Discovering and Retrieving Software Transparency and Vulnerability Information
draft-ietf-opsawg-sbom-access-15

Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                 S. Rose
Expires: 28 September 2023                                          NIST
                                                           27 March 2023

   Discovering and Retrieving Software Transparency and Vulnerability
                              Information
                    draft-ietf-opsawg-sbom-access-15

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 extends the MUD YANG model to provide the locations of
   software bills of materials (SBOMS) and to vulnerability information.

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 28 September 2023.

Copyright Notice

   Copyright (c) 2023 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  How This Information Is Retrieved . . . . . . . . . . . .   5
     1.2.  Formats . . . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  The well-known transparency endpoint set  . . . . . . . . . .   5
   3.  The mud-transparency extension model extension  . . . . . . .   6
   4.  The mud-sbom augmentation to the MUD YANG model . . . . . . .   6
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Without ACLS  . . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  SBOM Located on the Device  . . . . . . . . . . . . . . .  12
     5.3.  Further contact required. . . . . . . . . . . . . . . . .  12
     5.4.  With ACLS . . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  MUD Extension . . . . . . . . . . . . . . . . . . . . . .  17
     7.2.  YANG Registration . . . . . . . . . . . . . . . . . . . .  17
     7.3.  Well-Known Prefix . . . . . . . . . . . . . . . . . . . .  17
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     9.2.  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[EO2021].

   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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   This memo doesn't specify the format of this information, but rather
   only how to locate and retrieve these objects.  That is, the model is
   a discovery mechanism, and on its own provides no access to the
   underlying data.

   Software bills of materials (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
   administrators 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 SBOM formats 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 does not specify how vulnerability information may be
   retrieved directly from the endpoint.  That's because vulnerability
   information changes occur at different rates to software updates.
   However, some SBOM formats may also contain vulnerability
   information.

   SBOMs and vulnerability information are 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.  Moreover, other
   MUD features, such as access controls, needn't be present.

   The mechanisms specified in this document are meant to address two
   use cases:

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   *  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.

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

   *  on devices themselves

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

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

   Using the first method, devices will have interfaces that permit
   direct retrieval.  Examples of these interfaces might be an HTTP
   [RFC7231],[RFC9110], or COAP [RFC7252] endpoint for retrieval.  There
   may also be private interfaces as well.

   Using the second method, 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.

   Using the third method, 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 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.

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1.1.  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
   either in 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.  MUD's cache-validity node provides a way for
   manufacturers to control how often tooling should check for those
   changes through the cache-validity node.

1.2.  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.

   If multiple SBOMs are intended to be supported in the same file, the
   media type should properly reflect that.  For example, one might make
   use of application/{someformat}+json-seq.  It is left to those
   supporting those formats to make the appropriate registrations in
   this case.

   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.

2.  The well-known transparency endpoint set

   A well-known endpoint is defined:

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

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

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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:

   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?   identityref
          |  +--:(sbom-contact-info)
          |     +--rw sbom-contact-uri?        inet:uri
          +--rw sbom-archive-list?             inet:uri
          +--rw (vuln-retrieval-method)?
             +--:(cloud)
             |  +--rw vuln-url?                inet:uri
             +--:(vuln-contact-info)
                +--rw vuln-contact-uri?        inet:uri

   See [RFC8340] for a description of YANG trees.

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

   <CODE BEGINS>
   file "ietf-mud-transparency@2023-01-12.yang"
   module ietf-mud-transparency {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-mud-transparency";
     prefix mudtx;

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991";
     }

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     import ietf-mud {
       prefix mud;
       reference
         "RFC 8520";
     }

     organization
       "IETF OPSAWG (Ops Area) Working Group";
     contact
       "WG Web: https://datatracker.ietf.org/wg/opsawg/
        WG List: opsawg@ietf.org

        Editor: Eliot Lear lear@cisco.com
        Editor: Scott Rose scott.rose@nist.gov";
     description
       "This YANG module augments the ietf-mud model to provide for
        reporting of SBOMs and vulnerability information.

