Internet DRAFT - draft-lear-opsawg-sbom-access
draft-lear-opsawg-sbom-access
Network Working Group E. Lear
Internet-Draft Cisco Systems
Intended status: Standards Track S. Rose
Expires: April 16, 2021 NIST
October 13, 2020
Discovering And Accessing Software Bills of Materials
draft-lear-opsawg-sbom-access-00
Abstract
Software 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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 16, 2021.
Copyright Notice
Copyright (c) 2020 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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. How This Information Is Used . . . . . . . . . . . . . . 3
1.2. SBOM formats . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Discussion points . . . . . . . . . . . . . . . . . . . . 4
2. The mud-sbom extension model extension . . . . . . . . . . . 4
3. The mud-sbom augmentation to the MUD YANG model . . . . . . . 5
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Without ACLS . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Located on the Device . . . . . . . . . . . . . . . . . . 8
4.3. SBOM Obtained from Contact Information . . . . . . . . . 9
4.4. With ACLS . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6.1. MUD Extension . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Well-Known Prefix . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Changes from Earlier Versions . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Software bills of material (SBOMs) are descriptions of what software,
including versioning and dependencies, a device contains. There are
different SBOM formats such as Software Package Data Exchange [SPDX],
Software Identity Tags [SWID], or CycloneDX[CycloneDX12].
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:
o 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.
o 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:
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o on devices themselves
o on a web site (e.g., via URI)
o 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 [RFC8615]. 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[RFC8520].
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. How This Information Is Used
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
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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.
1.2. SBOM formats
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.
1.3. Discussion points
The following is discussion to be removed at time of RFC publication.
o Is the model structured correctly?
o Are there other retrieval mechanisms that need to be specified?
o Do we need to be more specific in how to authenticate and retrieve
SBOMs?
o What are the implications if the MUD URL is an extension in a
certificate (e.g. an IDevID cert)?
2. The mud-sbom extension model extension
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:
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module: ietf-mud-sbom
augment /mud:mud:
+--rw sboms* [version-info]
+--rw version-info string
+--rw (sbom-type)?
+--:(url)
| +--rw sbom-url? inet:uri
+--:(local-uri)
| +--rw sbom-local* enumeration
+--:(contact-info)
+--rw contact-uri? inet:uri
3. The mud-sbom augmentation to the MUD YANG model
<CODE BEGINS>file "ietf-mud-sbom@2020-03-06.yang"
module ietf-mud-sbom {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-mud-sbom";
prefix mud-sbom;
import ietf-inet-types {
prefix inet;
}
import ietf-mud {
prefix mud;
}
organization
"IETF OPSAWG (Ops Area) Working Group";
contact
"WG
Web: http://tools.ietf.org/wg/opsawg/
WG List: opsawg@ietf.org
Author: Eliot Lear lear@cisco.com ";
description
"This YANG module augments the ietf-mud model to provide for
reporting of SBOMs.
Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
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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 2020-03-06 {
description
"Initial proposed standard.";
reference
"RFC XXXX: Extension for MUD Reporting";
}
grouping mud-sbom-extension {
description
"SBOM extension grouping";
list sboms {
key "version-info";
leaf version-info {
type string;
description
"A version string that is applicable for this SBOM list entry.
The format of this string is left to the device manufacturer.
How the network administrator determines the version of
software running on the device is beyond the scope of this
memo.";
}
choice sbom-type {
case url {
leaf sbom-url {
type inet:uri;
description
"A statically located URI.";
}
}
case local-uri {
leaf-list sbom-local {
type enumeration {
enum coap {
description
"Use COAP schema to retrieve SBOM";
}
enum coaps {
description
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"Use COAPS schema to retrieve SBOM";
}
enum http {
description
"Use HTTP schema to retrieve SBOM";
}
enum https {
description
"Use HTTPS schema to retrieve SBOM";
}
}
description
"The choice of sbom-local means that the SBOM resides at
a location indicated by an indicted scheme for the
device in question, at well known location
'/.well-known/sbom'. For example, if the MUD file
indicates that coaps is to be used and the host is
located at address 10.1.2.3, the SBOM could be retrieved
at 'coaps://10.1.2.3/.well-known/sbom'. N.B., coap and
http schemes are NOT RECOMMENDED.";
}
}
case contact-info {
leaf contact-uri {
type inet:uri;
description
"This MUST be either a tel, http, https, or
mailto uri schema that customers can use to
contact someone for SBOM information.";
}
}
description
"choices for SBOM retrieval.";
}
description
"list of methods to get an SBOM.";
}
}
augment "/mud:mud" {
description
"Add extension for SBOMs.";
uses mud-sbom-extension;
}
}
<CODE ENDS>
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4. Examples
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.
