wdiff rfc9472v1.txt rfc9472.txt

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

Discovering and Retrieving

A YANG Data Model for Reporting Software Transparency 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.

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
1.2.
1.3. Formats
2. The Well-Known Transparency Endpoint Set
3. The mud-transparency Extension Model 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 been working taken place to improve the visibility to 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 vulnerable 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 [CycloneDX12]. [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.

1.1.

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.

1.2.

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
retrieving this information
MUST take note that of when the identical SBOM and vulnerability information are
accessible via the same resource is being retrieved rather than retrieving it twice. 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 Content-Type provided.

3. The mud-transparency Extension Model 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. N.B., 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@2023-09-08.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.

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 2023-09-08 {
description
"Initial proposed standard.";
reference
"RFC 9472: Discovering and Retrieving A YANG Data Model for Reporting Software Transparency 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", "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 only 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.

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"
],
"ietf-mud-transparency: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 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 risk, of these risks or any change in tampering of a URL, and in particular to the
authority section, two approaches may be used: 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 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>.

[CycloneDX12]

[CycloneDX15]
CycloneDX, "CycloneDX v1.2 XML v1.5 JSON Reference", Version 1.2.1,
<https://cyclonedx.org/docs/1.2/xml>. 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