Re: [OPSEC] Iotdir early review of draft-ietf-opsec-v6-21

"Eric Vyncke (evyncke)" <evyncke@cisco.com> Fri, 12 February 2021 15:31 UTC

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From: "Eric Vyncke (evyncke)" <evyncke@cisco.com>
To: Ted Lemon <mellon@fugue.com>
CC: Merike Kaeo <merike@doubleshotsecurity.com>, KK Chittimaneni <kk.chittimaneni@gmail.com>, Enno Rey <erey@ernw.de>, "opsec@ietf.org" <opsec@ietf.org>
Thread-Topic: [OPSEC] Iotdir early review of draft-ietf-opsec-v6-21
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Archived-At: <https://mailarchive.ietf.org/arch/msg/opsec/guA6e1s8xgBspbPDRsAZbg-PL8o>
Subject: Re: [OPSEC] Iotdir early review of draft-ietf-opsec-v6-21
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Ted,

As you guessed in your email : we, the authors, do not want to prevent multi-homing ;-)  E.g., we already have several ‘do not apply in all cases’ for several mitigation techniques include the RA-guard one for obvious reason.

Just to be clear, we have used your suggestion to modify the abstract and add an applicability statement in a -24 version (yet to be published). We would appreciate it if you reviewed the proposed change below.

--- start of abstract ---
   Knowledge and experience on how to operate IPv4 securely is
   available: whether it is the Internet or an enterprise internal
   network.  However, IPv6 presents some new security challenges.  RFC
   4942 describes the security issues in the protocol, but network
   managers also need a more practical, operations-minded document to
   enumerate advantages and/or disadvantages of certain choices.

   This document analyzes the operational security issues associated
   with several types of network and proposes technical and procedural
   mitigation techniques.  This document is only applicable to managed
   networks, such as enterprise building networks.  The recommendations
   in this document are not applicable to residential user cases, even
   in cases where a Service Provider may be managing the home gateway.

--- end of abstract ---

--- start of applicability statement (sub-section of introduction) ---
1.1.  Applicability Statement

   This document is applicable to managed networks, i.e., when the
   network is operated by the user organization itself.  Indeed, many of
   the recommended mitigation techniques must be configured with the
   detailed knowledge of the network (which are the default router,
   which are the switch trunk ports, etc.).  This covers Service
   Provider (SP), enterprise networks and some knowledgeable-home-user-
   managed residential network.  This applicability statement especially
   applies to Section 2.3 and Section 2.5.4.

   For example, an exception to the generic recommendations of this
   document is when a residential or enterprise network is multi-homed.


--- end of applicability statement (sub-section of introduction) ---

Regards

-éric

From: Ted Lemon <mellon@fugue.com>
Date: Tuesday, 9 February 2021 at 16:59
To: Eric Vyncke <evyncke@cisco.com>
Cc: Merike Kaeo <merike@doubleshotsecurity.com>om>, Kiran Kumar Chittimaneni <kk.chittimaneni@gmail.com>om>, Enno Rey <erey@ernw.de>de>, "opsec@ietf.org" <opsec@ietf.org>
Subject: Re: [OPSEC] Iotdir early review of draft-ietf-opsec-v6-21

Éric, to be clear, your latest changes do not successfully address my comments. For example, you talk about a managed ISP router, and say that it’s okay for such a router to do all kinds of blocking on the home network. It’s not—what does the ISP know of the home network? How is the ISP qualified to set security and reachability policy on the home network?

This will cause major operational problems. Any network on which this is deployed will break stub networks, such as are used by the HomePod Mini and Google’s Nest gateway to provide reachability to Thread networks.

The text that I think you added to address my concerns is this:


   The residential users case assumes a managed ISP CPE

   device.  Some very specific types of networks such as the Internet of

   Things (IoT) and unmanaged home networks are not discussed in this

   document.

This is not helping. The text should read this way:


   This document is only applicable to managed networks, such as enterprise

   building networks. The recommendations in this document are not applicable

   to residential user cases, even in cases where an ISP may be managing the

   home gateway.

