-
Notifications
You must be signed in to change notification settings - Fork 2
/
opsawg-mud-acceptable-urls.txt
784 lines (496 loc) · 29.1 KB
/
opsawg-mud-acceptable-urls.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
OPSAWG Working Group M. Richardson
Internet-Draft Sandelman Software Works
Updates: 8520 (if approved) W. Pan
Intended status: Best Current Practice Huawei Technologies
Expires: 9 April 2022 E. Lear
Cisco Systems
6 October 2021
Authorized update to MUD URLs
draft-ietf-opsawg-mud-acceptable-urls-04
Abstract
This document provides a way for an RFC8520 Manufacturer Usage
Description (MUD) definitions to declare what are acceptable
replacement MUD URLs for a device.
RFCEDITOR-please-remove: this document is being worked on at:
https://github.com/mcr/iot-mud-acceptable-urls
Status of This Memo
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/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 9 April 2022.
Copyright Notice
Copyright (c) 2021 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
Richardson, et al. Expires 9 April 2022 [Page 1]
Internet-Draft mud-acceptable-urls October 2021
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Updating the MUD files in place . . . . . . . . . . . . . . . 3
2.1. Adding capabilities . . . . . . . . . . . . . . . . . . . 3
2.2. Removing capabilities . . . . . . . . . . . . . . . . . . 4
2.3. Significant changes to protocols . . . . . . . . . . . . 5
2.4. Motivation for updating MUD URLs . . . . . . . . . . . . 5
3. Updating the MUD URLs . . . . . . . . . . . . . . . . . . . . 5
3.1. Leveraging the manufacturer signature . . . . . . . . . . 6
3.2. Concerns about same-signer mechanism . . . . . . . . . . 6
4. Proposed mechanism . . . . . . . . . . . . . . . . . . . . . 7
4.1. Merger, Acquisitions and Key Changes . . . . . . . . . . 8
4.1.1. Changing file structure . . . . . . . . . . . . . . . 9
4.1.2. Changing hosting URLs . . . . . . . . . . . . . . . . 9
4.1.3. Changing Signing Authority . . . . . . . . . . . . . 9
5. Polling for changes in MUD files . . . . . . . . . . . . . . 10
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7.1. Updating files vs Updating MUD URLs . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Appendices . . . . . . . . . . . . . . . . . . . . . 13
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
[RFC8520] provides a standardized way to describe how a specific
purpose device makes use of Internet resources and associated
suggested network behavior. The behaviors are described in a MUD
file hosted in its manufacturer's server. The device provides a MUD
URL to the network manager, which can locate this MUD file and
determine the required network authorization of the device.
In some cases, e.g., the firmware update, the network behaviors of
the device may change, and the description in the original MUD file
will no longer apply. To solve this problem, there are two common
ways which the manufacturer can use.
Richardson, et al. Expires 9 April 2022 [Page 2]
Internet-Draft mud-acceptable-urls October 2021
One is to change what is in the MUD file, i.e., update the MUD file
in place, whenever the behavior of the firmware changes. Section 2
discusses three scenarios for updating the MUD file and the
corresponding potential issues.
The other is to change which MUD file is processed by changing the
MUD URL. Section 3 describes the common sources of MUD URLs and the
problems and threats faced by each type of source when updating the
MUD URL. This document proposes an enhanced mechanism of how to
securely update the MUD URL in Section 4.
There are also some assumptions and prerequisites in this document.
While MUD files may include signatures, [RFC8520] does not mandate
checking them, and there is not a clear way to connect the entity
which signed the MUD file to the device itself. This document limits
itself to situations in which the MUD file is signed, and that the
MUD controller has been configured to always check the signatures,
rejecting files whose signatures do not match.
[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 the MUD files in place
Three scenarios for updating the MUD file and the corresponding
potential issues are discussed below.
2.1. Adding capabilities
For situations where new capabilities are added to the firmware, the
MUD file will detail the new access that the new firmware requires.
This may involve new incoming or outgoing connections that should be
authorized. Devices that have been upgraded to the new firmware will
make use of the new features. Devices that have not been upgraded to
the new firmware may have new connections that are authorized, but
which the device does not use (outgoing connections), or which the
device is not prepared to respond to (new incoming connections).