        Copyright (c) 2023 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 Revised 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 2023-01-12 {
       description
         "Initial proposed standard.";
       reference
         "RFC XXXX: Discovering and Retrieving Software Transparency
          and Vulnerability Information";
     }

     identity local-type {
       description

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         "Base identity for local-well-known choices";
     }

     identity http {
       base mudtx:local-type;
       description
         "Use http[RFC7231] (insecure) to retrieve SBOM information.
           This method is NOT RECOMMENDED, but may be unavoidable for
           certain classes of deployment, where TLS has not or
           cannot be implemented";
     }

     identity https {
       base mudtx:local-type;
       description
         "Use https (secure) to retrieve SBOM information. See
          RFC 9110.";
     }

     identity coap {
       base mudtx:local-type;
       description
         "Use COAP [RFC7252] (insecure) to retrieve SBOM.  This method
          is NOT RECOMMENDED, although it may be unavoidable
          for certain classes of implementations/deployments.";
     }

     identity coaps {
       base mudtx:local-type;
       description
         "Use COAPS (secure) to retrieve SBOM [RFC7252]";
     }

     grouping transparency-extension {
       description
         "This grouping provides a means to describe the location of
          software bills of material and vulnerability descriptions.";
       container transparency {
         description
           "Container of methods to get SBOMs and vulnerability
            information.";
         choice sbom-retrieval-method {
           description
             "How to find SBOM information";
           case cloud {
             list sboms {
               key "version-info";
               description

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                 "A list of SBOMs tied to different software
                  or hardware versions.";
               leaf version-info {
                 type string;
                 description
                   "The version to which this SBOM refers.";
               }
               leaf sbom-url {
                 type inet:uri {
                   pattern '((coaps?)|(https?)):.*';
                 }
                 description
                   "A statically located URL.";
               }
             }
           }
           case local-well-known {
             leaf sbom-local-well-known {
               type identityref {
                 base mudtx:local-type;
               }
               description
                 "Which communication protocol to choose.";
             }
           }
           case sbom-contact-info {
             leaf sbom-contact-uri {
               type inet:uri {
                 pattern '((mailto)|(https?)|(tel)):.*';
               }
               description
                 "This MUST be either a tel, http, https, or
                  mailto uri schema that customers can use to
                  contact someone for SBOM information.";
             }
           }
         }
         leaf sbom-archive-list {
           type inet:uri;
           description
             "This URI returns a JSON list of URLs that consist of
              SBOMs that were previously published for this
              device.  Publication dates can found inside
              the SBOMs.";
         }
         choice vuln-retrieval-method {
           description
             "How to find vulnerability information";

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           case cloud {
             leaf vuln-url {
               type inet:uri;
               description
                 "A statically located URL that references
                 vulnerability information";
             }
           }
           case vuln-contact-info {
             leaf vuln-contact-uri {
               type inet:uri {
                  pattern '((mailto)|(https?)|(tel)):.*';
               }
               description
                 "This MUST be either a tel, http, https, or
                  mailto uri schema that customers can use to
                  contact someone for vulnerability information.";
             }
           }
         }
       }
     }

     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"
      ],
      "mudtx:transparency": {
        "sbom-local-well-known": "https",
        "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": "2022-01-05T13:29:12+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.

  {
    "ietf-mud:mud": {
      "mud-version": 1,
      "extensions": [
        "transparency"
      ],
      "mudtx:transparency": {
        "sbom-local-well-known": "https"
      },
      "mud-url": "https://iot.example.com/modelX.json",
      "mud-signature": "https://iot.example.com/modelX.p7s",
      "last-update": "2022-01-05T13:29:47+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"
    }
  }

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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.

{
  "ietf-mud:mud": {
    "mud-version": 1,
    "extensions": [
      "transparency"
    ],
    "mudtx: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": "2022-01-05T13:25:14+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"
   ],
   "ietf-mud-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"
      ],
      "mudtx:transparency": {
        "sbom-local-well-known": "https",
        "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": "2022-01-05T13:30:31+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",
      "from-device-policy": {
        "access-lists": {

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          "access-list": [
            {
              "name": "mud-65443-v4fr"
            }
          ]
        }
      },
      "to-device-policy": {
        "access-lists": {
          "access-list": [
            {
              "name": "mud-65443-v4to"
            }
          ]
        }
      }
    },
    "ietf-access-control-list:acls": {
      "acl": [
        {
          "name": "mud-65443-v4to",
          "type": "ipv4-acl-type",
          "aces": {
            "ace": [
              {
                "name": "cl0-todev",
                "matches": {
                  "ipv4": {
                    "ietf-acldns:src-dnsname": "iotserver.example.com"
                  }
                },
                "actions": {
                  "forwarding": "accept"
                }
              }
            ]
          }
        },
        {
          "name": "mud-65443-v4fr",
          "type": "ipv4-acl-type",
          "aces": {
            "ace": [
              {
                "name": "cl0-frdev",
                "matches": {
                  "ipv4": {
                    "ietf-acldns:dst-dnsname": "iotserver.example.com"

