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Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                 S. Rose
Expires: November 19, 2020                                          NIST
                                                            May 18, 2020


                         SBOM Extension for MUD
                     draft-lear-opsawg-mud-sbom-00

Abstract

   Software bills of materials (SBOMs) are formal descriptions of what
   pieces of software are included in a product.  This memo specifies a
   means for manufacturers to state how SBOMs may be retrieved through
   an extension to manufacturer usage descriptions (MUD).

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 November 19, 2020.

Copyright Notice

   Copyright (c) 2020 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
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  How This Information Is Used  . . . . . . . . . . . . . .   3
     1.2.  SBOM formats  . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Discussion points . . . . . . . . . . . . . . . . . . . .   3
   2.  The mud-sbom extension model extension  . . . . . . . . . . .   4
   3.  The mud-sbom augmentation to the MUD YANG model . . . . . . .   4
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Without ACLS  . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Located on the Device . . . . . . . . . . . . . . . . . .   8
     4.3.  SBOM Obtained from Contact Information  . . . . . . . . .   9
     4.4.  With ACLS . . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  MUD Extension . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Well-Known Prefix . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Changes from Earlier Versions  . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Manufacturer Usage Descriptions (MUD) [RFC8520] provides a means for
   devices to identify what they are and what sort of network access
   they need.  This memo specifies a YANG model [RFC6991] for reporting
   and a means for transmitting the report, and appropriate extensions
   to the MUD file to indicate how to report and how often.

   Software bills of material (SBOMs) are descriptions of what software,
   including versionioning and dependencies, a device contains.  There
   are different SBOM formats such as Software Package Data Exchange
   [SPDX] and Software Identity Tags [SWID].

   This memo extends the MUD YANG schema to provide location information
   of an SBOM.

   These SBOMs are typically found in one of three ways:

   o  on devices themselves

   o  on a web site (e.g., via URI)

   o  through direct contact with the manufacturer.





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   Some devices will have interfaces that permit direct SBOM retrieval.
   Examples of these interfaces might be 'ssh' or an HTTP endpoint for
   retrieval.  There may also be private interfaces as well.

   When a web site is used, versioning information about the SBOM is
   implicit based on the MUD file.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

1.1.  How This Information Is Used

   SBOMs are used for numerous purposes, including vulnerability
   assessment, license management, and inventory management.  This memo
   provides means for either automated or semi-automated collection of
   that information.  For devices that can output a MUD URL, the
   mechanism may be highly automated.  For devices that have a MUD URL
   in either their documentation or within a QR code on a box, the
   mechanism is semi-automated (someone has to scan the QR code or enter
   the URL).

   Note that SBOMs may change more frequently than access control
   requirements.  A change to software does not necessarily mean a
   change to control channels that are used.  Therefore, it is important
   to retrieve the MUD file as suggested by the manufacturer in the
   cache-validity period.  In many cases, only the SBOM list will have
   been updated.

1.2.  SBOM formats

   There are multiple ways to express an SBOM.  When these are retrieved
   either directly from the device or directly from a web server, tools
   will need to observe the content-type header to determine precisely
   which format is being transmitted.  Because IoT devices in particular
   have limited capabilities, use of a specific Accept: header in HTTP
   or the Accept Option in CoAP is NOT RECOMMENDED.  Instead, backend
   tooling MUST silently discard SBOM information sent with a media type
   that is not understood.

1.3.  Discussion points

   The following is discussion to be removed at time of RFC publication.

   o  Is the model structured correctly?




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   o  Are there other retrieval mechanisms that need to be specified?

   o  Do we need to be more specific in how to authenticate and retrieve
      SBOMs?

   o  What are the implications if the MUD URL is an extension in a
      certificate (e.g. an IDevID cert)?

2.  The mud-sbom extension model extension

   We now formally define this extension.  This is done in two parts.
   First, the extension name "sbom" is listed in the "extensions" array
   of the MUD file.

   Second, the "mud" container is augmented with a list of SBOM sources.

   This is done as follows:

   module: ietf-mud-sbom
     augment /mud:mud:
       +--rw sboms* [version-info]
          +--rw version-info         string
          +--rw (sbom-type)?
             +--:(url)
             |  +--rw sbom-url?      inet:uri
             +--:(local-uri)
             |  +--rw sbom-local*    enumeration
             +--:(contact-info)
                +--rw contact-uri?   inet:uri

3.  The mud-sbom augmentation to the MUD YANG model

<CODE BEGINS>file "ietf-mud-sbom@2020-03-06.yang"
module ietf-mud-sbom {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-mud-sbom";
  prefix mud-sbom;

  import ietf-inet-types {
    prefix inet;
  }
  import ietf-mud {
    prefix mud;
  }

  organization
    "IETF OPSAWG (Ops Area) Working Group";
  contact



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    "WG
     Web: http://tools.ietf.org/wg/opsawg/
     WG List: opsawg@ietf.org
     Author: Eliot Lear lear@cisco.com ";
  description
    "This YANG module augments the ietf-mud model to provide for
     reporting of SBOMs.

