draft-ietf-opsawg-mud-acceptable-urls-00.txt		draft-ietf-opsawg-mud-acceptable-urls-01.txt
	OPSAWG Working Group M. Richardson		OPSAWG Working Group M. Richardson
	Internet-Draft Sandelman Software Works		Internet-Draft Sandelman Software Works
	Updates: 8520 (if approved) W. Pan		Updates: 8520 (if approved) W. Pan
	Intended status: Best Current Practice Huawei Technologies		Intended status: Best Current Practice Huawei Technologies
	Expires: 30 July 2021 E. Lear		Expires: 5 August 2021 E. Lear
	Cisco Systems		Cisco Systems
	26 January 2021		1 February 2021
	Authorized update to MUD URLs		Authorized update to MUD URLs
	draft-ietf-opsawg-mud-acceptable-urls-00		draft-ietf-opsawg-mud-acceptable-urls-01
	Abstract		Abstract
	This document provides a way for an RFC8520 Manufacturer Usage		This document provides a way for an RFC8520 Manufacturer Usage
	Description (MUD) definitions to declare what are acceptable		Description (MUD) definitions to declare what are acceptable
	replacement MUD URLs for a device.		replacement MUD URLs for a device.
	RFCEDITOR-please-remove: this document is being worked on at:		RFCEDITOR-please-remove: this document is being worked on at:
	https://github.com/mcr/iot-mud-acceptable-urls		https://github.com/mcr/iot-mud-acceptable-urls
	skipping to change at page 1, line 38 ¶		skipping to change at page 1, line 38 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on 30 July 2021.		This Internet-Draft will expire on 5 August 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2021 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	and restrictions with respect to this document. Code Components		and restrictions with respect to this document. Code Components
	extracted from this document must include Simplified BSD License text		extracted from this document must include Simplified BSD License text
	as described in Section 4.e of the Trust Legal Provisions and are		as described in Section 4.e of the Trust Legal Provisions and are
	provided without warranty as described in the Simplified BSD License.		provided without warranty as described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Updating MUD URLs vs Updating MUD files . . . . . . . . . . . 3		2. Updating MUD URLs vs Updating MUD files . . . . . . . . . . . 3
	2.1. Updating the MUD file in place . . . . . . . . . . . . . 3		2.1. Updating the MUD file in place . . . . . . . . . . . . . 3
	2.1.1. Adding capabilities . . . . . . . . . . . . . . . . . 3		2.1.1. Adding capabilities . . . . . . . . . . . . . . . . . 4
	2.1.2. Removing capabilities . . . . . . . . . . . . . . . . 4		2.1.2. Removing capabilities . . . . . . . . . . . . . . . . 4
	2.1.3. Significant changes to protocols . . . . . . . . . . 5		2.1.3. Significant changes to protocols . . . . . . . . . . 5
	2.2. Motivation for updating MUD URLs . . . . . . . . . . . . 5		2.2. Motivation for updating MUD URLs . . . . . . . . . . . . 5
	3. Threat model for MUD URLs . . . . . . . . . . . . . . . . . . 5		3. Threat model for MUD URLs . . . . . . . . . . . . . . . . . . 5
	3.1. Trust on First Use (TOFU): leveraging the manufacturer		3.1. Trust on First Use (TOFU): leveraging the manufacturer
	signature . . . . . . . . . . . . . . . . . . . . . . . . 5		signature . . . . . . . . . . . . . . . . . . . . . . . . 6
	3.2. Concerns about same-signer mechanism . . . . . . . . . . 6		3.2. Concerns about same-signer mechanism . . . . . . . . . . 6
	4. Outline of proposed mechanism . . . . . . . . . . . . . . . . 6		4. Outline of proposed mechanism . . . . . . . . . . . . . . . . 7
	5. Changes to RFC8520 . . . . . . . . . . . . . . . . . . . . . 6		5. Changes to RFC8520 . . . . . . . . . . . . . . . . . . . . . 7
	6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8		6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 8		7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	7.1. Updating files vs Updating MUD URLs . . . . . . . . . . . 9		7.1. Updating files vs Updating MUD URLs . . . . . . . . . . . 9
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
	8.1. Normative References . . . . . . . . . . . . . . . . . . 9		8.1. Normative References . . . . . . . . . . . . . . . . . . 10
