Capabilities and Limitations of an Endpoint-only Security Solution
draft-taddei-smart-cless-introduction-01

Document Type Active Internet-Draft (individual)
Last updated 2019-07-08
Stream (None)
Intended RFC status (None)
Formats plain text pdf html bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
IETF                                                           A. Taddei
Internet-Draft                                                 C. Wueest
Intended status: Informational                                 K. Roundy
Expires: January 9, 2020                            Symantec Corporation
                                                             D. Lazanski
                                                        Last Press Label
                                                           July 08, 2019

   Capabilities and Limitations of an Endpoint-only Security Solution
                draft-taddei-smart-cless-introduction-01

Abstract

   In the context of existing, proposed and newly published protocols,
   this draft RFC is to establish the capabilities and limitations of
   endpoint-only security solutions and explore benefits and
   alternatives to mitigate those limits with the support of real case
   studies.

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 https://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 January 9, 2020.

Copyright Notice

   Copyright (c) 2019 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
   (https://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

Taddei, et al.           Expires January 9, 2020                [Page 1]
Internet-Draft                    CLESS                        July 2019

   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.  Abbreviations . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Disclaimer  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Endpoints: definitions, models and scope  . . . . . . . . . .   6
     5.1.  Internal representation of an endpoint  . . . . . . . . .   7
     5.2.  Endpoints modeled in an end-to-end context  . . . . . . .   8
   6.  Threat Landscape  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Endpoint Security Capabilities  . . . . . . . . . . . . . . .  11
   8.  What would be a perfect endpoint security solution? . . . . .  14
   9.  The defence-in-depth principle  . . . . . . . . . . . . . . .  15
   10. Endpoint Security Limits  . . . . . . . . . . . . . . . . . .  16
     10.1.  No possibility to put an endpoint security add-on on the
            UE . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
       10.1.1.  Not receiving any updates or functioning patches . .  18
       10.1.2.  Mirai IoT bot  . . . . . . . . . . . . . . . . . . .  19
     10.2.  Endpoints may not see the malware on the endpoint  . . .  20
       10.2.1.  LoJax UEFI rootkit . . . . . . . . . . . . . . . . .  20
       10.2.2.  SGX Malware  . . . . . . . . . . . . . . . . . . . .  21
       10.2.3.  AMT Takeover . . . . . . . . . . . . . . . . . . . .  21
       10.2.4.  AMT case study (anonymised)  . . . . . . . . . . . .  22
       10.2.5.  Users bypass the endpoint security . . . . . . . . .  23
     10.3.  Endpoints may miss information leakage attacks . . . . .  23
       10.3.1.  Meltdown/Specter . . . . . . . . . . . . . . . . . .  23
       10.3.2.  Network daemon exploits  . . . . . . . . . . . . . .  23
       10.3.3.  SQL injection attacks  . . . . . . . . . . . . . . .  24
       10.3.4.  Low and slow data exfiltration . . . . . . . . . . .  24
     10.4.  Suboptimality and gray areas . . . . . . . . . . . . . .  25
       10.4.1.  Stolen credentials . . . . . . . . . . . . . . . . .  25
       10.4.2.  Zero Day Vulnerability . . . . . . . . . . . . . . .  26
       10.4.3.  Port scan over the network . . . . . . . . . . . . .  26
       10.4.4.  DDoS attacks . . . . . . . . . . . . . . . . . . . .  27
   11. Learnings from production data  . . . . . . . . . . . . . . .  28
     11.1.  Endpoint only incidents  . . . . . . . . . . . . . . . .  29
     11.2.  Security incidents detected primarily by network
            security products  . . . . . . . . . . . . . . . . . . .  30
       11.2.1.  Unauthorized external vulnerability scans  . . . . .  30
       11.2.2.  Unauthorized internal vulnerability scans  . . . . .  31
       11.2.3.  Malware downloads resulting in exposed endpoints . .  31
       11.2.4.  Exploit kit infections . . . . . . . . . . . . . . .  31
       11.2.5.  Attacks against servers  . . . . . . . . . . . . . .  32
   12. Regulatory Considerations . . . . . . . . . . . . . . . . . .  33

Taddei, et al.           Expires January 9, 2020                [Page 2]
Internet-Draft                    CLESS                        July 2019

     12.1.  IoT Security . . . . . . . . . . . . . . . . . . . . . .  33
     12.2.  Network infrastructure . . . . . . . . . . . . . . . . .  34
     12.3.  Auditing and Assessment  . . . . . . . . . . . . . . . .  34
     12.4.  Privacy Considerations . . . . . . . . . . . . . . . . .  35
   13. Human Rights Considerations . . . . . . . . . . . . . . . . .  35
   14. Security Considerations . . . . . . . . . . . . . . . . . . .  35
   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35
   16. Informative References  . . . . . . . . . . . . . . . . . . .  35
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  40
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction

   This Internet Draft aims to be a reference to the designers of
   protocols on the capabilities and limitations of security solutions
   on endpoint devices against malware and other attacks.  As security
   is entering a new phase in the arms race between attackers and
   defenders, with many technical, economic and regulatory changes, and
   with a significant increase in major data breaches, it is a good
   moment to propose a systematic review and update on what is an old
   and constantly evolving problem: endpoint security.

   With the above context in mind this document will focus on the
   capabilities and limitations of an endpoint-only security solution.

   We want to explore a number of questions:

   o  What endpoint models do we have?

   o  What is the threat landscape under consideration?

   o  Can we differentiate security and privacy threats?

   o  What are common endpoint security capabilities?

   o  What would be an ideal endpoint security solution?

   o  What are the limits to endpoint security?

   o  What is real production data telling us?

   o  What can defence-in-depth help us with?

   o  What are the economic considerations?

   o  What are the regulatory considerations and constraints?

   o  What are the human rights considerations?

Taddei, et al.           Expires January 9, 2020                [Page 3]
Internet-Draft                    CLESS                        July 2019

   Our goal with this review is to describe the benefits and limitations
   of endpoint security in the real world, rather than in the abstract.
   We aim to highlight security limitations that cannot be addressed by
   endpoint solutions and to suggest how these may be mitigated with the
   concept of a defence-in-depth approach, in order to increase the
   resilience against attacks and data breaches.

2.  Abbreviations

   In this section we provide main abbreviations expansions

   ABAC  Attribute Based Access Control

   AI Artificial Intelligence

   AMT  Active Management Technology

   C&C  Command and Control

   CFI  Control Flow Integrity

   CFG  Control Flow Guard

   DDoS  Distributed Denial of Service

   DEP  Data Execution Prevention

   DGA  Domain Generating Algorithms

   DLP  Data Loss Prevention

   DMARC  Domain-based Message Authentication, Reporting and Conformance

   DoS  Denial of Service

   EE Execution Environment

   EDR  Endpoint Detection and Response

   EPP  Endpoint Protection Platform

   FP False Positive

   HIPS  Host Intrusion Prevention System

   ICD  Integrated Cyber Defence

   ICMP  Internet Control Message Protocol

Taddei, et al.           Expires January 9, 2020                [Page 4]
Internet-Draft                    CLESS                        July 2019

   IDS  Intrusion Detection System

   IoT  Internet of Things

   IPS  Intrusion Prevention System

   ML Machine Learning

   MSS  Managed Security Services

   MSSP  Managed Security Services Provider

   NIST  National Institute of Standards and Technology

   NX No Execute Bit

   P2P  Peer to Peer

   RAP  Reuse Attack Protector

   RBAC  Role Based Access Control

   RDP  Remote Desktop Protocol

   ROP  Return Oriented Programming

   SANS  System Administration, Networking, and Security

   SGX  Software Guard eXtensions

   SSH  Secure SHell

   UE User Equipment

   UEFI  Unified Extensible Firmware Interface

   UX User Experience

   VM Virtual Machine

   XSS  Cross Site Scripting

3.  Definitions

   In this section we provide definitions that are marked

   o  (L) Local to this document

Taddei, et al.           Expires January 9, 2020                [Page 5]
Internet-Draft                    CLESS                        July 2019

   o  (G REFERENCE) Global and then will be preceded by a reference

   DoS (L)  Literally a Denial of Service.  Not to be confused with a
      Network DoS or DDoS.

   Endpoint security capabilities (L)  How to protect the endpoint with
      three different aspects of protection:

   o  Prevention - The attack doesn't succeed by intrinsic or explicit
      security capabilities.

   o  Detection - The attack is happening or has happened and is
      recorded and/or signalled to another component for action.

   o  Mitigation - Once detected, the attack can be halted or its
      effects can at least be reduced or reversed.

   System (L)  A system is a heterogeneous set of any IT capabilities
      including hardware, software, endpoints (including IoT), networks,
      data centers and platforms with no assumptions on deployment form
      factor (physical, virtual, microservices), deployment scenario,
      geographic distribution, or dispersion.

   User Equipment (G ITU-T H.360)  Equipment under the control of an End
      User

4.  Disclaimer

   This document is a first draft and is incomplete on purpose.  Indeed
   there are several areas where there are different ways to develop
   this draft and the authors are seeking for feedback and extended
   collaboration.  This is to be noted too, that this is the first draft
   RFC for the authors and contributors, so, coaching and help will be
   appreciated.  Overall, 'a bon entendeur, salut'.

   Comments are solicited and should be addressed to the authors.

