| Internet-Draft | Discovering SBOMs and Vuln. Info | February 2023 |
| Lear & Rose | Expires 31 August 2023 | [Page] |
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.¶
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/.¶
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This Internet-Draft will expire on 31 August 2023.¶
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.¶
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:¶
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:¶
To satisfy these two key use cases, objects may be found in one of three methods:¶
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.¶
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.¶
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.¶
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.¶
A well-known endpoint is defined:¶
As discussed previously, the precise format of a response is based on the Content-type provided.¶
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
¶
<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";
}
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
"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
"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";
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>¶
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.¶
This first MUD file demonstrates how to get SBOM and vulnerability information without ACLs.¶
{
"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"
}
}
¶
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"
}
}
¶
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": {
"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"
}
}
¶
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": {
"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, 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.¶
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.¶
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:¶
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.¶
The IANA is requested to add "transparency" to the MUD extensions registry as follows:¶
Extension Name: transparency Standard reference: This document¶
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.¶
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¶
Thanks to Russ Housley, Dick Brooks, Tom Petch, Nicolas Comstedt, who provided review comments.¶
Draft -04: * Address review comments¶
Draft -02:¶
Draft -01:¶
Draft -00:¶