Original text:
8.3. Services that run over UDP unprotected are vulnerable to unknowingly <del> become part of a DDoS attack as UDP does not require return routability check.  Therefore, an attacker can easily spoof the source IP of the target entity and send requests to such a service which would then respond to the target entity.  This can be used for large-scale DDoS attacks on the target.  Especially, if the service returns a response that is order of magnitudes larger than the request, the situation becomes even worse as now the attack can be amplified.  DNS servers have been widely used for DDoS amplification attacks.  There is also a danger that NTP Servers could become implicated in denial-of-service (DoS) attacks since they run on unprotected UDP, there is no return routability check, and they can have a large amplification factor.  The responses from the NTP server were found to be 19 times larger than the request.  An RD which responds to wild-card lookups is potentially vulnerable if run with CoAP over UDP.  Since there is no return routability check and the responses can be significantly larger than requests, RDs can unknowingly become part of a DDoS amplification attack. </del>  RFC7252 describes this at length in its Section 11.3, including some mitigation by using small block sizes in responses.  The upcoming I- a row is way below that because only the colliding node(s) will retry).  changes from -24 to -25 Large rework of section 7 (Security policies)

Reviewer comments:
This addresses a note from the SecDir review[1] and follows an earlier suggestion[2]. [1]: URL [2]: URL
Before the 2020-08-13 telechat, some reviews have come in: : Not Ready Minor: Clarification on "subject" -- my intention was to include anything "subject", but I don't really know what else to put in there. Minor: Why is the first attempt special? -- Can clarify, PR to come. [edit: ] Nits addressed in URL More nits (IDnits) do not require editing, but some explanation -- where would that go? Shepherd writeup? (that would be → NAME : Ready Notes that the DDOS mitigation section is a bit history heavy. I had similar comment in URL; should we use that comment to shorten here? [edit: If so, would want an ACK.] "It is my impression, that Security Considerations were mostly written having in mind that (D)TLS is always used, however it is only "SHOULD" in this draft (or even "MAY" if we look at RFC6690 which Security Considerations this draft refers to). I think that adding a few words describing which consequences for security not using (D)TLS would have and in which cases it is allowed will make the Security Considerations more consistent. " -- [edit: covered in ] I'll issue PRs for what I think we can do something about quickly, but won't merge them or create a -26 without an ACK on them (given we're late in the whole publication stage and my impression is that ill-coordinated uploads do more harm than good) and will follow up on this comment when they're ready for review.
With the additional reviews that have come in today, I see no point in addressing some of what has come in in a pre-telechat update (as we can't resolve all the discuss points) -- taking the urgency off this. I'll still file PRs for changes resulting from the reviewer comments. Procedurally (so this goes to NAME or NAME Is the general expectation with IESG comments that the text be further improved to answer all the points (especially when they are comments), or can a plain "we did it that way because" suffice? In the latter case, would it make sense to collect point-to-point responses here so they get author or WG review before "we" answer them?
With URL and its follow-ups sent out, this is closed; any further comments will be opened as new issues.
From Adam's Secdir review, this is something we should address. The hard part is the "how", as echo-request-tag is about to update 7252 with a concrete suggestion (which would apply to RD implicitly), but saying that here would create a normative (forward? they're not far apart) reference between otherwise unrelated documents. It might be worth adding a note that a simple registration doesn't need special consideration in that respect, as the GET .well-known/core is not significantly larger than the POST /rd -- at least from a DDOS point of view. (By the way, that whole paragraph is quite a mouthful, reads a bit like a history lesson -- I wonder why that didn't occur to me earlier, but changing such things now is probably hard; let's leave it to a summarizing "but in the end that's what you do against it") Hello Reviewers, CoRE and IESG members, thanks for your input to the Resource Directory document, and your patience while it was being processed. Before the individual point to point responses can go out, this mail is to address the general status, and answer a few points that were brought up by different reviewers (it will be referred back to in the point to point responses). In summary, the points raised in the reviews led to the changes of the recently uploaded [-26], and where no changes were made, the reasoning behind the choices in the document is outlined below or in the following mails. (Either way, short of aggregated nits paragraphs, all points are responded to in the following mails). A few larger issues evolved from the review comments being discussed in the interim meetings, so please expect a -27 at a later point (after IETF109) with the changes mentioned below. Kind regards Christian [-26]: URL Preface References into the issue tracker are primarily intended for bookkeeping and to give you access to the altered text if you're curious -- but for general review purposes, the responses are self-contained. Anticipated