5.  Endpoints: definitions, models and scope

   Endpoints are the origin and destination for a communication between
   parties.  This encompasses User Equipment (UE) and the Host at the
   other end of the communication.  Whilst it is recognized that these
   two ends of the communication may represent a vast amount of diverse
   endpoints, this document will set here a requirement for a uniform
   way to describe the endpoints in order to work from an equally
   uniform representation of what is called the Attack Surface.  In the
   same spirit as the IETF TEEP Working Group generalized its work, see
   [TEEP], this document will rely on another document identified as

Taddei, et al.           Expires January 9, 2020                [Page 6]
Internet-Draft                    CLESS                        July 2019

   [I-D.draft-mcfadden-smart-endpoint-taxonomy-for-cless-00] in order to
   represent the taxonomy of endpoints.

   For example:

   o  The following would be considered as UEs: a smartphone, a smart
      device, any IoT device, a laptop, a desktop, a workstation, etc.

   o  Hosts represent too, physical servers, virtual servers/machines,
      etc.

   We require a framework in order to define and model the endpoint
   itself and the position of the endpoint in the network.  In this
   initial analysis we focus on endpoints that are User Equipment (UE)
   rather than on hosts.  In the future, with the help of
   [I-D.draft-mcfadden-smart-endpoint-taxonomy-for-cless-00] we hope to
   balance and unify the model.

   In addition, we need two models for the endpoint, internally and in
   an end-to-end context within the network.  With this approach we
   expect both models to help us cover all the attack surface and the
   threat landscape and therefore help us list the capabilities and
   limitations for endpoint security.

   Indeed, this will help us understand point attacks versus composite
   attacks within context, and, accordingly, understand holistically the
   capabilities and the limitations of endpoint security.  For example
   to differentiate when only an application on the end point is
   affected.

5.1.  Internal representation of an endpoint

   This section interfaces here with
   [I-D.draft-mcfadden-smart-endpoint-taxonomy-for-cless-00] which
   starts from the below internal representation of an endpoint which
   could be generalized by the simple diagram below:

   +----------------------------+
   | Application                |
   +----------------------------+
   | OS / Execution Environment |
   +----------------------------+
   | Hardware                   |
   +----------------------------+

Taddei, et al.           Expires January 9, 2020                [Page 7]
Internet-Draft                    CLESS                        July 2019

   Today there are many combinations of Hardware, OS/EE pairing and
   Application layers, offering the user a vast set of features with a
   wide spectrum of capabilities.

   Furthermore we can consider that an application running on a UE or a
   host is an endpoint too, so we have multiple ways to read the above
   diagram.

   In essence we want to consider here endpoints including those which
   have a variance in electrical power, computational power, memory,
   disk, network interfaces, size, ownership, connectics, etc. and
   therefore why we rely on
   [I-D.draft-mcfadden-smart-endpoint-taxonomy-for-cless-00].

5.2.  Endpoints modeled in an end-to-end context

   A representation of endpoints in an end-to-end context could look
   like the following diagram:

   +-------+           +---------------------+---------+
   | Human | <- (1) -> | Digital Persona | Application | <- (2) ->
   +-------+           +-----------+-------------------+
                       | User Equipment                |
                       +-------------------------------+

                       +----------------+           +----------------+
             <- (2) -> | Network        | <- (3) -> | Platform/Hosts |
                       | Infrastructure |           +----------------+
                       +----------------+

   1.  Humans have a user experience (UX) with the UE, starting with an
       explicit or implicit Digital Persona, engaging with an
       application

   2.  The application will have sessions through a large Network
       Infrastructure where we do not assume anything of the
       infrastructure (could be landlines, mobile networks, satellites,
       etc.) and those sessions reach

   3.  a Platform consisting of many Hosts either physical or virtual
       and it ensures a large part of the end-to-end user experience.

Taddei, et al.           Expires January 9, 2020                [Page 8]
Internet-Draft                    CLESS                        July 2019

   In this end-to-end model we see that many other systems may have
   interactions with the UE: the human, the UX, the digital persona, the
   sessions, the intermediate network infrastructure, and the hosts and
   application at the destination.

   If we now look at security aspects of the above models, the threat
   landscape is very large and the attack surface will cover all the
   components and interactions at any level.

6.  Threat Landscape

   (Editor's note: this section will require a significant amount of
   future development.)

   Given the vast number of combinations that the above generic modeling
   offers us, defining a threat landscape should be done carefully and
   will require a systematic methodology.

   Therefore this entire section will be developed through future
   iterations of the document, in this initial version we will start
   structuring an approach and then adjust this based on feedback.

   There is no doubt that we want to cover typical known attacks such
   as:

   o  Malware (Trojans, viruses, backdoors, bots, etc.)

   o  Adware and spyware

   o  Exploits

   o  Phishing

   o  Script based attacks

   o  Ransomware, local Denial of Service (DoS) attacks

   o  Denial of Service (DoS) attacks

   o  Malicious removable storage devices (USB)

   o  In memory attacks

   o  Rootkits and firmware attacks

   o  Scams and online fraud

   o  System abuse (staging/proxying)

Taddei, et al.           Expires January 9, 2020                [Page 9]
Internet-Draft                    CLESS                        July 2019

   o  etc.

   To illustrate the difficulty to define a good threat landscape, when
   it comes to cryptojacking and coinmining that were on the rise, in
   which category do they fall: malware?  DoS? system abuse? or a
   category on its own?

   This is why we wanted to conduct a thorough gap analysis using
   existing definitions and frameworks, but we couldn't find an existing
   comprehensive and recognized taxonomy dedicated to the threat
   landscape on endpoints.  We found however different models in this
   field, and have considered two.  We are open to further suggestions.

   Indeed both of the analysed frameworks contain threat landscape
   descriptions:

   o  MITRE Common Attack Pattern Enumeration Classification (CAPEC).
      See [CAPEC].

   o  MITRE ATT&CK.  See [ATTACK].

   These offer us interesting ways to assess the threat landscape:

   o  CAPEC offers a hierarchical view of attack patterns by domains
      which can match some aspects of both of our above models, but we
      will need to identify those attacks that fit exactly in our scope.

   o  ATT&CK offers a very straightforward categorized knowledge base of
      attacks, but it concentrates on the entreprise attack chain, so we
      will need to do some work to extract what we need.

   We recognise however that these frameworks do not address all of the
   threats that can affect the security of a system, for example they do
   not cover; routing hijacking, flooding, selective blocking,
   unauthorised modification of data sent to an endpoint, etc.  Further
   work to define categories of threats is therefore required.

   As a further example, phishing should be included as an attack, but
   whilst this is indeed an attack that will materialize on a device
   through an application (email, webmail, etc.), the real target of
   this attack is not the device, but the human behind the digital
   persona.

   Having a methodology of assessment is necessary here, because it will
   help decide what is in scope vs. out of scope.

   We are aware that once a method and the categories are fully defined
   in this section, it will force a review of all the following sections

Taddei, et al.           Expires January 9, 2020               [Page 10]
Internet-Draft                    CLESS                        July 2019

   in the document.  Whilst remapping will be necessary, it should not
   drastically change the draft.

7.  Endpoint Security Capabilities

   In this section we try to define some endpoint security capabilities
   (Editor's note: this section will require future development.)

   In this version of the document we will start by developing a
   framework to categorize and position endpoint security capabilities
   with the goal of defining what an ideal endpoint security capability
   would look like.

   By endpoint security capabilities we mean how to protect the endpoint
   against attacks.  Protection has many meanings, we want to
   distinguish three different aspects of protection:

   o  Prevention - The attack doesn't succeed by intrinsic or explicit
      security capabilities.

   o  Detection - The attack is happening or has happened and is
      recorded and/or signalled to another component for action.

   o  Mitigation - Once detected, the attack can be halted or its
      effects can at least be reduced or reversed.

   For example, prevention methods include keeping the software updated
   and patching vulnerabilities, implementing measures to authenticate
   the provenance of incoming data to stop the delivery of malicious
   content, or choosing strong passwords.  Detection methods include
   inspecting logs or network traffic.  Mitigation could include
   deploying backups to recover from an attack with minimal disruption.

   Our intention however is not just to consider each endpoint security
   capability separately, but also the overall endpoint security
   holistically with all its interdependencies.  Indeed, we defined a
   simple endpoint, but each layer may or may not have a certain
   spectrum of intrinsic capabilities and there may be multiple ways to
   provide add-on and third-party endpoint security capabilities,
   allowing complex interactions between all of these components.

   We define two different aspects of endpoint security capabilities and
   their subdivisions as:

   o  (A) Intrinsic security capability can be built-into each of the
      endpoint model layers

      *  (1) Hardware

Taddei, et al.           Expires January 9, 2020               [Page 11]
Internet-Draft                    CLESS                        July 2019

      *  (2) OS/EE

      *  (3) Application

   o  (B) Add-on security capability can be

      *  (4) a component of the hardware

      *  (5) a component of the OS/EE

      *  (6) an application by itself

   In (A) we relate to a 'security by design' intention of the
   developers and they will intrinsically offer a security model and
   security capabilities as part of their design.  A typical example of
   this is the authorization model.

   In (B) a 3rd party is offering an additional security component which
   was not necessarily considered when the Hardware, OS/EE or
   Application were designed.

   In the future we will review all the main categories of security
   capabilities that are known to date and assess security capability
   enablers like Artificial Intelligence (AI) and Machine Learning (ML).
   For each category we will try to give a review on how effective the
   capability is in securing the system.