	8.2. Informative References . . . . . . . . . . . . . . . . . 9		8.2. Informative References . . . . . . . . . . . . . . . . . 10
	Appendix A. Appendices . . . . . . . . . . . . . . . . . . . . . 10		Appendix A. Appendices . . . . . . . . . . . . . . . . . . . . . 11
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10		Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 11
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
	1. Introduction		1. Introduction
	[RFC8520] provides a standardized way to describe how a specific		[RFC8520] provides a standardized way to describe how a specific
	purpose device makes use of Internet resources and associated		purpose device makes use of Internet resources and associated
	suggested network behavior, which are describled in a MUD file hosted		suggested network behavior, which are describled in a MUD file hosted
	in its manufacture's server. By providing a MUD URL, the network		in its manufacture's server. By providing a MUD URL, the network
	manager can locate this MUD file. MUD URLs can come from a number of		manager can locate this MUD file. MUD URLs can come from a number of
	sources:		sources:
	* IDevID Extensions		* IDevID Extensions
	* DHCP option		* DHCP option
	* LLDP TLV		* LLDP TLV
	* [I-D.richardson-opsawg-securehomegateway-mud] proposes to scan		* [I-D.richardson-mud-qrcode] proposes to scan them from QRcodes.
	them from QRcodes.
	The IDevID mechanism provides a URL that is asserted		The IDevID mechanism provides a URL that is asserted
	cryptographically by a manufacturer. However, it is difficult for		cryptographically by a manufacturer. However, it is difficult for
	manufacturers to update the IDevID of a device which is already in a		manufacturers to update the IDevID of a device which is already in a
	box.		box.
	The DHCP and LLDP mechanisms are not signed, but are asserted by the		The DHCP and LLDP mechanisms are not signed, but are asserted by the
	device. A firmware update may update what MUD URL is emitted.		device. A firmware update may update what MUD URL is emitted.
	Sufficiently well targetted malware could also change the MUD URL.		Sufficiently well targetted malware could also change the MUD URL.
	The QRcode mechanism is usually done via paper/stickers, and is		The QRcode mechanism is usually done via paper/stickers, and is
	typically not under the control of the device itself at all.		typically not under the control of the device itself at all.
			However, being applied by a human and not easily changed, a MUD URL
			obtained in this fashion is likely trustworthy. (It may not, due to
			mixups in labelling represent the correct device, but this is a human
			coordination issue, and is out of scope for this document)
	While MUD files may include signatures, it is not mandatory to check		While MUD files may include signatures, [RFC8520] does not mandate
	them, and there is not a clear way to connect the entity which signed		checking them, and there is not a clear way to connect the entity
	the MUD file to the device itself. A malicious device does not need		which signed the MUD file to the device itself.
	to make up a MUD file if there is already an available, and already
	trusted MUD file which it can use to impersonate the device.
	One defense against this is to not trust MUD URLs which are different		This document limits itself to situations in which the MUD file is
	from the one that was placed in an IDevID. Or if the initial MUD URL		signed, and that the MUD controller has been configured to always
	was not taken from an IDevID, it could be trusted on first use. But,		check the signatures, rejecting files whose signatures do not match.
	if the MUD controller has locked down the URL, then updates to the
	URL are difficult to do.		[RFC8520] does not specify how MUD controllers establish their trust
			in the manufacturers' signing key: there are many possible solutions
			from manual configuration of trust anchors, some kind of automatic
			configuration during onboarding, but also including to Trust on First
			Use (TOFU). How this initial trust is established is not important
			for this document, it is sufficient that some satisfactory initial
			trust is established.