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                  }
                },
                "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

   This document describes a schema for discovering the location of
   information relating to software transparency, and does not specify
   the access model for the information itself.  In particular, the YANG
   module specified in this document is not necessarly intended to be
   accessed via regular network management protocols, such as the
   NETCONF [RFC6241] or RESTCONF [RFC8040], and hence the regular
   security considerations for such usage are not considered here.

   We describe below protections relating to both discovery and some
   advice on protecting the underlying SBOM/vulnerability information.

   The model specifies both encrypted and unencrypted means to retrieve
   information.  This is a matter of pragmatism.  Unencrypted
   communications allow for manipulation of information being retrieved.
   Therefore, it is RECOMMENDED that implementations offer a means to
   configure endpoints so that they may make use of TLS or DTLS.

   The ietf-mud-transparency module has no operational impact on the
   element itself, and is used to discover state information that may be
   available on or off the element.  In as much as the module itself is
   made writeable, this only indicates a change in how to retrieve read-
   only elements.  There is no means, for instance, to upload an SBOM.
   Additional risks are discussed below, and are applicable to all nodes
   within the transparency container.

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   If an attacker modifies the elements, they may misdirect automation
   to retrieve a different set of URLs than was intended by the
   designer.  This in turn leads to two specific sets of risks:

   *  the information retrieved would be false.

   *  the URLs themselves point to malware.

   To address either risk, any change in a URL, and in particular to the
   authority section, should be treated with some suspicion.  One
   mitigation would be to test any cloud-based URL against a reputation
   service.

   SBOMs provide an inventory of software.  If software is available to
   an attacker, the attacker may well already be able to derive this
   very same software inventory.  When this information resides on the
   endpoint itself, the endpoint SHOULD NOT provide unrestricted access
   by default.  Other servers that offer the data MAY restrict access to
   SBOM information using appropriate authorization semantics within
   HTTP.  One way to do this would be to issue a certificate to the
   client for this purpose after a registration process has taken place.
   Another approach would involve the use of OAUTH in combination.  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.

   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 been
   upgraded yet.  This may result in an incorrect policy being applied
   to a device.  A unique mapping of a device's software version and its
   SBOM can minimize this risk.

   To further mitigate attacks against a device, manufacturers SHOULD
   recommend access controls.

   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 authorization SHOULD
   be applied to the vulnerability resource.

7.  IANA Considerations

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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.  YANG Registration

   The following YANG module should be registered in the "YANG Module
   Names" registry:

      Name: ietf-mud
      URN: urn:ietf:params:xml:ns:yang:ietf-mud-transparency
      Prefix: mudtx
      Registrant contact: The IESG
      Reference: This memo

   The following XML registration is requested:

      URI: urn:ietf:params:xml:ns:yang:ietf-mud-transparency
      Registrant Contact: IESG
      XML: None.  Namespace URIs do not represent an XML specification.

7.3.  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 5962:2021 and SPDX.org

8.  Acknowledgments

   Thanks to Russ Housley, Dick Brooks, Tom Petch, Nicolas Comstedt, who
   provided review comments.

9.  References

9.1.  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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   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

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

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [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>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [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>.

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9.2.  Informative References

   [CSAF]     Rock, L., Ed., Hagen, S., Ed., and T. Schmidt, Ed.,
              "Common Security Advisory Framework Version 2.0", November
              2022, <https://docs.oasis-open.org/csaf/csaf/v2.0/csaf-
              v2.0.html>.

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

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

   [EO2021]   Biden, J., "Executive Order 14028, Improving the Nations
              Cybersecurity", May 2021.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/info/rfc9110>.

   [SPDX]     The Linux Foundation, "SPDX Specification V2.3", 2022,
              <https://spdx.github.io/spdx-spec/v2.3/>.

Appendix A.  Changes from Earlier Versions

   Draft -04: * Address review comments

   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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