   With regard to (6), there are many available options for add-on
   security capabilities offered by third-parties as applications on a
   commercial or open-source basis.  Gartner (see [GARTNERREPORT])
   highlights the evolution of endpoint security towards two directions
   as shown in [EPPEDR], [EPPSECURITY], [EPPGUIDE].

   o  Endpoint Protection Platform (EPP) as an integrated security
      solution designed to detect and block threats at the device level.

   o  Endpoint Detection and Response (EDR) as a combination of next
      generation tools to provide anomaly detection and alerting,
      forensic analysis and endpoint remediation capabilities.

   Among the security capabilities that we list, the endpoint can
   perform the following:

   o  Intrinsic

      *  Software updates / patching

      *  Access Control (RBAC, ABAC, etc.)

Taddei, et al.           Expires January 9, 2020               [Page 12]
Internet-Draft                    CLESS                        July 2019

      *  Authentication

      *  Authorization

      *  Detailed event logging

   o  Execution protection

      *  Exploit mitigation (file/memory)

      *  Tamper protection

      *  Whitelisting filter by signatures, signed code or other means

      *  System hardening and lockdown (HIPS, trusted boot, etc.)

   o  Malware protection

      *  Scanning - on access/on write/scheduled/quick scan (file/
         memory)

      *  Reputation-based blocking on files or by ML

      *  Behavior-based detection - (heuristic based/ML)

      *  Rootkit and firmware detection

      *  Threat intelligence based detection (cloud-based/on premise)

      *  Static detection - generic, by emulation, by ML, by signature

   o  Attack/Exploit/Application Protection

      *  Application protection (browser, messaging clients, social
         media, etc.)

         +  Disinformation Protection (anti-phishing, fake news, anti-
            spam, etc.)

         +  Detection of unintended link location (URL blocklist, etc.)

         +  Memory exploit mitigation, e.g. browsers

      *  Network Protection (local firewall, IDS, IPS and local proxy)
         inbound and outbound

      *  Detection of network manipulation (ARP, DNS, etc.)

Taddei, et al.           Expires January 9, 2020               [Page 13]
Internet-Draft                    CLESS                        July 2019

      *  Data Loss Prevention and exfiltration detection (incl. covert
         channels)

8.  What would be a perfect endpoint security solution?

   With all the above knowledge, let's consider what we could expect
   from a perfect endpoint security 'system'.  It would:

   o  find instantly accurate reputation for any file before it gets
      executed and block it if needed.

   o  monitor any behavior on the endpoint, including inbound and
      outbound network traffic, learn and identify normal behavior and
      detect and block malicious actions, even if the attack is misusing
      legitimate clean system tools or hiding with a rootkit.

   o  patch instantly across all devices/systems/OSes, including virtual
      patching, meaning you can patch or shield an application even
      before an official patch is released.

   o  exploit protection methods for all processes where applicable,
      e.g. no execute bit (NX), data execution prevention (DEP), address
      space layout randomization (ASLR), Control Flow Integrity Guard
      (CFI/CFG), stack canaries, shadow stack, reuse attack protection
      (RAP), etc. all of which are methods, which make it very difficult
      to successfully run any exploit, even for zero day
      vulnerabilities.

   o  detect attempts to re-route data to addresses other than those
      which the user intended, e.g. detect incorrectly served DNS
      entries, TLS connections to sites with invalid certificates, data
      that is being proxied without explicit user consent, etc.

   o  have an emulator/sandbox/micro virtualization to execute code and
      analyse the outcome and perform a roll back of all actions if
      needed, e.g. for ransomware.

   o  allow the endpoint to communicate with the other endpoints in the
      local network and globally, to learn from 'the crowd' and
      dynamically update rules based on its findings.

   o  be in constant sync with all other endpoints deployed on a network
      and other security solutions, run on any OS, with no delay
      (including offline modes and on legacy systems).

   o  run from the OS/EE when possible.

Taddei, et al.           Expires January 9, 2020               [Page 14]
Internet-Draft                    CLESS                        July 2019

   o  run as one of the first process on the OS/EE and protect itself
      from any form of unwanted tampering.

   o  offers a reliable logging that can't be tampered with, even in the
      event of system compromise.

   o  receive updates instantly from a trusted central entity.

9.  The defence-in-depth principle

   In this section we give a high level view of what we mean by
   'defence-in-depth'.

   Whilst endpoint security systems have good capabilities, sometimes it
   is debatable and perhaps suboptimal to let the endpoint run the
   capability alone or at all.  It is generally considered good security
   practice to adopt a defence-in-depth approach (see [USCERT]).  The
   Open Web Application Security Project group (OWASP) describes the
   concept as follows: "The principle of defense-in-depth is that
   layered security mechanisms increase security of the system as a
   whole.  If an attack causes one security mechanism to fail, other
   mechanisms may still provide the necessary security to protect the
   system." (see [OWASP])

   Indeed there are many other constituencies as per our end-to-end
   model that can participate in the defence process: The network, the
   infrastructure itself, the platform, the human, the user experience
   and in a hybrid of an on premise and cloud approach, an Integrated
   Cyber Defence (ICD) of the entire chain.

   The simple idea behind the concept is that "every little helps".  If
   the endpoint is not 100% secure itself, the detection chance can
   increase with additional security capabilities from other entities.
   We acknowledge that there are some case where adding an additional
   component to the system may degrade the overall security level by
   introducing new weaknesses.

   There are various reference article in the industry highlighting
   limitations of endpoint only solutions.  For example this quote here,
   which talks about multi-tier solutions: "There are limitations with
   any endpoint protection solution, however, that can limit protection
   to only the client layer.  There is also a need for security above
   the client layer, as endpoint protection products cannot intercept
   traffic.  Vendors will often sell a multi-tiered solution that
   enables a network appliance to assist the endpoint protection client
   by intercepting traffic between the attacker and the infected client.
   Vendors will also sell solutions that monitor and intercept traffic
   on internal or external network segments to protect the enterprise

Taddei, et al.           Expires January 9, 2020               [Page 15]
Internet-Draft                    CLESS                        July 2019

   from these threats.  A prime example of the limitations of endpoint
   protection software is infection via a phishing attack."  [ADAPTURE].

   Some sources point out that even the best solution might not get
   deployed in the optimal way in a real world scenario as the
   environment can be very complex: "While endpoint security has
   improved significantly with the introduction of application
   whitelisting and other technologies, our systems and devices are
   simply too diverse and too interconnected to ensure that host
   security can be deployed 100% ubiquitously and 100% effectively."
   [NETTODAY]

   On these grounds it is considered a good idea to follow a layered
   approach when it comes to security.  "In today's complex threat
   environment, companies need to adopt a comprehensive, layered
   approach to security, which is a challenging task in such as rapidly
   evolving, crowded market."  [HSTODAY]

   It is important to comprehend the capabilities of endpoint security
   solutions in this overall picture of the connected environment, which
   includes other systems, networks and various protocols that are used
   to interact with these entities.  Understanding possible shortcomings
   from single layered solutions can help counterbalance such weaknesses
   in the architectural concept or the protocol design.

   In order to quantify any potential benefits or limitations of the
   various layered scenarios in regards to security a solid data set is
   needed.  This section requires statistics about proportions of
   attacks that go undetected in various cases.  We propose analysing
   data for the following four cases:

   o  There is no security solution

   o  Security is only on the endpoint

   o  Security is only on the network

   o  Security is on both the endpoint and the network

   However reconciling various statistics requires a lot of caution and
   time, a methodology and consistent classification to avoid any
   misinterpretation.

10.  Endpoint Security Limits

   The previous section defines an ideal endpoint security 'system',
   however, from the real world, the expectation of what we can get from

Taddei, et al.           Expires January 9, 2020               [Page 16]
Internet-Draft                    CLESS                        July 2019

   an endpoint security solution will look more along the following
   lines:

   o  may not be able to run at full capacity due to computational power
      limits, battery life, performance, or policies (such as BYOD
      restrictions in enterprise networks), etc.

   o  may not be able to run at full capacity as it slows down
      performance too much.

   o  will miss some of the malware or attacks, regardless of detection
      method used, like signatures, heuristics, machine learning (ML),
      artificial intelligence (AI), etc.

   o  have some level of False Positives (FP).

   o  not monitoring or logging all activities on the system, e.g. due
      to constraints of disk space or when a clean windows tool is being
      triggered to do something malicious but the activity is not
      logged.  Such activity can be logged, but a decision needs to be
      made if it's clean or not.

   o  have its own vulnerabilities or simple instabilities that could be
      used to compromise the system.

   o  be tampered with by the user, e.g. disabled or reconfigured.

   o  be tampered with by the attacker, e.g. exceptions added or log
      files wiped.

   In the section below we review a number of these limitations through
   real examples, step by step.  Some limitations are absolute, and some
   limitations result in a grey area or suboptimality for the solution.

10.1.  No possibility to put an endpoint security add-on on the UE

   UEs will vary a lot; by 2022, an estimated 29 billion devices will be
   connected, with 18 billion of them related to IoT [ERICSSON].  Many
   IoT products lack the capacity to install any endpoint security
   capabilities, are unable to update the software, and it is not
   possible to force the UE provider to improve or even offer an
   intrinsic security capability.

   We acknowledge that the numbers do vary significantly depending on
   the source, for example:

   o  [STATISTA1] is showing the current trajectory of IoT devices from
      25B to date to 40+B in 2022 and 75B in 2025.