     Copyright (c) 2019 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject to
     the license terms contained in, the Simplified BSD License set
     forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for
     full legal notices.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
     NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
     'MAY', and 'OPTIONAL' in this document are to be interpreted as
     described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
     they appear in all capitals, as shown here.  ";

  revision 2020-03-06 {
    description
      "Initial proposed standard.";
    reference
      "RFC XXXX: Extension for MUD Reporting";
  }

  grouping mud-sbom-extension {
    description
      "SBOM extension grouping";
    list sboms {
      key "version-info";
      leaf version-info {
        type string;
        description
          "A version string that is applicable for this SBOM list entry.
           The format of this string is left to the device manufacturer.
           How the network administrator determines the version of
           software running on the device is beyond the scope of this
           memo.";



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      }
      choice sbom-type {
        case url {
          leaf sbom-url {
            type inet:uri;
            description
              "A statically located URI.";
          }
        }
        case local-uri {
          leaf-list sbom-local {
            type enumeration {
              enum coap {
                description
                  "Use COAP schema to retrieve SBOM";
              }
              enum coaps {
                description
                  "Use COAPS schema to retrieve SBOM";
              }
              enum http {
                description
                  "Use HTTP schema to retrieve SBOM";
              }
              enum https {
                description
                  "Use HTTPS schema to retrieve SBOM";
              }
            }
            description
              "The choice of sbom-local means that the SBOM resides at
              a location indicated by an indicted scheme for the
              device in question, at well known location
              '/.well-known/sbom'.  For example, if the MUD file
              indicates that coaps is to be used and the host is
              located at address 10.1.2.3, the SBOM could be retrieved
              at 'coaps://10.1.2.3/.well-known/sbom'.  N.B., coap and
              http schemes are NOT RECOMMENDED.";
          }
        }
        case contact-info {
          leaf contact-uri {
            type inet:uri;
            description
              "This MUST be either a tel, http, https, or
               mailto uri schema that customers can use to
               contact someone for SBOM information.";
          }



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        }
        description
          "choices for SBOM retrieval.";
      }
      description
        "list of methods to get an SBOM.";
    }
  }

  augment "/mud:mud" {
    description
      "Add extension for SBOMs.";
    uses mud-sbom-extension;
  }
}

<CODE ENDS>

4.  Examples

   In this example MUD file that uses a cloud service, the Frobinator
   presents a location of the SBOM in a URL.  Note, the ACLs in a MUD
   file are NOT required, although they are a very good idea for IP-
   based devices.  The first MUD file demonstrates how to get the SBOM
   without ACLs, and the second has ACLs.

4.1.  Without ACLS
























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  {
    "ietf-mud:mud": {
      "mud-version": 1,
      "mud-url": "https://iot-device.example.com/dnsname",
      "last-update": "2019-01-15T10:22:47+00:00",
      "cache-validity": 48,
      "is-supported": true,
      "systeminfo": "device that wants to talk to a cloud service",
      "mfg-name": "Example, Inc.",
      "documentation": "https://frobinator.example.com/doc/frob2000",
      "model-name": "Frobinator 2000",
      "extensions" : [
         "sbom"
        ],
      "sboms" : [
        {
           "version-info" : "FrobOS Release 1.1",
           "sbom-url" : "https://frobinator.example.com/sboms/f20001.1",
        }
      ]
    }
  }

4.2.  Located on the Device

   {
     "ietf-mud:mud": {
       "mud-version": 1,
       "mud-url": "https://iot-device.example.com/dnsname",
       "last-update": "2019-01-15T10:22:47+00:00",
       "cache-validity": 48,
       "is-supported": true,
       "systeminfo": "device that wants to talk to a cloud service",
       "mfg-name": "Example, Inc.",
       "documentation": "https://frobinator.example.com/doc/frob2000",
       "model-name": "Frobinator 2000",
       "extensions" : [
          "sbom"
         ],
       "sboms" : [
         {
            "version-info" : "FrobOS Release 1.1",
            "sbom-local" : "coaps:///.well-known/sbom",
         }
       ]
     }
   }




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4.3.  SBOM Obtained from Contact Information

   {
     "ietf-mud:mud": {
       "mud-version": 1,
       "mud-url": "https://iot-device.example.com/dnsname",
       "last-update": "2019-01-15T10:22:47+00:00",
       "cache-validity": 48,
       "is-supported": true,
       "systeminfo": "device that wants to talk to a cloud service",
       "mfg-name": "Example, Inc.",
       "documentation": "https://frobinator.example.com/doc/frob2000",
       "model-name": "Frobinator 2000",
       "extensions" : [
          "sbom"
         ],
       "sboms" : [
         {
            "version-info" : "FrobOS Release 1.1",
            "contact-uri" : "mailto:sbom-requst@example.com",
         }
       ]
     }
   }