	2. Updating MUD URLs vs Updating MUD files		2. Updating MUD URLs vs Updating MUD files
	There are two ways in which a manufacturer can change what the is		There are two ways in which a manufacturer can change what the is
	processed by the MUD controller: they can change what is in the MUD		processed by the MUD controller: they can change what is in the MUD
	file (update-in-place), and or they change which file is processed by		file (update-in-place), and or they change which file is processed by
	the MUD controller by changing the URL (updated-url).		the MUD controller by changing the URL (updated-url).
	2.1. Updating the MUD file in place		2.1. Updating the MUD file in place
	skipping to change at page 4, line 45 ¶		skipping to change at page 5, line 11 ¶
	are to be turned off or removed in subsequent versions of the		are to be turned off or removed in subsequent versions of the
	firmware, the MUD file will be updated to disallow connections that		firmware, the MUD file will be updated to disallow connections that
	previously were allowed.		previously were allowed.
	In this case, the new MUD file will forbid some connection which the		In this case, the new MUD file will forbid some connection which the
	old firmware still expects to do. As explained in the previous		old firmware still expects to do. As explained in the previous
	section, upgrades may not always occur immediately upon release of		section, upgrades may not always occur immediately upon release of
	the new firmware.		the new firmware.
	In this case the old device will be performing unwanted connections,		In this case the old device will be performing unwanted connections,
	and the MUD controller when be alerting the device owner that the		and the MUD controller will then send alerts to the network owner
	device is mis-behaving. This causes a false positive situation (see		that the device is mis-behaving. This causes a false positive
	[boycrieswolf]), leading to real security issues being ignored. This		situation (see [boycrieswolf]), leading to real security issues being
	is a serious issue as documented also in [boywolfinfosec], and		ignored. This is a serious issue as documented also in
	[falsemalware].		[boywolfinfosec], and [falsemalware].
	2.1.3. Significant changes to protocols		2.1.3. Significant changes to protocols
	[I-D.reddy-opsawg-mud-tls] suggests MUD definitions to allow		[I-D.reddy-opsawg-mud-tls] suggests MUD definitions to allow
	examination of TLS protocol details. Such a profile may be very		examination of TLS protocol details. Such a profile may be very
	specific to the TLS library which is shipped in a device. Changes to		specific to the TLS library which is shipped in a device. Changes to
	the library (including bug fixes) may cause significant changes to		the library (including bug fixes) may cause significant changes to
	the profile, requiring changes to the profile described in the MUD		the profile, requiring changes to the profile described in the MUD
	file. Such changes are likely neither forward nor backward		file. Such changes are likely neither forward nor backward
	compatible with other versions, and in place updates to MUD files are		compatible with other versions, and in place updates to MUD files are
	skipping to change at page 6, line 22 ¶		skipping to change at page 6, line 35 ¶
	There is still a potential threat: a manufacturer which has many		There is still a potential threat: a manufacturer which has many
	products may have a MUD definition for another product that has the		products may have a MUD definition for another product that has the
	privileges that the malware desires.		privileges that the malware desires.
	The malware could simply change the expressed MUD URL to that of the		The malware could simply change the expressed MUD URL to that of the
	other product, and it will be accepted by the MUD controller as		other product, and it will be accepted by the MUD controller as
	valid.		valid.
	This works as long as manufacturers use a single key to sign all		This works as long as manufacturers use a single key to sign all
	products. Some manufacturers could sign each product with a		products. Some manufacturers could sign each product with a
	different key. Possibly, all the keys are collected into a single		different key. Going logically down this path, if all these product
	PKI, signed by a common certification authority. In this case, the		keys are collected into a single PKI, signed by a common
	question as to whether the MUD controller should pin the end-entity		certification authority.
	(EE) certificate, or the CA certificate. Pinning the EE certificate
	defends against malware that changes the product type, but keeps the		In this case, the question then becomes whether the MUD controller
	manufacturer from being able to cycle the validity of the End-Entity		should pin the end-entity (EE) certificate, or the CA certificate.
