protect the Map Server
   and grant registration rights only to ETRs that have a valid key.
   Shared key must be used to protect both the registration message and
   the Map-Notify message when used.  The mechanism used to share the
   key between a Map Server and an ETRs must be secured to avoid that a
   malicious nodes catch the key and uses it to send forged Map-Register
   message to the Map Server.  A forged Map-Register message could be
   used to attract Map-Request and thus provide invalid Map-Replies or
   the redirect Map-Requests to a target to mount a DoS attack.

   More subtle attacks could be carried out only in the case of
   malicious ETRs.  A malicious ETR could register an invalid RLOC to
   divert Map-Requests to a target ETR and succeed a DoS attack on it.
   To avoid this kind of attack, the Map Server must check that the



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   registered RLOCs belong to ETRs authoritative for the registered EID
   prefix.  Such check can be done by sending and explicit Map-Request
   for the EID to the ETRs in the mapping and check that replies with a
   Map-Reply.  If the ETRs return a valid Map-Reply, the RLOC belongs to
   an authoritative ETR.  Note that this does not protect against
   malicious ETRs that create forged Map-Replies.  Stronger techniques
   for RLOC check are presented in [I-D.saucez-lisp-mapping-security].

   Similarly to the previous case, a malicious ETR could register an
   invalid EID-prefix to attract Map-Requests or to redirect them to a
   target to mount a DoS attack.  To avoid this kind of attack, the Map
   Server must check that the prefixes registered by an ETR belong to
   that ETR.  One method could be to manually configure EID-prefix
   ranges that can be announced by ETRs.
   [I-D.saucez-lisp-mapping-security] present alternative techniques to
   verify the prefix claimed by an ETR.

   Severity level 1: the correct deployment of anti-spoofing and rate
   limiting techniques combined with usage of Map-Register
   authentication prevents attacks leveraging the Map Server.

10.2.  Map Resolver

   Map Resolvers receive Map-Requests, typically from ITRs, and use the
   mapping system to find a mapping for the EID in the Map-Request.  It
   can work in two modes:

   Non-Caching Mode:  The resolver just forwards the Map-Request to the
         mapping system, which will take care of delivering the request
         to an authoritative ETR.  The latter will send back a Map-Reply
         directly to the ITR that has originally issued the request.

   Caching Mode:  The resolver will generate a new Map-Request and send
         it to the mapping system.  In this way it will receive the
         corresponding reply, store a local copy in a cache, and send
         back a reply to the original requester.  Since all requested
         mappings are locally cached, before actually making a request
         to the mapping system it performs a lookup in the local cache
         and in case of an hit, it send back a reply without querying
         the mapping system.

   In its basic mode, i.e., non-caching mode, the Map Resolver does not
   keep state, hence, the only direct form of attack is a DoS attack,
   where an attacker (or a group of attackers) could try to exhaust
   computational power by flooding the resolver with requests.  Common
   filtering techniques and BCP against DoS attacks could be applied in
   this case.




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   Nonetheless, attackers could use resolvers as relay for DoS attacks
   against xTRs.  An off-path spoofing attacker could generate a high
   load of requests to a set of resolvers, hence distributing the load
   in order to avoid to be blocked.  All this requests can use a
   specific EID that makes all the requests to be forwarded to a
   specific ETR, which, as a result, will be victim of a DDoS attack.
   Similarly, the attacker could use a spoofed source address making all
   the replies to converge to one single ITR, which, as a result, will
   be victim of a DDoS attack.  Such scenarios are not specific to LISP,
   but rather a common problem of every query infrastructure, hence the
   same BCP can be applied in order to limit the attacks.

   When functioning in caching-mode, the resolver will use the same type
   of cache than ITRs.  Due to its similarity with the ITRs' cache the
   analysis provided in Section 5.2 holds also in this case.  However,
   an important difference exists: this cache is not used for packet
   encapsulation but only for quick replies when new requests arrive.
   Therefore, as the caching-mode is only an optimization, the attacks
   that aim at filling the Map Resolver cache have a less severe impact
   on the traffic.  The usage of LISP-Sec prevents ITR to obtain invalid
   mappings.  It is worth noting that caching is not used in current
   implementations as it makes mapping synchronization hard for mobile
   devices.