It is possible that older versions of the firmware have
vulnerabilities that were not easily exploitable due to the MUD file
preventing particular kinds of access. For example, an older
firmware could have no credentials required (or default credentials)
Richardson, et al. Expires 9 April 2022 [Page 3]
Internet-Draft mud-acceptable-urls October 2021
access via telnet on port 23 or HTTP on port 80. The MUD file
protected the device such that it could either not be accessed at
all, or access was restricted to connections from a controller only.
Useful and needed upgrades to the firmware could add credentials to
that service, allowing it to be opened up for more general access.
The new MUD file would provide for such access, but when combined
with the weak security of the old firmware, it results in a
compromised device.
While there is an argument that old firmware was insecure and should
be replaced, it is often the case that the upgrade process involves
downtime, or can introduce risks due to needed evaluations not having
been completed yet. As an example: moving vehicles (cars, airplanes,
etc.) should not perform upgrades while in motion! It is probably
undesirable to perform any upgrade to an airplane outside of its
service facility. A vehicle owner may desire only to perform
software upgrades when they are at their residence. Should there be
a problem, they could make alternate arrangements for transportation.
This is constrasted with the situation when the vehicle is parked at,
for instance, a remote cabin. The situation for upgrades of medical
devices has even more considerations involving regulatory compliance.
2.2. Removing capabilities
For situations where existing capabilities prove to be a problem and
are to be turned off or removed in subsequent versions of the
firmware, the MUD file will be updated to disallow connections that
previously were allowed.
In this case, the new MUD file will forbid some connections, which
the old firmware still expects to do. As explained in the previous
section, upgrades may not always occur immediately upon releasing the
new firmware.
In this case, the old device will be performing unwanted connections,
and the MUD controller will be alerting the network owner that the
device is misbehaving rather than not upgraded. This causes a false-
positive situation (see [boycrieswolf]), leading to real security
issues being ignored. This is a serious issue as documented also in
[boywolfinfosec], and [falsemalware].
Richardson, et al. Expires 9 April 2022 [Page 4]
Internet-Draft mud-acceptable-urls October 2021
2.3. Significant changes to protocols
[I-D.ietf-opsawg-mud-tls] suggests MUD definitions to allow
examination of TLS protocol details. Such a profile may be very
specific to the TLS library which is shipped in a device. Changes to
the library (including bug fixes) may cause significant changes to
the profile, requiring changes to the profile described in the MUD
file. Such changes are likely neither forward nor backward
compatible with other versions, and in place updates to MUD files are
therefore not advised.
2.4. Motivation for updating MUD URLs
While many small tweaks to a MUD file can be done in place, the
situation described above, particularly when it comes to removing
capabilities will suggest that changes to the MUD URL are in order.
A strategy for doing this securely is needed, and the rest of this
document provides a mechanism to do this securely.
3. Updating the MUD URLs
MUD URLs can come from a number of sources:
* IDevID Extensions
* DHCP option
* LLDP TLV
* [I-D.richardson-mud-qrcode] proposes to scan them from QRcodes.
The IDevID mechanism provides a URL that is asserted
cryptographically by a manufacturer. However, it is difficult for
manufacturers to update the IDevID of a device which is already in a
box.
The DHCP and LLDP mechanisms are not signed, but are asserted by the
device. A firmware update may update what MUD URL is emitted.
Sufficiently well targeted malware would also be able to change the
MUD URL that is emitted.
The QRcode mechanism is usually done via paper/stickers, and is
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 labeling represent the correct device, but this is a human
coordination issue, and is out of scope for this document.)
Richardson, et al. Expires 9 April 2022 [Page 5]
Internet-Draft mud-acceptable-urls October 2021
The manufacturer can use all the four mechanisms above when
manufacturing the device. But when considering updating the
firmware, it seems like only the DHCP and LLDP mechanisms are
sufficiently easy to send the new MUD URL. Because of that
sensitivity, they may also be easily changed by malware!
There are mitigating mechanisms which may be enough to deal with this
problem when MUD files are signed by the manufacturer.
While [RFC8520] has established a mechanism for signing of MUD files,
the document does not define a way for a MUD controller to determine
who should sign the MUD file for a particular device.
