Discovering And Accessing Software Bills of Materials
draft-ietf-opsawg-sbom-access-01

Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                 S. Rose
Expires: 19 November 2021                                           NIST
                                                             18 May 2021

         Discovering And Accessing Software Bills of Materials
                    draft-ietf-opsawg-sbom-access-01

Abstract

   Software bills of materials (SBOMs) are formal descriptions of what
   pieces of software are included in a product.  This memo specifies a
   different means for SBOMs to be retrieved.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 19 November 2021.

Copyright Notice

   Copyright (c) 2021 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.  Cases Not Addressed . . . . . . . . . . . . . . . . . . .   3
     1.2.  How This Information Is Used  . . . . . . . . . . . . . .   4
     1.3.  SBOM formats  . . . . . . . . . . . . . . . . . . . . . .   4
     1.4.  Discussion points . . . . . . . . . . . . . . . . . . . .   4
   2.  The .well-known/sbom endpoint set . . . . . . . . . . . . . .   5
   3.  The mud-sbom extension model extension  . . . . . . . . . . .   5
   4.  The mud-sbom augmentation to the MUD YANG model . . . . . . .   5
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Without ACLS  . . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Located on the Device . . . . . . . . . . . . . . . . . .   9
     5.3.  SBOM Obtained from Contact Information  . . . . . . . . .   9
     5.4.  With ACLS . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  MUD Extension . . . . . . . . . . . . . . . . . . . . . .  13
     7.2.  Well-Known Prefix . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  Changes from Earlier Versions  . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Software bills of material (SBOMs) are descriptions of what software,
   including versioning and dependencies, a device contains.  There are
   different SBOM formats such as Software Package Data Exchange [SPDX]
   or CycloneDX[CycloneDX12].

   This memo specifies means by which SBOMs can be advertised and
   retrieved.

   The mechanisms specified in this document are meant to satisfy
   several use cases:

   *  A network-layer management system retrieving an SBOM from an IoT
      device as part of its ongoing lifecycle.  Such devices may or may
      not have interfaces available to query SBOM information.

   *  An application-layer management system retrieving an SBOM in order
      to evaluate the posture of an application server of some form.
      These application servers may themselves be containers or
      hypervisors.  Discovery of the topology of a server is beyond the
      scope of this memo.

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   To satisfy these two key use cases, SBOMs may be found in one of
   three ways:

   *  on devices themselves

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

   *  through some form of out-of-band contact with the supplier.

   In the first case, devices will have interfaces that permit direct
   SBOM retrieval.  Examples of these interfaces might be an HTTP, COAP
   or [OpenC2] endpoint for retrieval.  There may also be private
   interfaces as well.

   In the second case, when a device does not have an appropriate
   interface to retrieve an SBOM, but one is directly available from the
   manufacturer, a URI to that information must be discovered.

   In the third case, a supplier may wish to make an SBOM available
   under certain circumstances, and may need to individually evaluate
   requests.  The result of that evaluation might be the SBOM itself or
   a restricted URL or no access.

   To enable application-layer discovery, this memo defines a well-known
   URI [RFC8615].  Management or orchestration tools can query this
   well-known URI to retrieve a system's SBOM.  Further queries may be
   necessary based on the content and structure of a particular SBOM.

   To enable network-layer discovery, particularly for IOT-based
   devices, an extension to Manufacturer Usage Descriptions (MUD) may be
   used[RFC8520].

   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.  Cases Not Addressed

   [ This section to be removed prior to publication ]

   A separate use case may be addressed in future versions of this
   document:

   *  Related to the application layer, software as a service may
      involve multiple backend systems, depending on many factors.  One
      example might be a large cloud-based service that offers

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      spreadsheets, email, and document authoring and management.
      Depending on what service is being used, a different set of back
      end services may in turn be invoking different software that
      should be listed.

   The reason why this use case isn't addressed here is that it may be
   better addressed inline within HTML.  Further discussion is required.

1.2.  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 or establish
   a well-known URI, 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.

1.3.  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.

1.4.  Discussion points

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

   *  Is the model structured correctly?

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

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

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

2.  The .well-known/sbom endpoint set

   If a host offers this service, it will offer the RESTful endpoint
   beginning with "{ORIGIN}/.well-known/sbom/base".

3.  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.  N.B., this schema extension is intended to be used
   wherever it might be appropriate (e.g., not just MUD).

   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 sbom
          +--rw (sbom-type)?
             +--:(cloud)
             |  +--rw sboms* [version-info]
             |     +--rw version-info    string
             |     +--rw sbom-url?       inet:uri
             +--:(local-well-known)
             |  +--rw local-well-known?   empty
             +--:(contact-info)
             |  +--rw contact-uri         inet:uri
             +--:(openc2)
                +--rw openc2-uri          inet:uri

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

   <CODE BEGINS>
   file "ietf-mud-sbom@2021-04-29.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 {

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       prefix mud;
     }

     organization
       "IETF OPSAWG (Ops Area) Working Group";
     contact
       "WG
        Web: http://tools.ietf.org/wg/opsawg/
        WG List: opsawg@ietf.org
        Author: Eliot Lear lear@cisco.com
        Author: Scott Rose scott.rose@nist.gov";
     description
       "This YANG module augments the ietf-mud model to provide for
        reporting of SBOMs.