   When Map Resolvers are used as front-end of the LIS-DDT mapping
   system they may be exposed to another variant of DoS.  Indeed, the
   iterative operation of the Map Resolver on the DDT hierarchy implies
   that it has to maintain state about the ITR that requested the
   mapping, this in order to send the final Map-Request to the ETR on
   behalf of the ITR.  An attacker might leverage on this to fill the
   Map Resolver memory and then cause a DoS.  Rate limiting can be used
   to present this attack.

   The question may arise on whether a Kaminsky-like attack is possible
   for an off-path attacker against ITRs sending requests to a certain
   resolver.  The 64-bits nonce present in every message has been
   introduced in the LISP specification to avoid such kind of attack.
   There has been discussion within the LISP Working Group on the
   optimal size of the nonce, and it seems that 64-bits provides
   sufficient protection.

   A possible way to limit the above-described attacks is to introduce
   strong identification in the Map-Request/Map-Reply by using the
   Encapsulated Control Message with authentication enabled
   [I-D.ietf-lisp-sec].

   Severity level 1: the correct deployment of anti-spoofing and rate
   limiting techniques combined with LISP-Sec and Map-Register



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   authentication prevent attacks leveraging Map Resolver.


11.  Security Recommendations

   Different deployments of LISP may have different security
   requirements.  The recommendations in this document aim at mitigating
   threats in in public deployments of LISP.

   To mitigate the impact of attacks against LISP in public deployments,
   the following recommendations should be followed.

   First, the use of some form of filtering can help in avoid or at
   least mitigate some types of attacks.

   o  On ETRs, packets should be decapsulated only if the destination
      EID is effectively part of the EID-Prefix downstream the ETR.
      Further, still on ETRs, packets should be decapsulated only if a
      mapping for the source EID is present in the EID-to-RLOC Cache and
      has been obtained through the mapping system (not gleaned).

   o  On ITRs, packets should be encapsulated only if the source EID is
      effectively part of the EID-Prefix downstream the ITR.  Further,
      still on ITRs, packets should be encapsulated only if a mapping
      obtained from the mapping system is present in the EID-to-RLOC
      Cache (no Data-Probing).

   Note that this filtering, since complete mappings need to be
   installed in both ITRs and ETRs, can introduce higher connection
   setup latency and hence potentially more packets drops due to the
   lack of mappings in the EID-to-RLOC Cache.

   While the gleaning mechanism allows starting encapsulating packets to
   a certain EID in parallel with the Map-Request to obtain a mapping
   when a new flow is established, it creates important security risks
   since it allows attackers to perform identity hijacks.  Although the
   duration of these identity hijacks is limited (except the case of
   rate limitation exhaustion), their impact can be severe.  A first
   option would be to disable gleaning until the security concerns are
   solved.  A second option would be to strictly limit the number of
   packets that can be forwarded via a gleaned entry.  Overall the
   benefits of gleaning, i.e., avoiding the loss of the first packet of
   a flow, seems very small compared to the associated security risks.
   Furthermore, measurements performed in data centers show that today's
   Internet often operate with packet loss ratio of 1 or 2 percentage
   ([Chu]).  These packet loss ratios are probably already orders of
   magnitude larger than the improvement provided by the gleaning
   mechanism.



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   With the increasing deployment of spoofing prevention techniques such
   as [RFC3704] or SAVI [SAVI], it can be expected that attackers will
   become less capable of sending packets with a spoofed source address.
   To prevent packet injection attacks from non-spoofing attackers
   (NSA), ETRs should always verify that the source RLOC of each
   received LISP data encapsulated packet corresponds to one of the
   RLOCs listed in the mappings for the source EID found in the inner
   packet.  An alternative could be to use existing IPSec techniques
   [RFC4301] and when necessary including perhaps [RFC5386] to establish
   an authenticated tunnel between the ITR and the ETR.

