Discovering and Retrieving Software Transparency and Vulnerability Information
draft-ietf-opsawg-sbom-access-02

Document Type Active Internet-Draft (opsawg WG)
Authors Eliot Lear  , Scott Rose 
Last updated 2021-07-09
Replaces draft-lear-opsawg-sbom-access
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Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                 S. Rose
Expires: 10 January 2022                                            NIST
                                                             9 July 2021

   Discovering and Retrieving Software Transparency and Vulnerability
                              Information
                    draft-ietf-opsawg-sbom-access-02

Abstract

   To improve cybersecurity posture, automation is necessary to locate
   what software is running on a device, whether that software has known
   vulnerabilities, and what, if any recommendations suppliers may have.
   This memo specifies a model to provide access this information.  It
   may optionally be discovered through manufacturer usage descriptions.

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 10 January 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Cases Not Addressed . . . . . . . . . . . . . . . . . . .   4
     1.2.  How This Information Is Retrieved . . . . . . . . . . . .   5
     1.3.  Formats . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.4.  Discussion points . . . . . . . . . . . . . . . . . . . .   5
   2.  The .well-known/transparency endpoint set . . . . . . . . . .   6
   3.  The mud-transparency extension model extension  . . . . . . .   6
   4.  The mud-sbom augmentation to the MUD YANG model . . . . . . .   7
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Without ACLS  . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  SBOM Located on the Device  . . . . . . . . . . . . . . .  13
     5.3.  Further contact required. . . . . . . . . . . . . . . . .  14
     5.4.  With ACLS . . . . . . . . . . . . . . . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
     7.1.  MUD Extension . . . . . . . . . . . . . . . . . . . . . .  18
     7.2.  Well-Known Prefix . . . . . . . . . . . . . . . . . . . .  18
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Appendix A.  Changes from Earlier Versions  . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   A number of activities have been working to improve visibility to
   what software is running on a system, and what vulnerabilities that
   software may have.

   Put simply, we seek to answer two classes of questions *at scale*:

   *  Is this system vulnerable to a particular vulnerability?

   *  Which devices in a particular environment contain vulnerabilities
      that require some action?

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   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].

   System vulnerabilities may similarly be described using several data
   formats, including the aforementioned CycloneDX, Common Vulnerability
   Reporting Framework [CVRF], the Common Security Advisory Format
   [CSAF].  This information is typically used to report to customers
   the state of a system.

   These two classes of information can be used in concert.  For
   instance, a network management tool may discover that a system makes
   use of a particular software component that has a known
   vulnerability, and a vulnerability report may be used to indicate
   what if any versions of software correct that vulnerability, or
   whether the system exercises the vulnerable code at all.

   Both classes of information elements are optional under the model
   specified in this memo.  One can provide only an SBOM, only
   vulnerability information, or both an SBOM and vulnerability
   information.

   Note that SBOMs may also carry other information, the most common
   being any licensing terms.  Because this specification is neutral
   regarding content, it is left for format developers such as the Linux
   Foundation, OASIS, and ISO to decide what attributes they will
   support.

   This memo specifies means by which both SBOMs and vulnerability
   information can be advertised and retrieved through the use of a YANG
   augmentation of the Manufacturer User Description (MUD) model
   [RFC8520].  Note that the schema creates a grouping that can also be
   used independently of MUD.

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

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

   *  An application-layer management system retrieving vulnerability or
      SBOM information 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, objects 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
   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
   retrieval interface, 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 or
   vulnerability information available under certain circumstances, and
   may need to individually evaluate requests.  The result of that
   evaluation might be the SBOM or vulnerability 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 or vulnerability
   information.  Further queries may be necessary based on the content
   and structure of the response.

   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:

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   *  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
      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 Retrieved

   For devices that can emit a URL or can establish a well-known URI,
   the mechanism may be highly automated.  For devices that have a 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 vulnerability and SBOM information is likely to change at
   different rates.  The MUD semantics provide a way for manufacturers
   to control how often tooling should check for those changes through
   the cache-validity node.