	Certificate for cryptographic hygiene reasons. Pinning the CA
	certificate allows the EE certificate to change, but may not defend		Pinning the EE certificate defends against malware that changes the
	against product type changes.		product type, but keeps the manufacturer from being able to cycle the
			validity of the End-Entity Certificate for cryptographic hygiene
			reasons.
			Pinning the CA certificate allows the EE certificate to change, but
			may not defend against product type changes.
	It is possible to invent policy mechanisms that would link the EE		It is possible to invent policy mechanisms that would link the EE
	certificate to a value that is in the MUD file. This could be a		certificate to a value that is in the MUD file. This could be a
	policy OID, or could involve some content in a subjectAltName.		policy OID, or could involve some content in a subjectAltName.
	Future work could go in this direction. This document proposes a		Future work could go in this direction. This document proposes a
	simpler solution.		simpler solution.
	4. Outline of proposed mechanism		4. Outline of proposed mechanism
	The document proposes to limit what MUD URLs are considered valid		The document proposes to limit what MUD URLs are considered valid
	skipping to change at page 7, line 40 ¶		skipping to change at page 8, line 16 ¶
	URI. The test is simplified to: remove everything to the right of		URI. The test is simplified to: remove everything to the right of
	the last (rightmost) "/" in the URL of "root" MUD file URL, and the		the last (rightmost) "/" in the URL of "root" MUD file URL, and the
	proposed new URL. The resulting two strings MUST be identical.		proposed new URL. The resulting two strings MUST be identical.
	For as a simple example, if the "root" mud-url is		For as a simple example, if the "root" mud-url is
	http://example.com/hello/there/file.json then any URL that starts		http://example.com/hello/there/file.json then any URL that starts
	with http://example.com/hello/there/ would be acceptable, such as		with http://example.com/hello/there/ would be acceptable, such as
	http://example.com/hello/there/revision2.json.		http://example.com/hello/there/revision2.json.
	Once the new MUD file is accepted, then it becomes the new "root" MUD		Once the new MUD file is accepted, then it becomes the new "root" MUD
	file, and any subsequent updates must be relative to the MUD-URL in		file, and any subsequent updates MUST be relative to the MUD-URL in
	the new file.		the new file.
	This process allows a manufacturer to rework their file structure, to		This process allows a manufacturer to rework their file structure, to
	change web server hostnames (such as when there is an acquisition or		change web server hostnames (such as when there is an acquisition or
	merger), etc. so long as they retain the old structure long enough		merger), etc. so long as they retain the old structure long enough
	for all devices to upgrade at least once.		for all devices to upgrade at least once.
	(XXX: how should the trust anchor for the signature be updated when		(XXX: how should the trust anchor for the signature be updated when
	there is Merger&Acquisition)		there is Merger&Acquisition)
	skipping to change at page 8, line 25 ¶		skipping to change at page 8, line 47 ¶
	7. Security Considerations		7. Security Considerations
	Prior to the standardization of the process in this document, if a		Prior to the standardization of the process in this document, if a
	device was infiltrated by malware, and said malware wished to make		device was infiltrated by malware, and said malware wished to make
	accesses beyond what the current MUD file allowed, the the malware		accesses beyond what the current MUD file allowed, the the malware
	would have to:		would have to:
	1. arrange for an equivalent MUD file to be visible somewhere on the		1. arrange for an equivalent MUD file to be visible somewhere on the
	Internet		Internet
	2. depend upon the MUD-manager either not checking signatures, or		2. depend upon the MUD controller either not checking signatures, or
	3. somehow get the manufacturer to sign the alternate MUD		3. somehow get the manufacturer to sign the alternate MUD
	4. announce this new URL via DHCP or LLDP, updating the MUD-manager		4. announce this new URL via DHCP or LLDP, updating the MUD
	with the new permissions.		controller with the new permissions.
	One way to accomplish (3) is to leverage the existence of MUD files		One way to accomplish (3) is to leverage the existence of MUD files
	created by the manufacturer for different classes of devices. Such		created by the manufacturer for different classes of devices. Such
	files would already be signed by the same manufacturer, eliminating		files would already be signed by the same manufacturer, eliminating
	the need to spoof a signature.		the need to spoof a signature.
