SBOM YANG model: A YANG Data Model for Reporting Software Bills of Materials (SBOMs) and Vulnerability Information

Internet Engineering Task Force (IETF)                           E. Lear
Request for Comments: 9472                                 Cisco Systems
Category: Standards Track                                        S. Rose
ISSN: 2070-1721                                                     NIST
                                                            October 2023


A YANG Data Model for Reporting Software Bills of Materials (SBOMs) and
                       Vulnerability Information

Abstract

   To improve cybersecurity posture, automation is necessary to locate
   the software a device is using, whether that software has known
   vulnerabilities, and what, if any, recommendations suppliers may
   have.  This memo extends the Manufacturer User Description (MUD) YANG
   schema to provide the locations of software bills of materials
   (SBOMs) and vulnerability information by introducing a transparency
   schema.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9472.

Copyright Notice

   Copyright (c) 2023 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 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
     1.1.  Requirements Language
     1.2.  How This Information Is Retrieved
     1.3.  Formats
   2.  The Well-Known Transparency Endpoint Set
   3.  The mud-transparency Extension
   4.  The mud-sbom Augmentation to the MUD YANG Data Model
   5.  Examples
     5.1.  Without ACLS
     5.2.  SBOM Located on the Device
     5.3.  Further Contact Required
     5.4.  With ACLS
   6.  Security Considerations
   7.  IANA Considerations
     7.1.  MUD Extension
     7.2.  YANG Registration
     7.3.  Well-Known Prefix
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   A number of activities have taken place to improve the visibility of
   what software is running on a system and what vulnerabilities that
   software may have [EO2021].

   Put simply, this memo seeks to answer two classes of questions for
   tens of thousands of devices and a large variety of device types.
   Those questions are as follows:

   *  Is this system susceptible to a particular vulnerability?

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

   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
   intended to facilitate discovery 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 [CycloneDX15].

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

   SBOM and vulnerability information can be used in concert with other
   sources of vulnerability information.  A network management tool
   could discover that a system uses a particular set of software
   components, searches a national vulnerability database to determine
   known vulnerabilities, and applies information provided by the
   manufacturer through this mechanism to produce a vulnerability
   report.  That 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 is because vulnerability
   information changes occur to software updates at different rates.
   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:

   *  A network-layer management system retrieving information from an
      Internet of Things (IoT) device as part of its ongoing life cycle.
      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:

   1.  on the devices themselves

   2.  on a website (e.g., via a URI)

   3.  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
   [RFC9110] or Constrained Application Protocol (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 is discovered through
   interfaces such as MUD via DHCP or bootstrapping and ownership
   transfer mechanisms.

   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, the vulnerability itself, 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.

1.1.  Requirements Language

   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.

1.2.  How This Information Is Retrieved

   Section 4 describes a data model to extend the MUD file format to
   carry SBOM and vulnerability information.  Section 1.5 of [RFC8520]
   describes mechanisms by which devices can emit a URL to point to this
   file.  Additionally, devices can share this URL either through
   documentation or within a QR code on a box.  Section 2 describes a
   well-known URL from which an SBOM could be served from the local
   device.

   Note that vulnerability and SBOM information are 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.

1.3.  Formats

   There are multiple ways to express both SBOMs and vulnerability
   information.  When these are retrieved either from the device or from
   a remote 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 URL, both sbom-url and members
   of the vuln-url list MUST indicate that.  Network management systems
   MUST take note of when the SBOM and vulnerability information are
   accessible via the same resource and not retrieve the resource a
   second time.

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.

3.  The mud-transparency Extension

   We now formally define the mud-transparency extension; this is done
   in two parts.

   First, the extension name "transparency" is listed in the
   "extensions" array of the MUD file.  Note that this schema extension
   is intended to be used wherever it might be appropriate (e.g., not
   just with 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 Data Model

   This YANG module references [RFC6991], [RFC7231], [RFC7252],
   [RFC8520], and [RFC9110].

   <CODE BEGINS> file "ietf-mud-transparency@2023-10-10.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: Common YANG Data Types";
     }
     import ietf-mud {
       prefix mud;
       reference
         "RFC 8520: Manufacturer Usage Description Specification";
     }

     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.

        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.

        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 9472
        (https://www.rfc-editor.org/info/rfc9472);
        see the RFC itself for full legal notices.";

     revision 2023-10-10 {
       description
         "Initial proposed standard.";
       reference
         "RFC 9472: A YANG Data Model for Reporting Software Bills
          of Materials (SBOMs) and Vulnerability Information";
     }

     identity local-type {
       description
         "Base identity for local well-known choices.";
     }

     identity http {
       base mudtx:local-type;
       description
         "Use http (RFC 7231) (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.";
         reference
           "RFC 7231: Hypertext Transfer Protocol (HTTP/1.1):
            Semantics and Content";
     }

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

     identity coap {
       base mudtx:local-type;
       description
         "Use COAP (RFC 7252) (insecure) to retrieve SBOM.  This method
          is NOT RECOMMENDED, although it may be unavoidable
          for certain classes of implementations/deployments.";
         reference
           "RFC 7252: The Constrained Application Protocol (CoAP)";
     }

     identity coaps {
       base mudtx:local-type;
       description
         "Use COAPS (secure) to retrieve SBOM (RFC 7252).";
     }

     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
                 "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 a tel, an http, an https, or
                  a 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 be found inside
              the SBOMs.";
         }
         choice vuln-retrieval-method {
           description
             "How to find vulnerability information.";
           case cloud {
             leaf-list vuln-url {
               type inet:uri;
               description
                 "List of statically located URLs that reference
                  vulnerability information.";
             }
           }
           case vuln-contact-info {
             leaf vuln-contact-uri {
               type inet:uri {
                 pattern '((mailto)|(https?)|(tel)):.*';
               }
               description
                 "This MUST be a tel, an http, an https, or
                  a 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 that the Access
   Control Lists (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.