   [RFC6830] recommends to rate limit the control messages that are sent
   by an xTR.  This limit is important to deal with denial of service
   attacks.  However, a strict limit, e.g., implemented with a token
   bucket, on all the Map-Request and Map-Reply messages sent by an xTR
   is not sufficient.  An xTR should distinguish between different types
   of control plane packets:

   1.  The Map-Request messages that it sends to refresh expired mapping
       information.

   2.  The Map-Request messages that it sends to obtain mapping
       information because one of the served hosts tried to contact an
       external EID.

   3.  The Map-Request messages that it sends as reachability probes.

   4.  The Map-Reply messages that it sends as response to reachability
       probes.

   5.  The Map-Request messages that it sends to support gleaning.

   These control plane messages are used for different purposes.  Fixing
   a global rate limit for all control plane messages increases the risk
   of Denial of Service attacks if a single type of control plane
   message can exceed the configured limit.  This risk could be
   mitigated by either specifying a rate for each of the five types of
   control plane messages.  Another option could be to define a maximum
   rate for all control plane messages, and prioritize the control plane
   messages according to the list above (with the highest priority for
   message type 1).

   In [RFC6830], there is no mechanism that allows an xTR to verify the
   validity of the content a Map-Reply message that it receives.
   Besides the attacks discussed earlier in the document, a time-shifted
   attack where an attacker is able to modify the content of a Map-Reply
   message but then needs to move off-path could also create redirection
   attacks.  The nonce only allows an xTR to verify that a Map-Reply



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   responds to a previously sent Map-Request message.  To verify the
   validity and integrity of bindings between EID-Prefixes and their
   RLOCS, solutions proposed in [I-D.saucez-lisp-mapping-security] and
   [I-D.ietf-lisp-sec] could be deployed.  Having LISP-SEC and lisp-
   mapping-security in place would prevent all the above-mentioned
   threats.

   Finally, there is also the risk of Denial of Service attack against
   the EID-to-RLOC Cache.  We have discussed these attacks when
   considering external attackers with, e.g., the gleaning mechanism and
   in Section 5.2.  If an ITR has a limited EID-to-RLOC Cache, a
   malicious or compromised host residing in the site that it serves
   could generate packets to random destinations to force the ITR to
   issue a large number of Map-Requests whose answers could fill its
   cache.  Faced with such misbehaving hosts, LISP ITR should be able to
   limit the percent of Map-Requests that it sends for a given source
   EID.

   In order to mitigate flooding attacks it would be worth consider
   developing secure mechanisms to allow an ETR to indicate to an ITR
   that it does not serve a particular EID or block of EIDs.


12.  IANA Considerations

   This document makes no request to IANA.


13.  Security Considerations

   Security considerations are the core of this document and do not need
   to be further discussed in this section.


14.  Acknowledgments

   This document builds upon the draft of Marcelo Bagnulo
   ([I-D.bagnulo-lisp-threat]), where the flooding attack and the
   reference environment were first described.

   The authors would like to thank Vina Ermagan, Darrel Lewis, and Jeff
   Wheeler for their comments.

   This work has been partially supported by the INFSO-ICT-216372
   TRILOGY Project (www.trilogy-project.org).


15.  References



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15.1.  Normative References

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              January 2013.

   [RFC6832]  Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking between Locator/ID Separation Protocol
              (LISP) and Non-LISP Sites", RFC 6832, January 2013.

   [RFC6833]  Fuller, V. and D. Farinacci, "Locator/ID Separation
              Protocol (LISP) Map-Server Interface", RFC 6833,
              January 2013.

   [RFC6834]  Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID
              Separation Protocol (LISP) Map-Versioning", RFC 6834,
              January 2013.

   [RFC6836]  Fuller, V., Farinacci, D., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol Alternative Logical
              Topology (LISP+ALT)", RFC 6836, January 2013.

   [RFC6837]  Lear, E., "NERD: A Not-so-novel Endpoint ID (EID) to
              Routing Locator (RLOC) Database", RFC 6837, January 2013.