If you really want this to apply to the ISP-managed home network router, it should only be in the case where the ISP is providing a value-added service—where the home user is actually paying for a person to manage their network, not just to have an ISP-owned router that maybe gets regular firmware updates and some centrally-managed malware site blocking. If you were to address this use case (which I think is really unnecessary), this document needs to talk about what an ISP would have to do to avoid creating interop problems for IoT networks in the home. This needs to be very explicit and needs to be mentioned in the sections where you talk about RA filtering and ND filtering.

Sorry to be a sticky wicket, but I am afraid I failed to fully communicate the seriousness of this problem back in 2019.

Also, I don’t mean to minimize the problem you are trying to address. I’m just saying that we don’t have the technology to address it right now, and trying to address it on an effectively unmanaged network with existing technology will create serious interoperability problems.

In addition to the IoT stub networks issue, following this document on a home network would also eliminate multi-homing, which I hope is not something that we are proposing to do.


On Feb 9, 2021, at 8:04 AM, Eric Vyncke (evyncke) <evyncke@cisco.com<mailto:evyncke@cisco.com>> wrote:

Ted,

Just to confirm that the revision -23 should have all your review items addressed except the 3 cited by Merike.

The section 2.3.2 has been revised extensively.

Thank you again for this review

-éric


-----Original Message-----
From: Merike Kaeo <merike@doubleshotsecurity.com<mailto:merike@doubleshotsecurity.com>>
Date: Thursday, 5 December 2019 at 20:13
To: Ted Lemon <mellon@fugue.com<mailto:mellon@fugue.com>>, Eric Vyncke <evyncke@cisco.com<mailto:evyncke@cisco.com>>, Kiran Kumar Chittimaneni <kk.chittimaneni@gmail.com<mailto:kk.chittimaneni@gmail.com>>, Enno Rey <erey@ernw.de<mailto:erey@ernw.de>>
Cc: <opsec@ietf.org<mailto:opsec@ietf.org>>
Subject: Re: [OPSEC] Iotdir early review of draft-ietf-opsec-v6-21

   Hello Ted.

   Very much appreciate the thorough review of the document.  All 4 authors agree with most of your comments which will be incorporated
   in the next revision (also includes the discussion between yourself, Gyan and Suresh re DHCPv6).  For the comment re  section 2.3.2 and
   RAs,  can you point us to the relevant specifications for the TBR (Threat Boarder Route) so that we can come up with a potential addition that discusses the (non-) applicability of RA for certain scenarios?

   For 3 comments the authors want to preserve the existing language for reasons stated below.

   2.1.1 on ULA: The very first draft had some specific language on ULA use and the topic of ULAs has been a major contention area to get to working group last call.  Some individuals felt for years that the discussion on ULA should be to state that they are not required and not recommended while others wanted to be more explicit on recommended language *if* ULAs are used.  The current language on ULAs reflects working group rough consensus after many iterations of language.  Te authors would recommend that the language not be changed at this point.

   2.1.7 re /64s.  The section references rfc8273 and the working group felt that re-iterating even in more detail that work, which provides the added context, was not necessary in the document itself

   Last comment on Isolation of Networks -  While we did not discuss varying network configurations, usually more explicit details are provided in the rfcs we reference.  rfc8273 referenced in Section 2.1.7 and rfc7721 referenced in section 2.1.8 are some examples.

   - merike



---

The document doesn't talk about its intended audience.  It appears to be the
case based on my reading of it that the intended audience is enterprise
operators and similar.  This should be stated clearly and explicitly.  Some of
the advice in this document would be actively harmful if deployed on an
unmanaged network (e.g. in a home).  That doesn't mean that the document is
bad—just that it needs to be scoped appropriately.   I would suggest adding a
brief statement of applicability in the abstract and a more detailed
explanation in the introduction.  It is important that this statement make
clear that the advice in this document must not be followed by implementers of
home routers and similar devices.   E.g., this advice would utterly break a
Thread (IPv6 over 802.15.4 mesh) Border Router.