1.3.  Formats

   There are multiple ways to express both SBOMs and vulnerability
   information.  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 is
   encouraged to support all known formats, and SHOULD silently discard
   SBOM information sent with a media type that is not understood.

   Some formats may support both vulnerability and software inventory
   information.  When both vulnerability and software inventory
   information is available from the same location, both sbom and vuln
   nodes MUST indicate that.  Network management systems retrieving this
   information MUST take note that the identical resource is being
   retrieved rather than retrieving it twice.

1.4.  Discussion points

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

   *  Is the model structured correctly?

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

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

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

2.  The .well-known/transparency endpoint set

   Three well known endpoints are defined:

   *  "/.well-known/sbom" retrieves an SBOM.

   *  "/.well-known/vuln" retrieves vulnerability information.

   *  "/.well-known/openc2" is the HTTPS binding to OpenC2.

   As discussed previously, the precise format of a response is based on
   the Content-type provided.

3.  The mud-transparency extension model extension

   We now formally define this extension.  This is done in two parts.
   First, the extension name "transparency" 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:

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   module: ietf-mud-transparency

     augment /mud:mud:
       +--rw transparency
          +--rw (sbom-retrieval-method)?
          |  +--:(cloud)
          |  |  +--rw sboms* [version-info]
          |  |     +--rw version-info    string
          |  |     +--rw sbom-url?       inet:uri
          |  +--:(local-well-known)
          |  |  +--rw sbom-local-well-known?   enumeration
          |  +--:(sbom-contact-info)
          |     +--rw sbom-contact-uri         inet:uri
          +--rw (vuln-retrieval-method)?
             +--:(cloud)
             |  +--rw vuln-url?                inet:uri
             +--:(vuln-local-well-known)
             |  +--rw vuln-local-well-known?   enumeration
             +--:(vuln-contact-info)
                +--rw contact-uri              inet:uri

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

   <CODE BEGINS>
   file "ietf-mud-transparency@2021-07-06.yang"
   module ietf-mud-transparency {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-mud-transparency";
     prefix mud-transparency;

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

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        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 2021-07-06 {
       description
         "Initial proposed standard.";
       reference
         "RFC XXXX: Extension for software transparency";
     }

     grouping transparency-extension {
       description
         "Transparency extension grouping";
       container transparency {
         description
           "container of methods to get an SBOM.";
         choice sbom-retrieval-method {
           description
             "How to find SBOM information";
           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 {

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                 type inet:uri;
                 description
                   "A statically located URI.";
               }
             }
           }
           case local-well-known {
             leaf sbom-local-well-known {
               type enumeration {
                 enum http {
                   description
                     "Use http (insecure) to retrieve
                      SBOM information.";
                 }
                 enum https {
                   description
                     "Use https (secure) to retrieve SBOM information.";
                 }
                 enum coap {
                   description
                     "Use COAP (insecure) to retrieve SBOM";
                 }
                 enum coaps {
                   description
                     "Use COAPS (secure) to retrieve SBOM";
                 }
                 enum openc2 {
                   description
                     "Use OpenC2 endpoint.
                      This is https://{host}/.well-known/openc2";
                 }
               }
               description
                 "Which communication protocol to choose.";
             }
           }
           case sbom-contact-info {
             leaf sbom-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.";
             }
           }
         }
         choice vuln-retrieval-method {

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           description
             "How to find vulnerability information";
           case cloud {
             leaf vuln-url {
               type inet:uri;
               description
                 "A statically located URL.";
             }
           }
           case vuln-local-well-known {
             leaf vuln-local-well-known {
               type enumeration {
                 enum http {
                   description
                     "Use http (insecure) to retrieve vulnerability
                      information.";
                 }
                 enum https {
                   description
                     "Use https to retrieve vulnerability information.";
                 }
                 enum coap {
                   description
                     "Use COAP (insecure) to retrieve vulnerability
                      information";
                 }
                 enum coaps {
                   description
                     "Use COAPS to retrieve vulnerability information";
                 }
                 enum openc2 {
                   description
                     "Use OpenC2 endpoint.
                      This is https://{host}/.well-known/openc2";
                 }
               }
               description
                 "What communication protocol to use.";
             }
           }
           case vuln-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 vulnerability information.";

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             }
           }
         }
       }
     }

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

5.  Examples

   In this example MUD file that uses a cloud service, the modelX
   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.