15.2.  Informative References

   [Chu]      Jerry Chu, H., "Tuning TCP Parameters for the 21st
              Century",  75th IETF, Stockholm, July 2009,
              <http://tools.ietf.org/wg/savi/>.

   [I-D.bagnulo-lisp-threat]
              Bagnulo, M., "Preliminary LISP Threat Analysis",
              draft-bagnulo-lisp-threat-01 (work in progress),
              July 2007.

   [I-D.ietf-lisp-ddt]
              Fuller, V., Lewis, D., Ermagan, V., and A. Jain, "LISP
              Delegated Database Tree", draft-ietf-lisp-ddt-00 (work in
              progress), October 2012.

   [I-D.ietf-lisp-sec]
              Maino, F., Ermagan, V., Cabellos-Aparicio, A., Saucez, D.,
              and O. Bonaventure, "LISP-Security (LISP-SEC)",
              draft-ietf-lisp-sec-04 (work in progress), October 2012.

   [I-D.ietf-tcpm-tcp-security]
              Gont, F., "Survey of Security Hardening Methods for



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              Transmission Control Protocol (TCP) Implementations",
              draft-ietf-tcpm-tcp-security-03 (work in progress),
              March 2012.

   [I-D.meyer-lisp-cons]
              Brim, S., "LISP-CONS: A Content distribution Overlay
              Network Service for LISP", draft-meyer-lisp-cons-04 (work
              in progress), April 2008.

   [I-D.saucez-lisp-mapping-security]
              Saucez, D. and O. Bonaventure, "Securing LISP Mapping
              replies", draft-saucez-lisp-mapping-security-00 (work in
              progress), February 2011.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC5386]  Williams, N. and M. Richardson, "Better-Than-Nothing
              Security: An Unauthenticated Mode of IPsec", RFC 5386,
              November 2008.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, February 2012.

   [SAVI]     IETF, "Source Address Validation Improvements Working
              Group", <http://tools.ietf.org/wg/savi/>.

   [Saucez09]
              Saucez, D. and L. Iannone, "How to mitigate the effect of
              scans on mapping systems",  Submitted to the Trilogy
              Summer School on Future Internet.


Appendix A.  Document Change Log

   o  Version 04 Posted February 2013.

      *  Clear statement that the document compares threats of public
         LISP deployments with threats in the current Internet
         architecture.

      *  Addition of a severity level discussion at the end of each
         section.





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      *  Addressed comments from D. Lewis' review.

      *  Updated References.

      *  Further editorial polishing.

   o  Version 03 Posted October 2012.

      *  Dropped Reference to RFC 2119 notation because it is not
         actually used in the document.

      *  Deleted future plans section.

      *  Updated References

      *  Deleted/Modified sentences referring to the early status of the
         LISP WG and documents at the time of writing early versions of
         the document.

      *  Further editorial polishing.

      *  Fixed all ID nits.

   o  Version 02 Posted September 2012.

      *  Added a new attack that combines overclaiming and de-
         aggregation (see Section 6.2).

      *  Editorial polishing.

   o  Version 01 Posted February 2012.

      *  Added discussion on LISP-DDT in Section 9.2.

   o  Version 00 Posted July 2011.

      *  Added discussion on LISP-MS in Section 10.

      *  Added discussion on Instance ID in Section 5.4.

      *  Editorial polishing of the whole document.

      *  Added "Change Log" appendix to keep track of main changes.

      *  Renamed "draft-saucez-lisp-security-03.txt.






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Authors' Addresses

   Damien Saucez
   INRIA
   2004 route des Lucioles BP 93
   06902 Sophia Antipolis Cedex
   France

   Email: damien.saucez@inria.fr


   Luigi Iannone
   Telecom ParisTech
   23, Avenue d'Italie, CS 51327
   75214 PARIS Cedex 13
   France

   Email: luigi.iannone@telecom-paristech.fr


   Olivier Bonaventure
   Universite catholique de Louvain
   Place St. Barbe 2
   Louvain la Neuve
   Belgium

   Email: olivier.bonaventure@uclouvain.be
























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