It's also not clear that this document lives up to its abstract.   The abstract
says:

 This document analyzes the operational security issues in several
 places of a network (enterprises, service providers and residential
 users) and proposes technical and procedural mitigations techniques.

And yet if you look for example at section 2.1.1, there is no actual analysis
of the use of ULAs, nor is any advice on their use provided.

Section 2.1.4 doesn't mention using DHCP to provide hosts with obfuscated
address that, since known to the operator, can be added to filter lists as
appropriate, while still making probing mathematically challenging to an
outside attacker.

Section 2.1.6 incorrectly implies that DHCPv4 binds IP addresses to link-layer
addresses.  This is not true.  I don't know that it really matters, but since
it's not true, you should fix it.  DHCPv4 uses a "client identifier," which is
quite similar to a DUID.  If no client identifier is offered, then the
link-layer address is used, but this is not required, and the behavior
described for DUIDs in this document is also applicable to client identifiers.

2.1.7 seems to be continuing a thought that was started in 2.1.4.  It would be
worth stating that explicitly, and comparing and contrasting these approaches.

Although the abstract explicitly excludes applicability to IoT networks, the
advice in this document will necessarily be taken as applicable in situations
where IoT networks are leaf networks or even infrastructure that is present
alongside the networks that _are_ covered by this document.  This has some
specific impacts that aren't talked about here and should be.   For instance,
Manufacturer Usage Descriptions (MUD) are not mentioned, and should be.   MUD
is applicable to infrastructure devices and really any special-purpose device;
e.g., MUD would be highly appropriate for use in hospital environments where
many devices are connected to the network that absolutely must have their
accessibility controlled; MUD is a good candidate for doing this.   The
omission of this approach from section 2,1 is a major gap, since the issues
discussed in section 2.1 directly impact the feasibility of using MUD (since
MUD specifies firewall behavior for devices, and devices are necessarily
identified by source address).

The conclusion I'm drawing having gotten to the end of section 2.1, in addition
to what I've said above, is that some of the issues introduced in subsections
of section 2.1, like filterability of host addresses, really belong in the
initial section 2.1 introduction, so that the subsections of 2.1 can refer back
and give the reader a coherent picture, rather than requiring the reader to
synthesize this as they read through the subsections.

Section 2.3.2 talks about the threat of a MITM attack through the use of forged
RAs, but doesn't actually describe how prevalent such on-link attacks are (this
would be an on-link attack) nor does it talk about how such an on-link attack
would be more effective than an attack the attacker could do without this
capability.  Without a threat model, this is somewhat hypothetical.

Section 2.3.2 goes on to talk at length about how to make RA Guard work,
without talking about when it is useful, what attacks it prevents, and what
problems it causes when deployed incorrectly.  We have actually run into
serious problems working on the Thread Border Router specification because of
uncertainty about whether RA Guard may be present on a network to which the TBR
is attached.  If it is, then the easiest way for the TBR to advertise
reachability is gone, and we have to resort to bypasses such as ND Proxy,
reverse NAT64, NAT66, or tunnels, just in order to ensure reachability of the
leaf network.

I think it's actively harmful to recommend the use of RA guard without talking
about the problems it causes and how to mitigate them.  This section should
explicitly say that RA guard should never be enabled by default: it should be
the case that the operator enables it explicitly, and that in cases where there
is no operator with the authority to set routing policy for a link, RA guard
should not be used on that link.

SAVI is another extremely useful technology that can't really be deployed
automatically without creating similar problems.  To be clear, my goal here is
not to say that the document shouldn't recommend RA guard or SAVI, but rather
that it should be very clear about when to deploy it and when not to.

In section 2.3.5, what is a "generic operating system?"   I don't know what
this term means.   Can you use a term with a clearer meaning?

One thing I didn't see discussed in section 2 that I think belongs there is the
concept of isolation of networks.  Networks that provide connectivity to
general-purpose devices like phones and comouters may need to provide
flexibility of addressing for privacy reasons.  Infrastructure devices,
particularly those for which MUD is applicable, may need to be on networks
where filtering is present and addressing is tightly controlled.  There's no
discussion fo this kind of separation in the document, and I think it's a
serious gap.


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