[RFC8520] leaves this for a local policy. There are a number of
processes that could be used, but they require coordination of many
players. It is expected that each industrial vertical will work out
supply chain arrangements or other heuristics.
3.1. Leveraging the manufacturer signature
When the first time a signature of the MUD file related to a
particular device-type is verified by the MUD controller, the
identity of the signing authority is recorded. That it, the signing
authorith is pinned. This policy means that subsequent MUD files
must be signed by the same entity in order to be accepted.
The trust and acceptance of the first signer may come from many
sources, for example, it could be manual configured to trust which
signer, or using the IDevID mechanism for the first MUD URL and the
signer of the corresponding MUD file is more trustworthy, or the MUD
controller can use a Trust on First Use (TOFU) mechanism and trusts
the first signer by default.
Based upon this process, an update to the MUD URL would be valid if
the new MUD file was signed by the same entity that signed the
previous entry. This mechanism permits a replacement URL to be any
URL that the same manufacturer can provide.
3.2. Concerns about same-signer mechanism
There is still a potential threat: a manufacturer which has many
products may have a MUD definition for another product that has the
privileges that the malware desires.
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
valid.
Richardson, et al. Expires 9 April 2022 [Page 6]
Internet-Draft mud-acceptable-urls October 2021
This works as long as manufacturers use a single key to sign all
products. Some manufacturers could sign each product with a
different key. Going logically down this path, if all these product
keys are collected into a single PKI, signed by a common
certification authority.
In this case, the question then becomes whether the MUD controller
should pin the End-Entity (EE) certificate, or the CA certificate.
Pinning the End-Entity (EE) certificate defends against malware that
changes the product type, but prevents 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
certificate to a value that is in the MUD file. This could be a
policy OID, or could involve some content in a subjectAltName.
Future work could go in this direction. This document proposes a
simpler solution.
4. Proposed mechanism
The document proposes to limit what MUD URLs are considered valid
from the device, limiting new MUD URLs to be variations of the
initial (presumed to be secure) URL.
The first MUD file which is defined for a device can come from an
IDevID (which is considered more secure), or via Trust on First Use
with DHCP or LLDP or other mechanisms. This first, initially
trusted, MUD file will be called the "root" MUD file.
A MUD file contains a self-referential MUD-URL attribute that points
to the MUD file itself located on the vendor's website. While the
IDevID, DHCP and LLDP mechanisms only transmit a URL, there are some
newer, not yet standardized proposals that would fetch an entire MUD
file from the device, such as [I-D.jimenez-t2trg-mud-coap].
The MUD-URL MUST always be an Absolute URI: see [RFC3986] section
4.3.
The URL found in the MUD-URL attribute is to be called the canonical
MUD URL for the device.
Richardson, et al. Expires 9 April 2022 [Page 7]
Internet-Draft mud-acceptable-urls October 2021
The MUD-SIGNATURE attribute in the MUD file SHOULD be a relative URI
(see [RFC3986] section 4.2) with the (hierarchical) base URI for this
reference being the MUD-URL attribute.
When pinning the signature, the MUD controller SHOULD pin the lowest
Certification Authority (CA) that was used in the validation of the
CMS structure, along with the chain of Subject Names leading to the
signature. The MUD controller may need additional trust anchors
(including previously pinned ones) in order to verify that CA
certificate.
Subsequent MUD files are considered valid if:
* they have the same initial Base-URI as the MUD-URL, but may have a
different final part
* they are signed by an equivalent End Entity (same trusted CA and
same Subject Name) as the "root" MUD file.
Section 5.2 of [RFC3986] details many cases for calculating the Base-
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
proposed new URL. The resulting two strings MUST be identical.
For a simple example, if the "root" MUD-URL is
http://example.com/hello/there/file.json then any URL that starts
with http://example.com/hello/there/ would be acceptable, such as
http://example.com/hello/there/revision2.json.
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
the new file.
4.1. Merger, Acquisitions and Key Changes
The above process allows for a manufacturer to rework its file
structure. They can change web server host names, so long as they
retain the old structure long enough for all devices to upgrade at
least once.
The process also allows a manufacturer to change the EE certificate
and Certification Authority used for signing.