5.1.  Without ACLS

   This first MUD file demonstrates how to get SBOM and vulnerability
   information without ACLs.

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  {
    "ietf-mud:mud": {
      "mud-version": 1,
      "extensions": [
        "transparency"
      ],
      "transparency": {
        "sboms": [
          {
            "version-info": "ExOS1.1",
            "sbom-url": "https://iot.example.com/info/modelX/sbom.json"
          }
        ],
        "vuln-url": "https://iot.example.com/info/modelX/csaf.json"
      },
      "mud-url": "https://iot.example.com/modelX.json",
      "mud-signature": "https://iot.example.com/modelX.p7s",
      "last-update": "2021-07-09T05:57:58+00:00",
      "cache-validity": 48,
      "is-supported": true,
      "systeminfo": "retrieving vuln and SBOM info via a cloud service",
      "mfg-name": "Example, Inc.",
      "documentation": "https://iot.example.com/doc/modelX",
      "model-name": "modelX"
    }
  }

   The second example demonstrates that just SBOM information is
   included.

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  {
    "ietf-mud:mud": {
      "mud-version": 1,
      "extensions": [
        "transparency"
      ],
      "transparency": {
        "sboms": [
          {
            "version-info": "ExOS1.1",
            "sbom-url": "https://iot.example.com/info/modelX/sbom.json"
          }
        ]
      },
      "mud-url": "https://iot.example.com/modelX.json",
      "mud-signature": "https://iot.example.com/modelX.p7s",
      "last-update": "2021-07-09T06:03:21+00:00",
      "cache-validity": 48,
      "is-supported": true,
      "systeminfo": "retrieving vuln and SBOM info via a cloud service",
      "mfg-name": "Example, Inc.",
      "documentation": "https://iot.example.com/doc/modelX",
      "model-name": "modelX"
    }
  }

5.2.  SBOM Located on the Device

   In this example, the SBOM is retrieved from the device, while
   vulnerability information is available from the cloud.  This is
   likely a common case, because vendors may learn of vulnerability
   information more frequently than they update software.

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 {
  "ietf-mud:mud": {
    "mud-version": 1,
    "extensions": [
      "ol",
      "transparency"
    ],
    "ol": {
      "owners": [
        "Copyright (c) Example, Inc. 2021. All Rights Reserved"
      ],
      "spdx-tag": "0BSD"
    },
    "transparency": {
      "sbom-local-well-known": "https",
      "vuln-url": "https://iot-device.example.com/info/modelX/csaf.json"
    },
    "mud-url": "https://iot-device.example.com/modelX.json",
    "mud-signature": "https://iot-device.example.com/modelX.p7s",
    "last-update": "2021-07-09T06:06:13+00:00",
    "cache-validity": 48,
    "is-supported": true,
    "systeminfo": "retrieving vuln and SBOM info via a cloud service",
    "mfg-name": "Example, Inc.",
    "documentation": "https://iot-device.example.com/doc/modelX",
    "model-name": "modelX"
  }
 }

5.3.  Further contact required.

   In this example, the network manager must take further steps to
   retrieve SBOM information.  Vulnerability information is still
   available.