Taddei, et al.           Expires January 9, 2020               [Page 17]
Internet-Draft                    CLESS                        July 2019

   o  [ERICSSON] is more conservative and might requires an update, but
      it was reaching 29B devices in 2022, with a nice breakdown between
      device types and connectivity.

   o  [STATISTA2] is showing a breakdown by verticals and is even more
      conservative than both of the above.

   o  [ENISA] it refers to a [GARTNERIOT] report from 2017 which sets a
      trajectory to 20B devices by 2020.

   In IoT we find UEs such as medical devices which are limited by
   regulation, welding robots that can't be slowed down, smart light
   bulbs which are limited by the processing power, etc.  There are many
   factors influencing whether endpoint security can be added to a UE:

   o  The UE is simply not powerful enough or the performance hit is too
      high.

   o  Adding your own security will breach the warranty or will
      invalidate a certification or a regulation (breach of validity).

   o  The UE needs to run in real-time and any delay introduced by a
      security process might break the process.

   o  Some UEs are simply locked by design and the manufacturer does not
      provide a security solution (e.g. smart TV, fitness tracker or
      personal artificial assistants) see [CANDID1], [CANDID2].

   In the future, a possible research problem would be to find hard data
   on the exact proportion of IoT devices that are unable to run any
   endpoint security add-on or that have no intrinsic security built-in.

   The other hidden dimension here is the economical aspect.  Many
   manufacturer are reluctant to invest in IoT device security, because
   it can significantly increases the cost of their solution and there
   is the perception that they will lose market shares, as customers are
   not prepared to pay the extra cost for added security.

10.1.1.  Not receiving any updates or functioning patches

   The endpoint security system may lack a built-in capability to be
   patched or it may be connected to a network that prevents the process
   of downloading updates automatically.  For example stand-alone
   medical systems or industrial systems in isolated network segments
   often do not have a communication channel to the Internet.

   Even if security updates are received, they typically will only be
   periodically updated; hence there will be a window of opportunity for

Taddei, et al.           Expires January 9, 2020               [Page 18]
Internet-Draft                    CLESS                        July 2019

   an attacker, between the time the attack is first used, and the time
   the attack is discovered/patched and the patch is deployed.

   In addition updates and patches may themselves be malicious by
   mistake, or on purpose if not properly authenticated, or if the
   source of the updates has malicious intent.  This could be part of a
   software update supply chain attack or an elaborate attacker breaking
   the update process, as for example seen with the Flamer group (see
   [FLAMER]).

   A recent survey found that fewer than 10% of consumer IoT companies
   follow vulnerability disclosure guidelines at all, which is regarded
   as a basic first step in patching vulnerabilities (see
   [IOTPATCHING]).  This indicates that many IoT devices do not have a
   defined update process or may not even create patches for most of the
   vulnerabilities.

   Furthermore some endpoints system may reach the end of their support
   period and therefore no longer receive any updates for the OS/EE or
   the security solution due to missing licenses.  However the systems
   may remain in use and become increasingly vulnerable as time goes on
   and new attacks are discovered.

10.1.2.  Mirai IoT bot

Taddei, et al.           Expires January 9, 2020               [Page 19]
Internet-Draft                    CLESS                        July 2019

   +-------------+-----------------------------------------------------+
   | Description | A Mirai bot infecting various IoT devices through   |
   |             | weak passwords over Telnet port TCP 23 and by using |
   |             | various vulnerabilities, for example the SonicWall  |
   |             | GMS XML-RPC Remote Code Execution Vulnerability     |
   |             | (CVE-2018-9866) on TCP port 21009. Once a device is |
   |             | compromised it will scan for further victims and    |
   |             | then start a DoS attack.                            |
   +-------------+-----------------------------------------------------+
   | Simplified  | Compromised device scans network for multiple open  |
   | attack      | ports, attempts infection through weak password and |
   | process     | exploits, downloads more payload, starts DoS        |
   |             | attack.                                             |
   |             |                                                     |
   | UE          | No security tool present on majority of IoT         |
   |             | devices, hence no detection possible. If a          |
   |             | rudimentary security solution with limited          |
   |             | capabilities such as outgoing firewall is present   |
   |             | on the IoT device e.g. router, then it might be     |
   |             | able to detect the outbound DoS attack and slow it  |
   |             | down.                                               |
   |             |                                                     |
   | References  | [MIRAI1][MIRAI2]                                    |
   +-------------+-----------------------------------------------------+

10.2.  Endpoints may not see the malware on the endpoint

10.2.1.  LoJax UEFI rootkit

Taddei, et al.           Expires January 9, 2020               [Page 20]
Internet-Draft                    CLESS                        July 2019

   +-------------+-----------------------------------------------------+
   | Description | A device compromised with the LoJax UEFI rootkit,   |
   |             | which is active before the OS/EE is started, hence  |
   |             | before the endpoint security is active. It can pass |
   |             | back a clean 'image' when the security solution     |
   |             | tries to scan the UEFI. Infection can either happen |
   |             | offline with physical access or through a dropper   |
   |             | malware from the OS/EE.                             |
   +-------------+-----------------------------------------------------+
   | UE          | A perfect endpoint security could potentially       |
   |             | detect the installation process if it is done from  |
   |             | the OS/EE and not with physical modification or in  |
   |             | the factory. Once the device is compromised the     |
   |             | endpoint security solution can neither detect nor   |
   |             | remove the rootkit. The endpoint solution may       |
   |             | detect any of the exhibited behaviour, for example  |
   |             | if the rootkit drops another malware onto the OS/EE |
   |             | at a later stage.                                   |
   |             |                                                     |
   | Reference   | [LOJAX]                                             |
   +-------------+-----------------------------------------------------+

10.2.2.  SGX Malware

   +-------------+-----------------------------------------------------+
   | Description | Malware can hide in the Intel Software Guard        |
   |             | eXtensions (SGX) enclave chip feature. This is a    |
   |             | hardware-isolated section of the CPU's processing   |
   |             | memory. Code running inside the SGX can use return- |
   |             | oriented programming (ROP) to perform malicious     |
   |             | actions.                                            |
   +-------------+-----------------------------------------------------+
   | UE          | Since the SGX feature is by design out of reach for |
   |             | the OS/EE, an endpoint security solution can        |
   |             | neither detect nor remove any injected malware. A   |
   |             | perfect endpoint security solution could            |
   |             | potentially detect the installation process if it   |
   |             | is done from the OS/EE and not with physical        |
   |             | modification or in the factory.                     |
   |             |                                                     |
   | References  | [SGX1] [SGX2]                                       |
   +-------------+-----------------------------------------------------+

10.2.3.  AMT Takeover

Taddei, et al.           Expires January 9, 2020               [Page 21]
Internet-Draft                    CLESS                        July 2019

   +-------------+-----------------------------------------------------+
   | Description | A targeted attack group can remotely execute code   |
   |             | on a system through the Intel AMT (Active           |
   |             | Management Technology) vulnerability                |
   |             | (CVE-2017-5689) over TCP ports 16992/16993. This    |
   |             | provides full access to the computer, including     |
   |             | remote keyboard and monitor access. The attacker    |
   |             | can install malware, modify the system or steal     |
   |             | information.                                        |
   +-------------+-----------------------------------------------------+
   | UE          | The AMT is accessible even if the PC is turned off. |
   |             | Therefore any endpoint security software installed  |
   |             | on the OS, would not be able to see this traffic    |
   |             | and therefore also not able to detect it.           |
   |             |                                                     |
   | References  | [AMT1], [AMT2]                                      |
   +-------------+-----------------------------------------------------+

10.2.4.  AMT case study (anonymised)

   An enterprise has a data center containing very sensitive data.
   Their workstations use a certain Intel chipset which integrates the
   AMT feature for remote computer maintenance.  AMT is an interface for
   hardware management of the workstations, including transmission of
   screen content and keyboard and mouse input for remote maintenance.
   Communication with the management workstation is implemented by AMT
   through the network interface card (NIC) on the motherboard.  The
   network packets generated in this way are invisible both to the main
   processor and thus to the OS running on the workstation.  In autumn
   of 2015, it became known that some AMT-enabled computers had a flaw
   that allowed AMT's remote maintenance component to be activated and
   configured by attackers.  This also worked when the workstations were
   switched off.  The leakage of data through this vulnerability is
   elusive and difficult to detect.  The identified threat situation led
   the organization to a new requirement implementing a method that can
   reliably detect this and similar vulnerabilities.  In particular, the
   detection of rootkits and manipulated firmware, and this includes
   also (UEFI) BIOS - has also been a focus of their attention.

   The method used as a solution, compares the desired data packets
   generated by a client operating system - the user, with the data
   packets received on the switch port.  If more data has been received
   on the switch port than was been sent by the operating system - the
   user, there is a strong possibility that something bad is happening -
   like for example an infection via modified firmware or by rootkit.

Taddei, et al.           Expires January 9, 2020               [Page 22]
Internet-Draft                    CLESS                        July 2019

10.2.5.  Users bypass the endpoint security

   +-------------+-----------------------------------------------------+
   | Description | Endpoint security systems should not interfere with |
   |             | the normal operation of the endpoint to the extent  |
   |             | that users become frustrated and want to disable    |
   |             | them or configure them to disable a significant     |
   |             | fraction of important security capabilities.        |
   +-------------+-----------------------------------------------------+
   | UE          | Add-on endpoint security is now bypassed or         |
   |             | disabled by the user. Unless the endpoint is under  |
   |             | monitored management or can prevent a user from     |
   |             | modifying the configuration, then this is shutting  |
   |             | down a significant fraction of the security         |
   |             | capabilities.                                       |
   |             |                                                     |
   | References  | [NINESIGNS]                                         |
   +-------------+-----------------------------------------------------+

10.3.  Endpoints may miss information leakage attacks

   Another aspect that endpoint security has issues in detecting are
   information disclosure or leakage attacks, especially on shared
   virtual/physical systems.