Richardson, et al. Expires 9 April 2022 [Page 8]
Internet-Draft mud-acceptable-urls October 2021
4.1.1. Changing file structure
A manufacturer has been hosting a MUD file at
https://example.com/household/products/mudfiles/toaster.json and
wishes to move it to https://example.com/mudfiles/toasters/model1945/
mud.json
The manufacturer simply changes the MUD-URL contained with the files
at the old location to have a value of
https://example.com/mudfiles/toasters/model1945/mud.json. The
manufacturer must continue to serve the files from the old location
for some time, or to return an HTTP 301 (Moved Permanently)
redirecting to the new location.
4.1.2. Changing hosting URLs
A manufacturer has been hosting a MUD file at
https://example.com/household/products/mudfiles/toaster.json and
wishes to move it to
https://mud.example/example.com/toasters/model1945/mud.json
The manufacturer simply changes the MUD-URL contained with the files
at the old location to have a value of
https://example.com/mudfiles/toasters/model1945/mud.json. The
manufacturer has to continue to host at the old location until such
time as it is sure that all MUD controllers have loaded the new data,
and that all devices in the field have upgraded their URL. A 301
Redirect that changed the hostname SHOULD NOT be accepted by MUD
controllers.
4.1.3. Changing Signing Authority
A manufacturer has been signing MUD files using an EE Certificate
with subjectAltName foo.example, issued by an internal Certification
Authority BAZ.
The manufacturer wishes to begin signing with an EE Certificate with
subjectAltname foo.example, but now signed by a public CA (call it:
Fluffy).
The manufacturer first creates a new MUD file with a new detached
signature file. Within this signature file, the manufacturer places
a certificate chain: Internal-CA BAZ->Fluffy, and then the Fluffy
Certificate, and then the foo.example certificate issued from Fluffy.
This supports changing certification authorities, but it does not
support changing the Subject Name of the signing entity.
Richardson, et al. Expires 9 April 2022 [Page 9]
Internet-Draft mud-acceptable-urls October 2021
5. Polling for changes in MUD files
The MUD file update mechanisms described in Section 2 requires that
the MUD controller poll for updates. The MUD controller will receive
no signal about a change from the device because the URL will not
have changed.
The manufacturer SHOULD serve mud files from a source for which ETag
Section 2.3 of [RFC7232] may be generated. Static files on disk
satisfy this requirement. MUD files generated from a database
process might not. The use of ETag allows a MUD controller to more
efficiently poll for changes in the file.
A manufacturer should also serve MUD files with an HTTP Max-Age
header as per Section 5.2.2.8 of [RFC7234].
The MUD controller should take the Max-Age as an indication of when
to next poll for updates to the MUD file. Values of less than 1
hour, or more than 1 month should be considered out of range, and
clamped into the range (1 hour, 1 month).
MUD controllers SHOULD add some random jitter to the timing of their
requests. MUD controllers MAY use a single HTTP(S)/1.1 connection to
retrieve all resources at the same destination.
6. Privacy Considerations
The MUD URL contains sensitive model and even firmware revision
numbers. Thus the MUD URL identifies the make, model and revision of
a device.
[RFC8520] already identifies this privacy concern, and suggests use
of TLS so that the HTTP requests that retrieve the MUD file do not
divulge that level of detail.
The requirement for the MUD controller to poll for changes results in
multiple interactions between the MUD controller and the
manufacturer. Even if HTTPS used, an observer of the traffic to that
manufacturer will be revealing, and [RFC8520] goes on to suggest use
of a proxy as well.
7. Security Considerations
Prior to the standardization of the process in this document, if a
device was infiltrated by malware, and said malware wished to make
accesses beyond what the current MUD file allowed, the the malware
would have to:
Richardson, et al. Expires 9 April 2022 [Page 10]
Internet-Draft mud-acceptable-urls October 2021
1. arrange for an equivalent MUD file to be visible somewhere on the
Internet
2. depend upon the MUD controller either not checking signatures, or
3. somehow get the manufacturer to sign the alternate MUD
4. announce this new URL via DHCP or LLDP, updating the MUD
controller with the new permissions.