4.4.  With ACLS

{
  "ietf-mud:mud": {
    "mud-version": 1,
    "mud-url": "https://iot-device.example.com/dnsname",
    "last-update": "2019-01-15T10:22:47+00:00",
    "cache-validity": 48,
    "is-supported": true,
    "systeminfo": "device that wants to talk to a cloud service",
    "mfg-name": "Example, Inc.",
    "documentation": "https://frobinator.example.com/doc/frob2000",
    "model-name": "Frobinator 2000",
    "extensions" : [
       "sbom"
      ],
    "sboms" : [
      {
         "version-info" : "FrobOS Release 1.1",
         "sbom-url" : "https://frobinator.example.com/sboms/f20001.1",
      }
    ],
    "from-device-policy": {



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      "access-lists": {
        "access-list": [
          {
            "name": "mud-96898-v4fr"
          },
          {
            "name": "mud-96898-v6fr"
          }
        ]
      }
    },
    "to-device-policy": {
      "access-lists": {
        "access-list": [
          {
            "name": "mud-96898-v4to"
          },
          {
            "name": "mud-96898-v6to"
          }
        ]
      }
    }
  },
  "ietf-access-control-list:acls": {
    "acl": [
      {
        "name": "mud-96898-v4to",
        "type": "ipv4-acl-type",
        "aces": {
          "ace": [
            {
              "name": "cl0-todev",
              "matches": {
                "ipv4": {
                  "ietf-acldns:src-dnsname": "cloud-service.example.com"
                }
              },
              "actions": {
                "forwarding": "accept"
              }
            }
          ]
        }
      },
      {
        "name": "mud-96898-v4fr",
        "type": "ipv4-acl-type",



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        "aces": {
          "ace": [
            {
              "name": "cl0-frdev",
              "matches": {
                "ipv4": {
                  "ietf-acldns:dst-dnsname": "cloud-service.example.com"
                }
              },
              "actions": {
                "forwarding": "accept"
              }
            }
          ]
        }
      },
      {
        "name": "mud-96898-v6to",
        "type": "ipv6-acl-type",
        "aces": {
          "ace": [
            {
              "name": "cl0-todev",
              "matches": {
                "ipv6": {
                  "ietf-acldns:src-dnsname": "cloud-service.example.com"
                }
              },
              "actions": {
                "forwarding": "accept"
              }
            }
          ]
        }
      },
      {
        "name": "mud-96898-v6fr",
        "type": "ipv6-acl-type",
        "aces": {
          "ace": [
            {
              "name": "cl0-frdev",
              "matches": {
                "ipv6": {
                  "ietf-acldns:dst-dnsname": "cloud-service.example.com"
                }
              },
              "actions": {



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                "forwarding": "accept"
              }
            }
          ]
        }
      }
    ]
  }
}

   At this point, the management system can attempt to retrieve the
   SBOM, and determine which format is in use through the content-type
   header on the response to a GET request.

5.  Security Considerations

   SBOMs provide an inventory of software.  If firmware is available to
   an attacker, the attacker may well already be able to derive this
   very same software inventory.  Manufacturers MAY restrict access to
   SBOM information using appropriate authorization semantics within
   HTTP.  In particular, if a system attempts to retrieve an SBOM via
   HTTP, if the client is not authorized, the server MUST produce an
   appropriate error, with instructions on how to register a particular
   client.  One example may be to issue a certificate to the client for
   this purpose after a registration process has taken place.  Another
   example would involve the use of OAUTH in combination with a
   federations of SBOM servers.

   To further mitigate attacks against a device, manufacturers SHOULD
   recommend access controls through the normal MUD mechanism.

6.  IANA Considerations

6.1.  MUD Extension

   The IANA is requested to add "controller-candidate" to the MUD
   extensions registry as follows:

     Extension Name: sbom
     Standard reference: This document


6.2.  Well-Known Prefix

   The following well known URI is requested in accordance with
   [RFC8615]:





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     URI suffix: "sbom"
     Change controller: "IETF"
     Specification document: This memo
     Related information:  See ISO/IEC 19970-2 and SPDX.org


7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8520]  Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", RFC 8520,
              DOI 10.17487/RFC8520, March 2019,
              <https://www.rfc-editor.org/info/rfc8520>.

   [RFC8615]  Nottingham, M., "Well-Known Uniform Resource Identifiers
              (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
              <https://www.rfc-editor.org/info/rfc8615>.

7.2.  Informative References

   [SPDX]     The Linux Foundation, "SPDX Specification 2.1", 2016.

   [SWID]     ISO/IEC, "Information technology -- IT asset management --
              Part 2: Software identification tag", ISO 19770-2:2015,
              2015.

Appendix A.  Changes from Earlier Versions

   Draft -00:

   o  Initial revision






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Authors' Addresses

   Eliot Lear
   Cisco Systems
   Richtistrasse 7
   Wallisellen  CH-8304
   Switzerland

   Phone: +41 44 878 9200
   Email: lear@cisco.com


   Scott Rose
   NIST
   100 Bureau Dr
   Gaithersburg MD  20899
   USA

   Phone: +1 301-975-8439
   Email: scott.rose@nist.gov































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