	With the standardization of the process in this document, then the		With the standardization of the process in this document, then the
	attacker can no longer point to arbitrary MUD files in step 4, but		attacker can no longer point to arbitrary MUD files in step 4, but
	can only make use of MUD files that the manufacturer has already		can only make use of MUD files that the manufacturer has already
	provided for this device.		provided for this device.
	Manufacturers are advised to maintain an orderly layout of MUD files		Manufacturers are advised to maintain an orderly layout of MUD files
	in their web servers, with each unique producting having its own		in their web servers, with each unique producting having its own
	directory/pathname.		directory/pathname.
	The process described updates only MUD-managers and the processes		The process described updates only MUD controllers and the processes
	that manufacturers use to manage the location of their MUD files.		that manufacturers use to manage the location of their MUD files.
	A manufacturer which has not managed their MUD files in the the way		A manufacturer which has not managed their MUD files in the the way
	described here can deploy new directories of per-product MUD files,		described here can deploy new directories of per-product MUD files,
	and then can update the existing MUD files in place to point to the		and then can update the existing MUD files in place to point to the
	new URLs using the MUD-URL attribute.		new URLs using the MUD-URL attribute.
	There is therefore no significant flag day: MUD managers may		There is therefore no significant flag day: MUD managers may
	implement the new policy without significant concern about backwards		implement the new policy without significant concern about backwards
	compatibility.		compatibility.
	skipping to change at page 10, line 30 ¶		skipping to change at page 10, line 50 ¶
	9 March 2020, <http://www.ietf.org/internet-drafts/draft-		9 March 2020, <http://www.ietf.org/internet-drafts/draft-
	jimenez-t2trg-mud-coap-00.txt>.		jimenez-t2trg-mud-coap-00.txt>.
	[I-D.reddy-opsawg-mud-tls]		[I-D.reddy-opsawg-mud-tls]
	Reddy.K, T., Wing, D., and B. Anderson, "MUD (D)TLS		Reddy.K, T., Wing, D., and B. Anderson, "MUD (D)TLS
	profiles for IoT devices", Work in Progress, Internet-		profiles for IoT devices", Work in Progress, Internet-
	Draft, draft-reddy-opsawg-mud-tls-05, 31 August 2020,		Draft, draft-reddy-opsawg-mud-tls-05, 31 August 2020,
	<http://www.ietf.org/internet-drafts/draft-reddy-opsawg-		<http://www.ietf.org/internet-drafts/draft-reddy-opsawg-
	mud-tls-05.txt>.		mud-tls-05.txt>.
	[I-D.richardson-opsawg-securehomegateway-mud]		[I-D.richardson-mud-qrcode]
	Richardson, M., Latour, J., and H. Gharakheili, "On		Richardson, M., Latour, J., and H. Gharakheili, "On
	loading MUD URLs from QR codes", Work in Progress,		loading MUD URLs from QR codes", Work in Progress,
	Internet-Draft, draft-richardson-opsawg-securehomegateway-		Internet-Draft, draft-richardson-mud-qrcode-00, 17
	mud-05, 8 September 2020, <http://www.ietf.org/internet-		December 2020, <http://www.ietf.org/internet-drafts/draft-
	drafts/draft-richardson-opsawg-securehomegateway-mud-		richardson-mud-qrcode-00.txt>.
	05.txt>.
	Appendix A. Appendices		Appendix A. Appendices
			Contributors
			Tianqing Tang
			Email: tangtianqing@huawei.com
	Authors' Addresses		Authors' Addresses
	Michael Richardson		Michael Richardson
	Sandelman Software Works		Sandelman Software Works
	Email: mcr+ietf@sandelman.ca		Email: mcr+ietf@sandelman.ca
	Wei Pan		Wei Pan
	Huawei Technologies		Huawei Technologies
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