10.3.1.  Meltdown/Specter

   The Meltdown/Specter vulnerabilities and all its variants may allow
   reading of physical memory belonging to another virtual machine (VM)
   on the same physical system.  This could reveal passwords,
   credentials, certificates etc.  The trick is that an attacker can
   spin up his own VM on the same physical hardware.  As this VM is
   controlled by the attacker, they will ensure that there is no
   endpoint security that detects the Meltdown exploit code when run.
   It is very difficult for the attacked VM to detect the memory read-
   outs.  For know CPU vulnerabilities there are software patches
   available than can be applied.  If it is an external service
   provider, it might not be in the power of the user to patch the
   physical system or to determine if this has been done by the
   provider.

10.3.2.  Network daemon exploits

   Other attack types, which leak memory data from a vulnerable web
   server, are quite difficult to detect for an endpoint security.  For
   example the Heartbleed bug allows anyone on the Internet to read the
   memory of the systems protected by the vulnerable versions of the
   OpenSSL software.  This could lead to credentials or keys being

Taddei, et al.           Expires January 9, 2020               [Page 23]
Internet-Draft                    CLESS                        July 2019

   exposed.  An endpoint solution needs to either patch the vulnerable
   application or monitor it for any signs of exploitation or data
   leakage and prevent the data from being exfiltrated.

10.3.3.  SQL injection attacks

   A SQL injection attack is an example of an attack that exploits the
   backend logic of an application.  Typically this is a web application
   with access to a database.  By encoding specific command characters
   into the query string, additional SQL commands can be triggered.  A
   successful attack can lead to the content of the whole database being
   exposed to the attacker.  There are other similar attacks that can be
   grouped together for the purpose of this task, such as command
   injection or cross site scripting (XSS).  Although they are different
   attacks, they all at their core fail at input filtering and
   validation, leading to unwanted actions being performed.

   Applications that are vulnerable to SQL injections are very common
   and are not restricted to web applications.  An endpoint solution
   needs to monitor all data entered into possible vulnerable
   applications.  This should include data received from the network.  A
   generic pattern matching for standard SQL injection attack strings
   can be applied to potentially block some of the attacks.  In order to
   block all types of SQL injection attacks the endpoint solution should
   have some knowledge about the logic of the monitored application,
   which helps to determine how normal requests differ from attacks.
   Applications can be analysed at source code level for potential
   weaknesses, but dynamically patching is very difficult.  See [SQL]

10.3.4.  Low and slow data exfiltration

   An endpoint security solution can detect low and slow data
   exfiltration, for example when interesting data sources are tracked
   and access to them is monitored.  If the data source is not on the
   endpoint itself, e.g. a database in the network, then the received
   data needs to be tagged and its further use needs to be tracked.  To
   make detection difficult, an attacker could decide to use an
   exfiltration process that sends only 10 bytes every Sunday to a
   legitimate cloud service.  If that is not in the normal behavior
   pattern, then this anomaly could be detected by the endpoint.  If the
   process that sends the data or the destination IP address have a bad
   reputation, then they could be stopped.  Though it is very difficult
   to reliably block such an attack and most solutions have a specific
   threshold that needs to be exceeded before it is detected as an
   anomaly.

Taddei, et al.           Expires January 9, 2020               [Page 24]
Internet-Draft                    CLESS                        July 2019

10.4.  Suboptimality and gray areas

10.4.1.  Stolen credentials

   Stolen credentials and misuse of system tools such as RDP, Telnet or
   SSH are a valid scenario during attacks.  An attacker can use stolen
   credentials to remotely log into a system and access data or execute
   commands in this context like the legitimate user might do.  An
   endpoint security solution can restrict access from specific IP
   addresses, but this is difficult in a dynamic environment and when an
   attacker might have already compromised a trusted device and misuse
   it as a stepping stone for lateral movement.  The endpoint could
   perform additional checks of the source device, such as verifying
   installed applications and certain conditions.  Again this will not
   work in all scenarios, e.g. a hijacked valid device during lateral
   movement.

   This means that the system will not be able to simply block the
   connection if the authentication with the stolen credentials
   succeeds.  A multi factor authentication (MFA) could limit the use of
   stolen credentials, but depending on the system used and the
   determination of the attacker they might be able to bypass this
   hurdle as well e.g. cloning a SIM card to read text message codes.

   As a next step, a solution on the endpoint can monitor the behavior
   of the logged in user and determine if it represents expected normal
   behavior.  Unfortunately, there is the chance for false positives
   that might block legitimate actions, hence the rules are usually not
   applied too tightly.  The system can monitor for suspicious behavior,
   similar to malware detection, where every action is carefully
   analyzed and all activity is tracked.  For example if the SSH user is
   adding all files to archives with passwords and then deletes the
   original files in the file explorer, then this could result in a
   ransomware case scenario.  If only a few files are processed per
   hour, then this activity will be very difficult for the endpoint to
   distinguish from normal activity, in order to flag it as malicious.

   The problem of attackers blending in with normal activity is one of
   the biggest challenges with so called living off the land attack
   methods.  The attacker chooses to keep their profile low by not
   installing any additional binary files on the system, but instead
   misuses legitimate system tools to carry out their malicious intent.
   This means that there is no malware file that could be identified and
   the detection relies solely on other methods such as behaviour based
   monitoring [LOTLSYMC].

   If information is shared across multiple endpoints, then each one
   could learn from the others and see how many connections came in from

Taddei, et al.           Expires January 9, 2020               [Page 25]
Internet-Draft                    CLESS                        July 2019

   that source, what files were involved and what behavior the clients
   exhibited.  This crowd wisdom approach would allow blocking rules to
   be applied after the first incident across multiple endpoints.

10.4.2.  Zero Day Vulnerability

   +-------------+-----------------------------------------------------+
   | Description | An attacker exploits a zero day vulnerability or    |
   |             | any recent vulnerability.                           |
   +-------------+-----------------------------------------------------+
   | UE          | In theory this scenario could be handled by the     |
   |             | endpoint security: a) Once the intrinsic security   |
   |             | system has been patched, exploitation of the        |
   |             | vulnerability can be prevented. b) The add-on       |
   |             | security with enhanced capabilities or updated      |
   |             | methods can detect and mitigate the vulnerability.  |
   |             | It does not necessarily require the official patch. |
   |             |                                                     |
   | Challenge   | In practice many systems remain vulnerable to a     |
   |             | vulnerability months or even years after a security |
   |             | fix has been released. Moreover there is a big gap  |
   |             | between when a vulnerability is disclosed and when  |
   |             | a security fix is available. Also there is a big    |
   |             | gap between when a security fix is available and    |
   |             | when the security fix is actually applied. A recent |
   |             | study over three years, examined the patching time  |
   |             | of 12 client-side and 112 server-side applications  |
   |             | in enterprise hosts and servers. It took over 6     |
   |             | months on average to patch 90% of the population    |
   |             | across all vulnerabilities. [NDSSPATCH]. We note    |
   |             | too: "The patching of servers is overall much worse |
   |             | than the patching of client applications. On        |
   |             | average a server application remains vulnerable for |
   |             | 7.5 months."                                        |
   |             |                                                     |
   | References  | [ZERODAY1][ZERODAY2]                                |
   +-------------+-----------------------------------------------------+

10.4.3.  Port scan over the network

   An infected machine, let's say a Mirai bot on a router, is scanning a
   class B network for IP addresses with TCP port 80 open.  The malware
   can slow it down to 1 IP address per 5 seconds (or any other
   threshold) and it can go in randomized order (like for example the
   nmap tool does) in order to make it difficult to find a sequential
   pattern.  To increase detection difficulties, legitimate requests to
   existing web servers can be added in at random intervals.

Taddei, et al.           Expires January 9, 2020               [Page 26]
Internet-Draft                    CLESS                        July 2019

   An endpoint solution might be able to detect this behaviour,
   depending on the threshold, but it will be difficult.  At some point
   the pattern will be similar to browsing the web, so either the
   endpoint blocks the bot scanning and also the user from surfing, or
   it allows both.

   To make it even harder, the attacker can use a botnet that
   communicates over peer-to-peer (P2P) or a central command and control
   server (C&C) and then distribute the scan load over multiple hosts.
   This means each endpoint only scans a subset, let's say 100 IP
   addresses, but all 1,000 bots scan a total of 100,000 IP addresses.

   This attack is difficult to detect by a reasonable threshold on each
   endpoint individually.  If the endpoints talk to each other and
   exchange information, then a collective decision can be made on the
   bigger picture of the bot traffic.

   Another option for the endpoint solution is to block the bot malware
   from operating on the computer, for example by detecting the
   installation, analyzing the behavior of the process or by preventing
   the binary from accessing the network.  This includes blocking any
   form of communication for the process to its C&C server, regardless
   of if it is using a P2P network or misusing legitimate system tools
   or browsers to communicate with the Internet.  Blocking indirect
   communication over system tools as part of living off the land
   tactics, can be very challenging.

   See [BOT]

10.4.4.  DDoS attacks

   For this example let us consider a botnet of 100,000 compromised
   computers and each one sends a burst of traffic to a remote target,
   for one second each, alternating in groups.  This will generate some
   waves of pulse attack traffic.  Similar comments can be made about
   overall pulsed DDoS attacks [PDDoS].