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 {
  "ietf-mud:mud": {
   "mud-version": 1,
   "extensions": [
     "transparency"
   ],
   "transparency": {
     "contact-info": "https://iot-device.example.com/contact-info.html",
     "vuln-url": "https://iot-device.example.com/info/modelX/csaf.json"
   },
   "mud-url": "https://iot-device.example.com/modelX.json",
   "mud-signature": "https://iot-device.example.com/modelX.p7s",
   "last-update": "2021-07-09T06:16:42+00:00",
   "cache-validity": 48,
   "is-supported": true,
   "systeminfo": "retrieving vuln and SBOM info via a cloud service",
   "mfg-name": "Example, Inc.",
   "documentation": "https://iot-device.example.com/doc/modelX",
   "model-name": "modelX"
  }
 }

5.4.  With ACLS

   Finally, here is a complete example where the device provides SBOM
   and vulnerability information, as well as access-control information.

  {
    "ietf-mud:mud": {
      "mud-version": 1,
      "extensions": [
        "transparency"
      ],
      "transparency": {
        "sboms": [
          {
            "version-info": "ExOS1.1",
            "sbom-url": "https://iot.example.com/info/modelX/sbom.json"
          }
        ],
        "vuln-url": "https://iot.example.com/info/modelX/csaf.json"
      },
      "mud-url": "https://iot.example.com/modelX.json",
      "mud-signature": "https://iot.example.com/modelX.p7s",
      "last-update": "2021-07-09T06:19:39+00:00",
      "cache-validity": 48,
      "is-supported": true,
      "systeminfo": "retrieving vuln and SBOM info via a cloud service",

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      "mfg-name": "Example, Inc.",
      "documentation": "https://iot.example.com/doc/modelX",
      "model-name": "modelX",
      "from-device-policy": {
        "access-lists": {
          "access-list": [
            {
              "name": "mud-15060-v4fr"
            }
          ]
        }
      },
      "to-device-policy": {
        "access-lists": {
          "access-list": [
            {
              "name": "mud-15060-v4to"
            }
          ]
        }
      }
    },
    "ietf-access-control-list:acls": {
      "acl": [
        {
          "name": "mud-15060-v4to",
          "type": "ipv4-acl-type",
          "aces": {
            "ace": [
              {
                "name": "cl0-todev",
                "matches": {
                  "ipv4": {
                    "ietf-acldns:src-dnsname": "cloud.example.com"
                  }
                },
                "actions": {
                  "forwarding": "accept"
                }
              }
            ]
          }
        },
        {
          "name": "mud-15060-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"
                }
              }
            ]
          }
        }
      ]
    }
  }

   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, independently repeat the
   process for vulnerability information, and apply ACLs, as
   appropriate.

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.

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   Vulnerability information is generally made available to such
   databases as NIST's National Vulnerability Database.  It is possible
   that vendor may wish to release information early to some customers.
   We do not discuss here whether that is a good idea, but if it is
   employed, then appropriate access controls and authoration would be
   applied to the vulnerability resource.

7.  IANA Considerations

7.1.  MUD Extension

   The IANA is requested to add "transparency" to the MUD extensions
   registry as follows:

     Extension Name: transparency
     Standard reference: This document

7.2.  Well-Known Prefix

   The following well known URIs are 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

     URI suffix: "openc2"
     Change controller: "IETF"
     Specification document: This memo
     Related information:  OpenC2 Project

     URI suffix: "vuln"
     Change controller: "IETF"
     Specification document: This memo
     Related information:  OASIS.ORG's CSAF project

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>.

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   [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

   [CSAF]     OASIS, "Common Security Advisory Format", July 2021,
              <https://github.com/oasis-tcs/csaf>.

   [CVRF]     Santos, O., Ed., "Common Vulnerability Reporting Framework
              (CVRF) Version 1.2", September 2017, <http://docs.oasis-
              open.org/csaf/csaf-cvrf/v1.2/csaf-cvrf-v1.2.pdf>.

   [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 -02:

   *  include vulnerability information

   Draft -01:

   *  some modest changes

   Draft -00:

   *  Initial revision

Authors' Addresses

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   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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