4.1. Without ACLS
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://iot-device.example.com/dnsname",
"last-update": "2019-01-15T10:22:47+00:00",
"cache-validity": 48,
"is-supported": true,
"systeminfo": "device that wants to talk to a cloud service",
"mfg-name": "Example, Inc.",
"documentation": "https://frobinator.example.com/doc/frob2000",
"model-name": "Frobinator 2000",
"extensions" : [
"sbom"
],
"sboms" : [
{
"version-info" : "FrobOS Release 1.1",
"sbom-url" : "https://frobinator.example.com/sboms/f20001.1",
}
]
}
}
4.2. Located on the Device
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{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://iot-device.example.com/dnsname",
"last-update": "2019-01-15T10:22:47+00:00",
"cache-validity": 48,
"is-supported": true,
"systeminfo": "device that wants to talk to a cloud service",
"mfg-name": "Example, Inc.",
"documentation": "https://frobinator.example.com/doc/frob2000",
"model-name": "Frobinator 2000",
"extensions" : [
"sbom"
],
"sboms" : [
{
"version-info" : "FrobOS Release 1.1",
"sbom-local" : "coaps:///.well-known/sbom",
}
]
}
}
4.3. SBOM Obtained from Contact Information
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://iot-device.example.com/dnsname",
"last-update": "2019-01-15T10:22:47+00:00",
"cache-validity": 48,
"is-supported": true,
"systeminfo": "device that wants to talk to a cloud service",
"mfg-name": "Example, Inc.",
"documentation": "https://frobinator.example.com/doc/frob2000",
"model-name": "Frobinator 2000",
"extensions" : [
"sbom"
],
"sboms" : [
{
"version-info" : "FrobOS Release 1.1",
"contact-uri" : "mailto:sbom-requst@example.com",
}
]
}
}
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4.4. With ACLS
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://iot-device.example.com/dnsname",
"last-update": "2019-01-15T10:22:47+00:00",
"cache-validity": 48,
"is-supported": true,
"systeminfo": "device that wants to talk to a cloud service",
"mfg-name": "Example, Inc.",
"documentation": "https://frobinator.example.com/doc/frob2000",
"model-name": "Frobinator 2000",
"extensions" : [
"sbom"
],
"sboms" : [
{
"version-info" : "FrobOS Release 1.1",
"sbom-url" : "https://frobinator.example.com/sboms/f20001.1",
}
],
"from-device-policy": {
"access-lists": {
"access-list": [
{
"name": "mud-96898-v4fr"
},
{
"name": "mud-96898-v6fr"
}
]
}
},
"to-device-policy": {
"access-lists": {
"access-list": [
{
"name": "mud-96898-v4to"
},
{
"name": "mud-96898-v6to"
}
]
}
}
},
"ietf-access-control-list:acls": {
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"acl": [
{
"name": "mud-96898-v4to",
"type": "ipv4-acl-type",
"aces": {
"ace": [
{
"name": "cl0-todev",
"matches": {
"ipv4": {
"ietf-acldns:src-dnsname": "cloud-service.example.com"
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-96898-v4fr",
"type": "ipv4-acl-type",
"aces": {
"ace": [
{
"name": "cl0-frdev",
"matches": {
"ipv4": {
"ietf-acldns:dst-dnsname": "cloud-service.example.com"
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-96898-v6to",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-todev",
"matches": {
"ipv6": {
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"ietf-acldns:src-dnsname": "cloud-service.example.com"
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-96898-v6fr",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-frdev",
"matches": {
"ipv6": {
"ietf-acldns:dst-dnsname": "cloud-service.example.com"
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
}
]
}
}
At this point, the management system can attempt to retrieve the
SBOM, and determine which format is in use through the content-type
header on the response to a GET request.
5. Security Considerations
SBOMs provide an inventory of software. If firmware is available to
an attacker, the attacker may well already be able to derive this
very same software inventory. Manufacturers MAY restrict access to
SBOM information using appropriate authorization semantics within
HTTP. In particular, if a system attempts to retrieve an SBOM via
HTTP, 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
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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.
6. IANA Considerations
6.1. MUD Extension
The IANA is requested to add "controller-candidate" to the MUD
extensions registry as follows:
Extension Name: sbom
Standard reference: This document
6.2. 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 19970-2 and SPDX.org
7. References
7.1. 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>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8520] Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
Description Specification", RFC 8520,
DOI 10.17487/RFC8520, March 2019,
<https://www.rfc-editor.org/info/rfc8520>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
7.2. Informative References
[CycloneDX12]
cylonedx.org, "CycloneDX XML Reference v1.2", May 2020.
[SPDX] The Linux Foundation, "SPDX Specification 2.1", 2016.
[SWID] ISO/IEC, "Information technology -- IT asset management --
Part 2: Software identification tag", ISO 19770-2:2015,
2015.
Appendix A. Changes from Earlier Versions
Draft -00:
o Initial revision
Authors' Addresses
Eliot Lear
Cisco Systems
Richtistrasse 7
Wallisellen CH-8304
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
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Scott Rose
NIST
100 Bureau Dr
Gaithersburg MD 20899
USA
Phone: +1 301-975-8439
Email: scott.rose@nist.gov
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