   A solution on the endpoint can attempt to detect the outgoing
   traffic.  If the DoS attack is volume based and the time span of each
   pulse is large enough or the repeating frequency for each bot is
   high, then detection with thresholds on the endpoint is feasible.  It
   is different, if it is an application layer DoS attack, where the
   logic of the receiving application is targeted, for example with too
   many search queries in HTTP GET requests.  This would flood the
   backend server with intensive search requests, which can result in
   the web site no longer being responsive.  Such attacks can succeed
   with a low amount of requests being sent, especially if its
   distributed over a botnet.  This makes it very difficult for a single

Taddei, et al.           Expires January 9, 2020               [Page 27]
Internet-Draft                    CLESS                        July 2019

   endpoint to detect such an ongoing attack, without knowledge from
   other endpoints or the network.

   Another option for the endpoint solution is to block the bot malware
   from operating on the computer, for example by detection the
   installation, analyzing the behavior of the process or by preventing
   the binary from accessing the network.  This includes blocking any
   form of communication for the process to its C&C server, regardless
   of if it is using a P2P network or misusing legitimate system tools
   or browsers to communicate with the Internet.  Blocking indirect
   communication over system tools as part of living off the land
   tactics, can be very challenging.

11.  Learnings from production data

   From the above limited considerations we can now check what we see
   from real production data using

   o  the method described in [MONEYBALL]

   o  the anonymised production data of Symantec MSS production for the
      past 3 months

   The core idea is to consider, based on all the imperfections we
   started to list above including the 'grey areas', that cybersecurity
   analysts are often presented with suspicious machine activity that
   does not conclusively indicate a compromise, resulting in undetected
   incidents or costly investigations into the most appropriate remedial
   actions.

   As Managed Security Services Providers (MSSP's) are confronted with
   these data quality issues, but also possess a wealth of cross-product
   security data that enables innovative solutions, we decided to use
   the Symantec MSS service for the past 3 months.  The Symantec MSS
   service monitors over 100 security products from a wide variety of
   security vendors for hundreds of enterprise class customers from all
   verticals.

   We selected the subset of customers using the service that deploy
   both network and endpoint security products to determine which types
   of security incidents were most likely to be detected by endpoint
   products vs. network products.  In doing so, we were particularly
   interested in identifying which categories of incidents are detected
   by endpoint products and not network products, and vice versa.  Thus,
   we examined prevalent categories of incidents for which the only
   actionable security alerts were predominantly produced by one type of
   security product and not the other.  To do so, we extracted all
   security incidents detected by Symantec MSS on behalf of hundreds of

Taddei, et al.           Expires January 9, 2020               [Page 28]
Internet-Draft                    CLESS                        July 2019

   customers that deploy both network and endpoint security products,
   over a three-month period from December 2018 through the end of
   February 2019.  We acknowledge that some attacks might have been
   blocked by the first product and therefore have never been seen by
   the next security solution, which influences the final numbers.

   With this in mind, we could identify incidents based on:

   +------------+------------------------------------------------------+
   | Severity   | 4 - Emergency, 3 - Critical, 2 - Warning, 1 -        |
   |            | Informational                                        |
   +------------+------------------------------------------------------+
   | Incident   | Malicious Code, Deception Activity, Improper Usage,  |
   | Category   | Investigation, etc.                                  |
   |            |                                                      |
   | Incident   | Trojan Horse Infection, Suspicious DGA Activity,     |
   | Type       | Suspicious Traffic, Suspicious URL Activity,         |
   |            | Backdoor infection, etc.                             |
   |            |                                                      |
   | # network  | Amount of network only security incidents            |
   | incidents  |                                                      |
   |            |                                                      |
   | # all      | What is the total amount of incidents on all         |
   | incidents  | security solutions                                   |
   |            |                                                      |
   | Percentage | Percentage of network security only incidents        |
   +------------+------------------------------------------------------+

   We ended up with

   o  Hundreds of thousands of security incidents

   o  which we could categorize in 275 incident types by category and
      severity (triplets Severity-Category-Type)

   o  out of which we searched how many incidents of each type were
      detected by a network security product and missed by deployed
      endpoint security products at least 75% of the time or vice versa

11.1.  Endpoint only incidents

   The categories of incidents that are detected primarily by endpoint
   security products are fairly intuitive.  They consist primarily of
   detections of file-based threats and detection of malicious behaviors
   through monitoring of system and network behavior at the process
   level.  The most prevalent of these behavioral detections include
   detections of suspicious URLs based on heuristics and blacklists of
   IP addresses or domain names.  Since most of these alerts are not

Taddei, et al.           Expires January 9, 2020               [Page 29]
Internet-Draft                    CLESS                        July 2019

   corroborated by network products, it seems probable that the
   blacklists associated with network products tend to be more focused
   on attacks while host-based intrusion prevention system alerts focus
   more on malware command and control traffic.  Most other behavioral
   detections at the endpoint provide alerts based on system behavior
   that is deemed dangerous and symptomatic of malicious intent by a
   malicious or infected process.  The highest severity incidents
   detected on endpoints are instances of post-compromise outbound
   network behavior that are symptomatic of command and control
   communications traffic, but these did not show up as being primarily
   detected by endpoint products as they are frequently corroborated by
   network-based alerts.

11.2.  Security incidents detected primarily by network security
       products

   Perhaps less intuitive are the results of examining categories of
   security incidents that are detected primarily by network security
   products and only rarely corroborated by endpoint security products.
   Below we provide details regarding incident categories for which a
   network security product produced a detection and for which there
   were no actionable endpoint alerts for at least 75% of the incidents
   in the category.

   In our study we found 32 incident type, category, and severity
   triplets of this type.  The following categories critical incident
   types were reported by MSS customers, and we discuss each in turn in
   decreasing order of prevalence:

11.2.1.  Unauthorized external vulnerability scans

   Perhaps unsurprisingly, unauthorized external attempts to scan
   corporate resources for vulnerabilities and other purposes are
   detected in large volumes by a broad variety of network-focused
   security products. 79% of incidents of this type were detected by
   network security products with critical-severity alerts, these
   security incident detections are not accompanied by any actionable
   endpoint alerts, despite the fact that endpoint security products are
   deployed by these enterprises.  This category of threats encompasses
   a broad variety of attacks, the most prevalent of which are the
   following: Horizontal scans, SQL injection attacks, password
   disclosure vulnerabilities, directory traversal attacks, and
   blacklist hits.  Of these categories of detections, horizontal scans
   stand out as the category of detection that endpoint-security
   products are least likely to detect on their own.

Taddei, et al.           Expires January 9, 2020               [Page 30]
Internet-Draft                    CLESS                        July 2019

11.2.2.  Unauthorized internal vulnerability scans

   Unauthorized internal vulnerability scans, though less frequent, are
   more alarming, as they are likely to represent possible post-
   compromise activity.  We note that the Managed Security Service works
   with its customers to maintain lists of devices that are authorized
   to perform internal vulnerability scans, and their activity is
   reported separately at a lower levels of incident severity. 89% of
   detected unauthorized internal vulnerability scans are detected by
   network products without any corroborating actionable alerts from
   endpoint security products.  As compared to unauthorized external
   scan incidents, internal hosts that perform vulnerability scans are
   far more active and the fraction of alerts that detect horizontal
   scans is higher, representing half of the total alerts generated.
   Alerts focused on Network-Behavior Anomaly Detection also appear for
   internal hosts.

11.2.3.  Malware downloads resulting in exposed endpoints

   This category of threats is generally detected by network security
   appliances.  Despite these enterprises being purchasers of endpoint
   security products, 76% of the incidents detected by the network
   security products do not show a corresponding alert by an endpoint
   security product.  A broad variety of network appliances contributed
   to the detection of a diverse collection of malware samples.

11.2.4.  Exploit kit infections

   This category of infections represents instances in which the
   customer's machines are exposed to exploit kits.  These threats were
   detected by network appliances that extract suspicious URLs from
   network traffic taps and use a combination of sandbox technology and
   blacklists to identify websites that deploy a variety of exploit kits
   that were not being caught by endpoint security products.  In this
   three month time period, the most prevalent categories of exploit
   kits detected involved redirections to the Magnitude exploit kit and
   exploit kits associated with phishing scams and attempts to expose
   users to fake Anti-Virus warnings and tools.  A breakdown of the
   results is included below:

Taddei, et al.           Expires January 9, 2020               [Page 31]
Internet-Draft                    CLESS                        July 2019

              +---------------------+-----------------------+
              | Severity            | 3 - Critical          |
              +---------------------+-----------------------+
              | Incident Category   | Malicious Code        |
              |                     |                       |
              | Incident Type       | Exploit Kit Infection |
              |                     |                       |
              | # network incidents | 26                    |
              |                     |                       |
              | # all incidents     | 26                    |
              |                     |                       |
              | Percentage          | 100%                  |
              +---------------------+-----------------------+

   The network security product that detected these incidents produced
   the following alerts:

   o  Advanced Malware Payloads

   o  Exploit.Kit.FakeAV

   o  Exploit.Kit.Magnitude

   o  Exploit.Kit.MagnitudeRedirect

   o  Exploit.Kit.PhishScams

   o  HTMLMagnitudeLandingPage

11.2.5.  Attacks against servers

   In addition to detecting the aforementioned critical security
   incident categories, network security devices frequently detect a
   broad variety of attacks against servers that usually lack
   corroboration at the endpoint.  Most server attacks are not matched
   by endpoint protection alerts: 62% are unmatched for critical
   incidents, and 88% are unmatched as lower severity incidents.  This
   category of incidents is the most prevalent category of incidents
   detected primarily by network products, but they are usually rated
   lower in severity than the aforementioned classes of alerts as they
   are very commonplace.  Even when these alerts are corroborated by
   endpoint protection alerts, the endpoint alerts are often low in
   severity, as in the case of file-based threats that appear to have
   been blocked or successfully cleaned up by an Anti-Virus solution.
   The challenge in taking action against server attacks is that it can
   be difficult to assess which of these attacks were successful in
   causing actual damage, and for this reason, for the fraction of
   server attacks that demonstrate corroborating endpoint security

Taddei, et al.           Expires January 9, 2020               [Page 32]
Internet-Draft                    CLESS                        July 2019

   alerts, even if of low severity, should be examined.  It is
   interesting to note the cooperative role played by both network and
   endpoint security devices in these instances.