   {
    "ietf-mud:mud": {
      "mud-version": 1,
      "extensions": [
        "transparency"
      ],
      "mudtx:transparency": {
        sboms: [ {
        "version-info": "1.2",
        "sbom-url": "https://iot.example.com/info/modelX/sbom.json"
        } ],
        "vuln-url" : [
          "https://iotd.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 from the cloud.

   {
    "ietf-mud:mud": {
      "mud-version": 1,
      "extensions": [
        "transparency"
      ],
      "mudtx:transparency": {
        sboms: [ {
        "version-info": "1.2",
        "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": "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"
    }
   }

5.2.  SBOM Located on the Device

   In the next example, the SBOM is located on the device, and there is
   no vulnerability information provided.

   {
     "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 SBOM info from a local source",
       "mfg-name": "Example, Inc.",
       "documentation": "https://iot.example.com/doc/modelX",
       "model-name": "modelX"
     }
   }

   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://iotd.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": "mixed example: SBOM on device, vuln info in cloud",
      "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.

   {
   "ietf-mud:mud": {
   "mud-version": 1,
   "extensions": [
     "transparency"
   ],
   "mudtx:transparency": {
     "contact-info": "https://iot-device.example.com/contact-info.html",
       "vuln-url" : [
         "https://iotd.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://iotd.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": {
          "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"
                  }
                },
                "actions": {
                  "forwarding": "accept"
                }
              }
            ]
          }
        }
      ]
    }
   }

   At this point, the management system can attempt to retrieve the
   SBOM, 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 necessarily intended to be
   accessed via regular network management protocols, such as NETCONF
   [RFC6241] or RESTCONF [RFC8040], and hence the regular security
   considerations for such usage are not considered here.

   Below, we describe protections relating to both discovery and some
   advice on protecting the underlying SBOM and 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 are no means, for instance, to upload an SBOM.
   Additional risks are discussed below and are applicable to all nodes
   within the transparency container.

   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 of these risks or any tampering of a URL:

   *  test any cloud-based URL against a reputation service

   *  provide the administrator an opportunity to approve further
      processing when the authority changes to one not known to be
      reputable

   SBOMs provide an inventory of software.  Knowledge of which specific
   software is loaded on a system can aid an attacker in identifying an
   appropriate exploit for a known vulnerability or guide the
   development of novel exploit against this system.  However, if
   software is available to an attacker, the attacker may 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 to the well-known URL 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 or CoAP
   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 network access controls.

   Vulnerability information is generally made available to such
   databases as NIST's National Vulnerability Database [NISTNVD].  It is
   possible that vendors 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 that information.

7.  IANA Considerations

7.1.  MUD Extension

   IANA has added "transparency" to the "MUD Extensions" registry
   [RFC8520] as follows:

   Value:  transparency
   Reference:  RFC 9472

7.2.  YANG Registration

   IANA has registered the following YANG module in the "YANG Module
   Names" registry [RFC6020]:

   Name:  ietf-mud-transparency
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-mud-transparency
   Maintained by IANA:  N
   Prefix:  mudtx
   Reference:  RFC 9472

   The following URI has been registered in the "IETF XML Registry"
   [RFC3688]:

   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

   IANA has added the following URI suffix to the "Well-Known URIs"
   registry in accordance with [RFC8615]:

   URI Suffix:  sbom
   Change Controller:  IETF
   Reference:  RFC 9472
   Status:  permanent
   Related Information:  See ISO/IEC 5962:2021 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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [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>.

   [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>.

   [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>.

   [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>.

8.2.  Informative References

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

   [CVRF]     Hagen, S., Ed., "CSAF Common Vulnerability Reporting
              Framework (CVRF) Version 1.2", Committee Specification 01,
              September 2017, <https://docs.oasis-open.org/csaf/csaf-
              cvrf/v1.2/csaf-cvrf-v1.2.pdf>.

   [CycloneDX15]
              CycloneDX, "CycloneDX v1.5 JSON Reference", Version 1.5.0,
              <https://cyclonedx.org/docs/1.5/json>.

   [EO2021]   Biden, J., "Executive Order on Improving the Nation's
              Cybersecurity", EO 14028, May 2021.

   [NISTNVD]  NIST, "National Vulnerability Database",
              <https://nvd.nist.gov>.

   [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>.

   [SPDX]     The Linux Foundation, "The Software Package Data Exchange
              (SPDX) Specification", Version 2.3, 2022,
              <https://spdx.github.io/spdx-spec/v2.3/>.

Acknowledgments

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

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