Discovering And Accessing Software Bills of MaterialsCisco SystemsRichtistrasse 7WallisellenCH-8304Switzerland+41 44 878 9200lear@cisco.comNIST100 Bureau DrGaithersburg MD20899USA+1 301-975-8439scott.rose@nist.govInternet-DraftSoftware bills of materials (SBOMs) are formal descriptions of what
pieces of software are included in a product. This memo specifies a
different means for SBOMs to be retrieved.Software bills of material (SBOMs) are descriptions of what software,
including versioning and dependencies, a device contains. There
are different SBOM formats such as Software Package Data Exchange
, Software Identity Tags , or CycloneDX.This memo specifies means by which SBOMs can be advertised and retrieved.The mechanisms specified in this document are meant to satisfy several
use cases:An application-layer management system retrieving an SBOM in
order to evaluate the posture of an application server of some
form. These application servers may themselves be containers or
hypervisors. Discovery of the topology of a server is beyond the
scope of this memo.A network-layer management system retrieving an SBOM from an IoT
device as part of its ongoing lifecycle. Such devices may or may not
have interfaces available to query SBOM information.To satisfy these two key use cases, SBOMs may be found in one of three
ways:on devices themselveson a web site (e.g., via URI)through some form of out-of-band contact with the supplier.In the first case, devices will have interfaces that permit direct
SBOM retrieval. Examples of these interfaces might be an
HTTP or COAP endpoint for retrieval. There may also be private
interfaces as well.In the second case, when a device does not have an appropriate
interface to retrieve an SBOM, but one is directly available from the
manufacturer, a URI to that information must be discovered.In the third case, a supplier may wish to make an SBOM available under
certain circumstances, and may need to individually evaluate requests.
The result of that evaluation might be the SBOM itself or a restricted
URL or no access.To enable application-layer discovery, this memo defines a well-known
URI . Management or orchestration tools can query this
well-known URI to retrieve a system’s SBOM. Further queries may be
necessary based on the content and structure of a particular SBOM.To enable network-layer discovery, particularly for IOT-based devices,
an extension to Manufacturer Usage Descriptions (MUD) may be
used.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 when, and only when, they
appear in all capitals, as shown here.SBOMs are used for numerous purposes, including vulnerability
assessment, license management, and inventory management. This memo
provides means for either automated or semi-automated collection of
that information. For devices that can output a MUD URL or establish
a well-known URI, the mechanism may be highly automated. For devices
that have a MUD URL in either their documentation or within a QR code
on a box, the mechanism is semi-automated (someone has to scan the QR
code or enter the URL).Note that SBOMs may change more frequently than access control
requirements. A change to software does not necessarily mean a change
to control channels that are used. Therefore, it is important to
retrieve the MUD file as suggested by the manufacturer in the
cache-validity period. In many cases, only the SBOM list will have
been updated.There are multiple ways to express an SBOM. When these are retrieved
either directly from the device or directly from a web server, tools
will need to observe the content-type header to determine precisely
which format is being transmitted. Because IoT devices in particular
have limited capabilities, use of a specific Accept: header in HTTP
or the Accept Option in CoAP is NOT RECOMMENDED. Instead, backend
tooling MUST silently discard SBOM information sent with a media type
that is not understood.The following is discussion to be removed at time of RFC publication.Is the model structured correctly?Are there other retrieval mechanisms that need to be specified?Do we need to be more specific in how to authenticate and retrieve
SBOMs?What are the implications if the MUD URL is an extension in a certificate
(e.g. an IDevID cert)?We now formally define this extension. This is done in two parts.
First, the extension name “sbom” is listed in the
“extensions” array of the MUD file.Second, the “mud” container is augmented with a list of SBOM sources.This is done as follows:In this example MUD file that uses a cloud service, the Frobinator
presents a location of the SBOM in a URL. Note, the ACLs in a MUD
file are NOT required, although they are a very good idea for IP-based
devices. The first MUD file demonstrates how to get the SBOM without
ACLs, and the second has ACLs.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.SBOMs provide an inventory of software. If firmware is available to
an attacker, the attacker may well already be able to derive this very
same software inventory. Manufacturers MAY restrict access to SBOM
information using appropriate authorization semantics within HTTP. In
particular, if a system attempts to retrieve an SBOM via HTTP, if the
client is not authorized, the server MUST produce an appropriate
error, with instructions on how to register a particular client. One
example may be to issue a certificate to the client for this purpose
after a registration process has taken place. Another example would
involve the use of OAUTH in combination with a federations of SBOM
servers.Another risk is a skew in the SBOM listing and the actual software
inventory of a device/container. For example, a manufactuer may update
the SBOM on its server, but an individual device has not be upgraded yet.
This may result in an incorrect policy being applied to a device. A unique mapping of a device’s firmware version and its SBOM can
minimize this risk.To further mitigate attacks against a device, manufacturers SHOULD
recommend access controls through the normal MUD mechanism.The IANA is requested to add “controller-candidate” to the MUD
extensions registry as follows:The following well known URI is requested in accordance with
:Common YANG Data TypesThis document introduces a collection of common data types to be used with the YANG data modeling language. This document obsoletes RFC 6021.Manufacturer Usage Description SpecificationThis memo specifies a component-based architecture for Manufacturer Usage Descriptions (MUDs). The goal of MUD is to provide a means for end devices to signal to the network what sort of access and network functionality they require to properly function. The initial focus is on access control. Later work can delve into other aspects.This memo specifies two YANG modules, IPv4 and IPv6 DHCP options, a Link Layer Discovery Protocol (LLDP) TLV, a URL, an X.509 certificate extension, and a means to sign and verify the descriptions.Key words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Well-Known Uniform Resource Identifiers (URIs)This memo defines a path prefix for "well-known locations", "/.well-known/", in selected Uniform Resource Identifier (URI) schemes.In doing so, it obsoletes RFC 5785 and updates the URI schemes defined in RFC 7230 to reserve that space. It also updates RFC 7595 to track URI schemes that support well-known URIs in their registry.SPDX Specification 2.1The Linux FoundationInformation technology — IT asset management — Part 2: Software identification tagISO/IECCycloneDX XML Reference v1.2cylonedx.orgDraft -00:Initial revision