12.  Regulatory Considerations

   This section will briefly look at the regulatory landscape and
   develop a specific view on the impact on endpoints with the goal to
   see what we might be able to learn.

   Legal requirements, compliance, regulatory frameworks and mandatory
   reporting are no longer separate from any security evaluation,
   process or requirement within an organisation, enterprise system or
   intranet.  It is essential to look at the technical and regulatory
   approaches together.  This section will look at two examples of legal
   requirements and guidance:

   (1) IoT security (2) Network infrastructure

   This section is by no means complete, but it does a discussion on
   this aspect of endpoint and ecosystem regulation.

12.1.  IoT Security

   IoT security regulation is emerging in the form of voluntary
   frameworks and self-assessments that relate to endpoint security
   issues.. These frameworks focus first on the end point, or mobile
   device, in the IoT environment and then on the holistic ecosystem
   itself.

   In 2017 the National Institute of Standards and Technology released
   its draft IoT Cybersecurity Framework based on consultations and
   interviews with all stakeholders over several years previously
   [NISTIOTP].  Some of the themes which emerged was the need for IoT
   governance, assessment frameworks, review of all aspects of the IoT
   ecosystem and a process for coordinated vulnerability disclosure
   inside an organisation.  As evidenced by the 2018 Endpoint Protection
   and Response Survey by SANS, only 47% of organisations know that
   their endpoints have been breached and a further 20% are unsure
   [EPRSANS].  So a systemic approach from NIST was welcomed and the
   NIST framework became the gold standard for national IoT security
   frameworks.

   Other IoT security frameworks include the Singapore IoT Cyber
   Security Guide from January 2019 and the UK's Secure by Design or The
   Government's Code of Practice for Consumer Internet of Things (IoT)
   Security for manufacturers, with guidance for consumers on smart
   devices at home [IMDAIOTG], [SBDGOVUK].  Once again both look at

Taddei, et al.           Expires January 9, 2020               [Page 33]
Internet-Draft                    CLESS                        July 2019

   securing the IoT device or endpoint, but also security for the entire
   value chain of the IoT system.  The Singapore framework makes the
   point about the entire system clear, "Similar to any system, an IoT
   system is as secure as its weakest link.  It is thus important to
   ensure that proper security considerations and measures are put in
   place for both the implementation and operational stages of the
   deployment of any IoT system."  [IMDAIOTG] Finally, the IoT Security
   Foundation, the GSMA and the Internet Society have all released their
   own frameworks for IoT security.  All have similar characteristics
   which focus on the entire value chain and ecosystem, but also on
   vulnerability disclosure and checklist assessments.  What makes each
   of these approaches slightly different is the differing perspectives
   of the organization advocating it.  The GSMA is the mobile trade
   association and so it focuses on mobile devices while the Internet
   Society focuses on the Internet ecosystem and a multistakeholder
   approach.  Systematically underpinning all the frameworks is the
   holistic approach with voluntary best practices and implementation
   based on the needs of the user or organisation adopting the framework
   [IOTSFCF], [GSMAIOT], [ISTRUST].

12.2.  Network infrastructure

   In Europe, the Network and Information Security Directive, which was
   passed in July 2016, require implementation by each European member
   state with a threefold aim.  First, to put into place a national
   strategy for network and infrastructure security including best
   practices, guidelines, training and stakeholder consultations.
   Second, to coordinate national CSIRTs with CERT-EU and third to
   provide incident control and response systems for critical
   infrastructure and digital services [EURLEX].  This Directive
   demonstrates the importance give across the EU to network resilience
   and incident reporting.  While securing the endpoint is acknowledged,
   the focus is on ensuring the security of European interoperable
   networks.  In short, the importance of the security of the network
   including incident response shows that it isn't only the endpoints
   that should be the focus of the regulation and legal frameworks.

12.3.  Auditing and Assessment

   This section will talk about other risk assessment and auditing
   regulatory requirements beyond the NIS directive.

   One example of risk assessment as a regulatory requirement is the New
   York State law 23 NYCRR 500 of the Regulations of the Superintendent
   of Financial Services (Cybersecurity Requirements for Financial
   Services Companies).  Among the requirements, audit, risk assessment
   and risk reporting are included like,

Taddei, et al.           Expires January 9, 2020               [Page 34]
Internet-Draft                    CLESS                        July 2019

   (2) include audit trails designed to detect and respond to
   Cybersecurity Events that have a reasonable likelihood of materially
   harming any material part of the normal operations of the Covered
   Entity.  [NYCYBER]

12.4.  Privacy Considerations

   We may consider a specific focus on privacy in the future.

13.  Human Rights Considerations

   This section may develop a specific view of requirements, limits and
   constraints coming from Human Rights perspective on endpoint
   security.

14.  Security Considerations

   This document is about Security Considerations

15.  IANA Considerations

   This document has no actions for IANA

16.  Informative References

   [ADAPTURE]
              Cullen, T., "Limits of endpoint only", July 2017,
              <https://www.adapture.com/blog/
              evaluating-leading-endpoint-security-vendors/>.

   [AMT1]     Khandelwal, S., "Explained - How Intel AMT Vulnerability
              Allows to Hack Computers Remotely", May 2017,
              <https://thehackernews.com/2017/05/
              intel-amt-vulnerability.html>.

   [AMT2]     Symantec, ., "Web Attack Intel AMT Privilege Escalation
              CVE-2017-5689", 2017,
              <https://www.symantec.com/security_response/
              attacksignatures/detail.jsp?asid=29888>.

   [ATTACK]   "MITRE ATT&CK", n.d., <https://attack.mitre.org>.

   [BOT]      Marinho, R., "Exploring a P2P transient botnet - From
              Discovery to Enumeration", July 2017,
              <https://morphuslabs.com/exploring-a-p2p-transient-botnet-
              from-discovery-to-enumeration-e72870354950>.

Taddei, et al.           Expires January 9, 2020               [Page 35]
Internet-Draft                    CLESS                        July 2019

   [CANDID1]  Wueest, C., "How my TV got infected with ransomware and
              what you can learn about it", November 2015,
              <https://www.symantec.com/connect/blogs/how-my-tv-got-
              infected-ransomware-and-what-you-can-learn-it>.

   [CANDID2]  Dickson, B., "Millions of smart TVs are vulnerable to
              hackers", February 2014,
              <https://www.dailydot.com/debug/protect-smart-tv/>.

   [CAPEC]    "MITRE CAPEC", n.d.,
              <https://capec.mitre.org/data/definitions/3000.html>.

   [ENISA]    ENISA, ., "Baseline Security Recommendations for IoT in
              the context of Critical Information Infrastructures",
              November 2017, <https://www.enisa.europa.eu/publications/
              baseline-security-recommendations-for-iot>.

   [EPPEDR]   Redscan, ., "EPP and EDR - What's the difference?", June
              2018, <https://www.redscan.com/news/
              epp-vs-edr-whats-the-difference/>.

   [EPPGUIDE]
              "IT Pro's Guide to Endpoint Protection", n.d.,
              <https://www.barkly.com/
              it-pros-guide-to-endpoint-protection>.

   [EPPSECURITY]
              Hunt, J., "Advantages and Disadvantages of Three Top
              Endpoint Security Vendors", n.d.,
              <https://www.adapture.com/blog/
              evaluating-leading-endpoint-security-vendors/>.

   [EPRSANS]  Neely, L., "Endpoint Protection and Response A SANS
              Survey", June 2018, <https://www.sans.org/reading-
              room/whitepapers/clients/paper/38460>.

   [EPTAXONOMY]
              MacFadden, M., "Endpoint Taxonomy for CLESS", July 2019,
              <https://www.ietf.org/id/
              draft-mcfadden-smart-endpoint-taxonomy-for-cless-00.txt>.

   [ERICSSON]
              Ericsson, ., "Internet of Things forecast", n.d.,
              <https://www.ericsson.com/en/mobility-report/
              internet-of-things-forecast>.

Taddei, et al.           Expires January 9, 2020               [Page 36]
Internet-Draft                    CLESS                        July 2019

   [EURLEX]   EUP, ., "Directive (EU) 2016/1148", July 2016,
              <https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=urise
              rv:OJ.L_.2016.194.01.0001.01.ENG&toc=OJ:L:2016:194:TOC>.

   [FLAMER]   Symantec, ., "W32.Flamer Microsoft Windows Update Man-in-
              the-Middle", June 2012,
              <https://www.symantec.com/connect/blogs/
              w32flamer-microsoft-windows-update-man-middle>.