        Copyright (c) 2020 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 2021-04-29 {
       description
         "Initial proposed standard.";
       reference
         "RFC XXXX: Extension for MUD SBOM";
     }

     grouping mud-sbom-extension {
       description
         "SBOM extension grouping";
       container sbom {
         description
           "container of methods to get an SBOM.";

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         choice sbom-type {
           description
             "SBOM type";
           case cloud {
             list sboms {
               key "version-info";
               description
                 "A list of SBOMs tied to different s/w
                  or h/w versions.";
               leaf version-info {
                 type string;
                 description
                   "The version to which this SBOM refers.";
               }
               leaf sbom-url {
                 type inet:uri;
                 description
                   "A statically located URI.";
               }
             }
           }
           case local-well-known {
             leaf local-well-known {
               type empty;
               description
                 "SBOM information is to be retrieved via
                   https from the host on port 443, at
                   https://{hostname}/.well-known/sbom, where
                   hostname is replaced with the host to which
                   this MUD extension refers.";
             }
           }
           case contact-info {
             leaf contact-uri {
               type inet:uri;
               mandatory true;
               description
                 "This MUST be either a tel, http, https, or
                  mailto uri schema that customers can use to
                  contact someone for SBOM information.";
             }
           }
           case openc2 {
             leaf openc2-uri {
               type inet:uri;
               mandatory true;
               description
                 "A link to the OpenC2 https RESTful

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                    \t mapping.  The OpenC2 protocol is then
                         used to retrieve the SBOM";
             }
           }
         }
       }
     }

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

5.  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.

5.1.  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://frob.example.com/doc/frob2000",
       "model-name": "Frobinator 2000",
       "extensions" : [
          "sbom"
         ],
       "sboms" : { "sbom" : [
         {
            "version-info" : "FrobOS Release 1.1",
            "sbom-url" : "https://frob.example.com/sboms/f20001.1",
         }
       ]
       }
     }
   }

5.2.  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://frob.example.com/doc/frob2000",
       "model-name": "Frobinator 2000",
       "extensions" : [
          "sbom"
         ],
       "sboms" : "sbom" : {
            "sbom-local" : "coaps:///.well-known/sbom",
         }
     }
   }

5.3.  SBOM Obtained from Contact Information

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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://frob.example.com/doc/frob2000",
       "model-name": "Frobinator 2000",
       "extensions" : [
          "sbom"
         ],
       "sboms" : { "sbom" : {
            "contact-uri" : "mailto:sbom-requst@example.com",
         }
       }
     }
   }

5.4.  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://frob.example.com/doc/frob2000",
       "model-name": "Frobinator 2000",
       "extensions" : [
          "sbom"
         ],
       "sboms" : "sbom" : [
         {
            "version-info" : "FrobOS Release 1.1",
            "sbom-url" : "https://frob.example.com/sboms/f20001.1",
         },
       ],
      },
       "from-device-policy": {
         "access-lists": {
           "access-list": [
             {

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               "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.example.com"
                   }
                 },
                 "actions": {
                   "forwarding": "accept"
                 }
               }
             ]
           }
         },
         {
           "name": "mud-96898-v4fr",
           "type": "ipv4-acl-type",
           "aces": {
             "ace": [
               {

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                 "name": "cl0-frdev",
                 "matches": {
                   "ipv4": {
                     "ietf-acldns:dst-dnsname": "cloud.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.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.example.com"
                   }
                 },
                 "actions": {
                   "forwarding": "accept"
                 }
               }

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             ]
           }
         }
       ]
     }
   }

   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.

6.  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 and 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.

   Another risk is a skew in the SBOM listing and the actual software
   inventory of a device/container.  For example, a manufacturer may
   update the SBOM on its server, but an individual device has not be
   upgraded yet.  This may result in an incorrect policy being applied
   to a device.  A unique mapping of a device's firmware version and its
   SBOM can minimize this risk.

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

7.  IANA Considerations

7.1.  MUD Extension

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

     Extension Name: sbom
     Standard reference: This document

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7.2.  Well-Known Prefix

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

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

8.  References

8.1.  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>.

   [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>.

8.2.  Informative References

   [CycloneDX12]
              cylonedx.org, "CycloneDX XML Reference v1.2", May 2020.

   [OpenC2]   Lemire, D., Ed., "Specification for Transfer of OpenC2
              Messages via HTTPS Version 1.0", July 2019,
              <https://docs.oasis-open.org/openc2/open-impl-https/v1.0/
              open-impl-https-v1.0.html>.

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

Appendix A.  Changes from Earlier Versions

   Draft -00:

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   *  Initial revision

Authors' Addresses

   Eliot Lear
   Cisco Systems
   Richtistrasse 7
   CH-8304 Wallisellen
   Switzerland

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

   Scott Rose
   NIST
   100 Bureau Dr
   Gaithersburg MD,  20899
   United States of America

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

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