changes We have opted to submit a new version that should clear out all the other comments, so that the remaining work can be focused and swift: Replay and Freshness (OPEN-REPLAY-FRESHNESS) The comment on DTLS replay made us reevaluate the security properties of operations on the registration resource. While these are successively harder going from DTLS without replay protection to DTLS with replay protection and hardest with OSCORE, the text as it is is still vulnerable to an attacker stopping a reoccurring registration, or undoing alterations in registration attributes. Mitigation from a concurrent document (the Echo mechanism of I-D.ietf-core-echo-request-tag in event freshness mode) is planned, but the text is not complete yet. Necessity of the value in all responses The requirements around Limited Link Format and the necessity to express all looked up links in fully resolved form have stemmed from different ways RFC6690 has been read, both in the IETF community and by implementers. A comment from Esko Dijk has shown a clear error in one of the readings. That reading is single-handedly responsible for most of the overhead in the wire format (savings can go up to 50%), which is of high importance to the CoRE field. Due to that, it is the WG's and authors' intention to remove the reading from the set of interpretations that led to the rules set forth. The change will not render any existing RD server implementation incompatible (older RDs would merely be needlessly verbose), and the known implementations of Link-Format parsers can easily be updated. The updates to the document could not be completed in time with the rest of the changes, because a) it requires revisiting the known implementations for confirmation and b) will affect almost every example that contains lookup results. Server authorization (OPEN-SERVER) The two areas of "how is the RD discovery secured" and "what do applications based on the RD need to consider" jointly opened up new questions about server authorization and the linkage between a client's intention and the server's promises that may easily not conclusde in timeframe reasonable for RD. While steps have been taken to address the issue both on the RD discovery and the applications side (URL), the ongoing discussions in the working group may turn up with a less cumbersome phrasing for these parts. There's a few small open issues Esko brought up on the issue tracker that could not be addressed in time; most of them are about enhancing the examples, which best happens after the anchor cleanup anyway. Repeated topics A few common topics came up in multiple reviews, and are addressed in the following section; the individual responses can be found in follow-up mails, and refer to the common topics as necesary. GENERIC-FFxxDB "Where do the ff35:30:2001:... addresses come from?" response: There's a coverage gap between RFC3849 (defining example unicast addresses) and RFC3306 (defining unicast-prefix-based multicast addresses). For lack of an agreed-on example multicast address, the used ones were created by applying the unicast-prefix derivation process to the example address. The results (ff35:30:2001:db8::1) should be intuitively recognizable both as a multicast address and as an example address. The generated address did, however, fail to follow the guidance of RFC 3307 and set the first bit of the Group ID. Consequently, the addresses were changed from ff35:30:2001:db8::x to ff35:30:2001:db8::8000:x, which should finally be a legal choice of a group address for anyone operating the 2001:db8:: site. (The changes can be viewed at URL). GENERIC-6MAN "Whas this discussed with 6MAN?" response: Not yet; a request for feedback was sent out recently. (Mail at URL). GENERIC-WHOPICKSMODEL "How does the client know which security policies the RD supports?" response: The client can only expect any level of trustworthiness if there is a claim to that in the RD's credentials. Typically, though, that claim will not be encoded there, but implied. For example, when configuring an application that relies authenticated endpoint names, then telling the application to use the RD authenticated via PKI as URL should only be done if the configurator is sure that URL will do the required checks on endpoint names. Some clarification has been added in URL GENERIC-SUBJECT "Section 7.1 says: '... can be transported in the subject.' -- where precisely?" response: That text was only meant to illustrate to the reader what such a policy could contain, not to set one (which would require more precision). It has been made more explicit that this is merely setting the task for the policies. As an example, some more precision is given by referring to SubjectAltName dNSName entries. Changes in URL (If you have read up to this point, please continue reading the follow-up mails addressing the individual reviewer's points.)

Revised text:
8.3. Services that run over UDP unprotected are vulnerable to unknowingly  <ins> amplify and distribute a DoS attack as UDP does not require return routability check.  Since RD lookup responses can be significantly larger than requests, RDs are prone to this. </ins> RFC7252 describes this at length in its Section 11.3, including some mitigation by using small block sizes in responses.  The upcoming I- a row is way below that because only the colliding node(s) will retry). <ins> Security considerations: Shorten amplification mitigation by removing the references to earlier cases of DDoS amplification, and by removing redundancies between the problem introduction and the description of how an RD could become part of the problem. </ins> changes from -24 to -25 Large rework of section 7 (Security policies)