   [GARTNERIOT]
              Van der Meulen, R., "Gartner Says 8.4 Billion Connected
              Things Will be in Use in 2017, Up 31 percent from 2016",
              February 2017, <https://www.gartner.com/en/newsroom/press-
              releases/2017-02-07-gartner-says-8-billion-connected-
              things-will-be-in-use-in-2017-up-31-percent-from-2016>.

   [GARTNERREPORT]
              Crotty, J., "New Gartner Report Redefines Endpoints
              Protection for 2018", January 2018,
              <https://www.crowdstrike.com/blog/new-gartner-report-
              redefines-endpoint-protection-for-2018/>.

   [GSMAIOT]  GSMA, ., "GSMA IoT Security Guidelines and Assessment",
              n.d., <https://www.gsma.com/iot/iot-security/
              iot-security-guidelines/>.

   [HSTODAY]  Hstoday, ., "Layered Approach Critical to Effective
              Endpoint Protection", October 2016,
              <https://www.hstoday.us/channels/federal-state-local/
              layered-approach-critical-to-effective-endpoint-
              protection/>.

   [I-D.draft-mcfadden-smart-endpoint-taxonomy-for-cless-00]
              McFadden, M., "Endpoint Taxonomy for CLESS", draft-
              mcfadden-smart-endpoint-taxonomy-for-cless-00 (work in
              progress), July 2019.

   [IMDAIOTG]
              IMDA, ., "IMDA IoT Cyber Security Guide", January 2019,
              <https://www.imda.gov.sg/-/media/imda/files/
              regulation-licensing-and-consultations/consultations/
              open-for-public-comments/
              consultation-for-iot-cyber-security-guide/
              imda-iot-cyber-security-guide.pdf>.

Taddei, et al.           Expires January 9, 2020               [Page 37]
Internet-Draft                    CLESS                        July 2019

   [IOTPATCHING]
              Rogers, D., "Handling vulnerabilities as an IoT vendor",
              December 2018, <https://www.iotsecurityfoundation.org/
              less-than-10-of-consumer-iot-companies-follow-
              vulnerability-disclosure-guidelines/>.

   [IOTSFCF]  IoTSF, ., "IoT Security Compliance Framework", December
              2018, <https://www.iotsecurityfoundation.org/
              best-practice-guidelines/>.

   [ISTRUST]  ISOC, ., "Internet of Things (IoT) Trust Framework v2.5",
              May 2018,
              <https://www.internetsociety.org/resources/doc/2018/
              iot-trust-framework-v2-5/>.

   [LOJAX]    ESET, ., "LoJax First UEFI rootkit found in the wild,
              courtesy of the Sednit group", September 2018,
              <https://www.welivesecurity.com/2018/09/27/lojax-first-
              uefi-rootkit-found-wild-courtesy-sednit-group/>.

   [LOTLSYMC]
              Wueest, C., "Living off the land and fileless attack
              techniques", July 2017,
              <https://www.symantec.com/content/dam/symantec/docs/
              security-center/white-papers/istr-living-off-the-land-and-
              fileless-attack-techniques-en.pd>.

   [MIRAI1]   Symantec, ., "Mirai, what you need to know about the
              botnet behind recent major DDoS attacks", October 2016,
              <https://www.symantec.com/connect/blogs/mirai-what-you-
              need-know-about-botnet-behind-recent-major-ddos-attacks>.

   [MIRAI2]   Krebsonsecurity, ., "19 Mirai Botnet Authors Avoid Jail
              Time", September 2018,
              <https://krebsonsecurity.com/tag/mirai-botnet/>.

   [MONEYBALL]
              Roundy, K., "Predicting Cyber Threats with Virtual
              Security Products. ACSAC", 2017,
              <https://www.cc.gatech.edu/~dchau/
              papers/17-acsac-moneyball.pdf>.

   [NDSSPATCH]
              Caballero, J., "Mind Your Own Business A Longitudinal
              Study of Threats and Vulnerabilities in Enterprises",
              February 2019, <https://www.ndss-symposium.org/wp-
              content/uploads/2019/02/
              ndss2019_03B-1-2_Kotzias_paper.pdf>.

Taddei, et al.           Expires January 9, 2020               [Page 38]
Internet-Draft                    CLESS                        July 2019

   [NETTODAY]
              Dix, J., "Layered Security Defenses What layer is most
              critical network or endpoint", July 2011,
              <https://www.networkworld.com/article/2220204/tech-
              debates/layered-security-defenses--what-layer-is-most-
              critical--network-or-endpoint-.html>.

   [NINESIGNS]
              Smith, K., "9 signs your endpoint security isn't working",
              May 2017, <https://securelement.com/9-signs-your-endpoint-
              security-isnt-working/>.

   [NISTIOTP]
              NIST, ., "NIST Cybersecurity for IoT Program", November
              2016, <https://www.nist.gov/programs-projects/
              nist-cybersecurity-iot-program>.

   [NYCYBER]  NYCRR, ., "See 3 NYCRR 500 of the Regulations of the
              Superintendent of Financial Services (Cybersecurity
              Requirements for Financial Services Companies)", n.d.,
              <https://www.dfs.ny.gov/docs/legal/regulations/adoptions/
              dfsrf500txt.pdf>.

   [OWASP]    OWASP, ., "Defense in depth definition", August 2015,
              <https://www.owasp.org/index.php/Defense_in_depth>.

   [PDDoS]    Seals, T., "Pulse-Wave DDoS Attacks Mark a New Tactics in
              Q2", October 2017, <https://www.infosecurity-
              magazine.com/news/pulsewave-ddos-attacks-mark-q2/>.

   [SBDGOVUK]
              UK, GOV., "Secure by Design", February 2019,
              <https://www.gov.uk/government/collections/
              secure-by-design>.

   [SGX1]     Claburn, T., "Intel SGX safe room easily trashed by white-
              hat hacking marauders Enclave malware demoed", February
              2019, <https://www.theregister.co.uk/2019/02/12/
              intel_sgx_hacked/>.

   [SGX2]     Cimpanu, C., "Researchers hide malware in Intel SGX
              enclaves", February 2019, <https://www.zdnet.com/article/
              researchers-hide-malware-in-intel-sgx-enclaves/>.

   [SQL]      Cobb, M., "SQL injection detection tools and prevention
              strategies", November 2009,
              <https://www.computerweekly.com/tip/
              SQL-injection-detection-tools-and-prevention-strategies>.

Taddei, et al.           Expires January 9, 2020               [Page 39]
Internet-Draft                    CLESS                        July 2019

   [STATISTA1]
              Statista, ., "Internet of Things (IoT) connected devices
              installed base worldwide from 2015 to 2025 (in billions)",
              n.d., <https://www.statista.com/statistics/471264/
              iot-number-of-connected-devices-worldwide/>.

   [STATISTA2]
              Statista, ., "Size of Internet of Things market worldwide
              in 2014 and 2020 by industry (in billion U.S dollars)",
              n.d., <https://blogs-
              images.forbes.com/louiscolumbus/files/2017/12/
              size-of-IoT-Market-globally-2014-to-2020.jpg>.

   [TEEP]     Cam-Winget, N., "Trust Execution Environment Protocol",
              March 2018, <https://datatracker.ietf.org/wg/teep/about>.

   [USCERT]   Michael, C., "Principles of defense-in-depth", September
              2005, <https://www.us-
              cert.gov/bsi/articles/knowledge/principles/
              defense-in-depth>.

   [ZERODAY1]
              McHugh, J., "Windows of Vulnerability A Case Study
              Analysis", 2000, <http://www.cs.colostate.edu/~cs635/
              Windows_of_Vulnerability.pdf>.

   [ZERODAY2]
              Plattner, B., "Large-Scale Vulnerability Analysis",
              September 2006, <http://citeseerx.ist.psu.edu/viewdoc/
              download?doi=10.1.1.173.3056&rep=rep1&type=pdf>.

Appendix A.  Contributors

   o  Arnaud Taddei
      Symantec
      arnaud_taddei@symantec.com

   o  Bret Jordan
      Symantec
      bret_jordan@symantec.com

   o  Candid Wueest
      Symantec
      candid_wueest@symantec.com

   o  Chris Larsen
      Symantec
      chris_larsen@symantec.com

Taddei, et al.           Expires January 9, 2020               [Page 40]
Internet-Draft                    CLESS                        July 2019

   o  Andre Engel
      Symantec
      andre_ngel@symantec.com

   o  Kevin Roundy
      Symantec
      kevin_roundy@symantec.com

   o  Yuqiong Sun
      Symantec
      Yuqiong_Sun@symantec.com

   o  David Wells
      Symantec
      David_Wells@symantec.com

   o  Dominique Lazanski
      Last Press Label
      dml@lastpresslabel.com

Authors' Addresses

   Arnaud Taddei
   Symantec Corporation
   350 Ellis Street
   Mountain View  CA 94043
   USA

   Email: arnaud_taddei@symantec.com

   Candid Wueest
   Symantec Corporation
   350 Ellis Street
   Mountain View  CA 94043
   USA

   Email: candid_wueest@symantec.com

   Kevin A. Roundy
   Symantec Corporation
   350 Ellis Street
   Mountain View  CA 94043
   USA

   Email: kevin_roundy@symantec.com

Taddei, et al.           Expires January 9, 2020               [Page 41]
Internet-Draft                    CLESS                        July 2019

   Dominique Lazanski
   Last Press Label
   Flat 1, 109A Columbia Road
   London  E2 7RL
   UK

   Email: dml@lastpresslabel.com

Taddei, et al.           Expires January 9, 2020               [Page 42]