One way to accomplish (3) is to leverage the existence of MUD files
created by the manufacturer for different classes of devices. Such
files would already be signed by the same manufacturer, eliminating
the need to spoof a signature.
With the standardization of the process in this document, then the
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
provided for this device.
Manufacturers are advised to maintain an orderly layout of MUD files
in their web servers, with each unique product having its own
directory/pathname.
The process described updates only MUD controllers and the processes
that manufacturers use to manage the location of their MUD files.
A manufacturer which has not managed their MUD files in the the way
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
new URLs using the MUD-URL attribute.
There is therefore no significant flag day: MUD controllers may
implement the new policy without significant concern about backwards
compatibility.
7.1. Updating files vs Updating MUD URLs
Device developers need to consider whether to make a change by
updating a MUD file, or updating the MUD URL.
MUD URLs can only be updated by shipping a new firmware. It is
reasonable to update the MUD URL whenever a new firmware release
causes new connectivity to be required. The updated mechanism
defined in this document makes this a secure operation, and there is
no practical limitation on the number of files that a web server can
hold.
Richardson, et al. Expires 9 April 2022 [Page 11]
Internet-Draft mud-acceptable-urls October 2021
In place updates to a MUD file should be restricted to cases where it
turns out that the description was inaccurate: a missing connection,
an inadvertent one authorized, or just incorrect information.
Developers should be aware that many enterprise web sites use
outsourced content distribution networks, and MUD controllers are
likely to cache files for some time. Changes to MUD files will take
some time to propagate through the various caches. An updated MUD
URL will however, not experience any cache issues, but can not be
deployed with a firmware update.
8. References
8.1. Normative References
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[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>.
8.2. Informative References
[boycrieswolf]
"The Boy Who Cried Wolf", 18 January 2020,
<https://fablesofaesop.com/the-boy-who-cried-wolf.html>.
[boywolfinfosec]
"Security Alerts - A Case of the Boy Who Cried Wolf?", 18
January 2020, <https://www.infosecurity-
magazine.com/opinions/security-alerts-boy-cried-wolf/>.
[falsemalware]
"False malware alerts cost organizations $1.27M annually,
report says", 18 January 2020,
<https://www.scmagazine.com/home/security-news/false-
malware-alerts-cost-organizations-1-27m-annually-report-
says/ and http://go.cyphort.com/Ponemon-Report-Page.html>.
Richardson, et al. Expires 9 April 2022 [Page 12]
Internet-Draft mud-acceptable-urls October 2021
[I-D.ietf-opsawg-mud-tls]
Reddy, T., Wing, D., and B. Anderson, "Manufacturer Usage
Description (MUD) (D)TLS Profiles for IoT Devices", Work
in Progress, Internet-Draft, draft-ietf-opsawg-mud-tls-05,
27 July 2021, <https://www.ietf.org/archive/id/draft-ietf-
opsawg-mud-tls-05.txt>.
[I-D.jimenez-t2trg-mud-coap]
Jimenez, J., "Using MUD on CoAP environments", Work in
Progress, Internet-Draft, draft-jimenez-t2trg-mud-coap-00,
9 March 2020, <https://www.ietf.org/archive/id/draft-
jimenez-t2trg-mud-coap-00.txt>.
[I-D.richardson-mud-qrcode]
Richardson, M., Latour, J., and H. H. Gharakheili, "On
loading MUD URLs from QR codes", Work in Progress,
Internet-Draft, draft-richardson-mud-qrcode-01, 15 May
2021, <https://www.ietf.org/archive/id/draft-richardson-
mud-qrcode-01.txt>.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
DOI 10.17487/RFC7232, June 2014,
<https://www.rfc-editor.org/info/rfc7232>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>.
Appendix A. Appendices
Contributors
Jie Yang
Email: jay.yang@huawei.com
Tianqing Tang
Email: tangtianqing@huawei.com
Authors' Addresses
Richardson, et al. Expires 9 April 2022 [Page 13]
Internet-Draft mud-acceptable-urls October 2021
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
Wei Pan
Huawei Technologies
Email: william.panwei@huawei.com
Eliot Lear
Cisco Systems
Email: lear@cisco.com
Richardson, et al. Expires 9 April 2022 [Page 14]