Thank you, Murray, for your extremely thorough review. My current plans are to produce a new rev by the end of October based on these comments and Tim's review.
On Sun, Sep 29, 2024 at 5:17 PM Murray S. Kucherawy <[email protected]> wrote: > Colleagues, > > This is my AD evaluation for DMARCbis. I've taken the liberty of > preparing it even though the shepherd writeup is not yet uploaded and the > chairs have not yet formally requested publication. > > There's a Google document to which everyone has "view" access at the link > below for the details as there's a large number of aesthetic tweaks I made > (missing or mismatched quotes, etc.) and minor text suggestions, but the > non-trivial things I'd like to raise and possibly discuss are laid out > here. If you're not one of the document editors, you probably don't need > the Google document, but here it is anyway if you're curious: > > > https://docs.google.com/document/d/14Mz005MU2lIIL0zOZxgdkOFprW57clrsmumToJvwVMU/ > > I recognize that this document has WG consensus, and my own views about > some things are in the rough. Where I appear to be challenging consensus, > look at it more like I'm trying to help you make the WG's position less > likely to meet obstruction. I'm not blocking it from moving forward. > > It was a long road to get here, I realize. There are still some steps we > need to get through before this can be published, and it's unclear how > smooth of a ride that's going to be. There will almost certainly be more > feedback. Let's please try to build or at least preserve whatever momentum > we have left to get it across the finish line. More on this later. > > Here we go, in top-down (i.e., not priority) order: > > In Section 2.1, under "High-Level Goals", there's a bullet that reads thus: > > "Minimize implementation complexity for both senders and receivers, as > well as the impact on handling and delivery of legitimate messages." > > Given the collision with indirect mail flows, which I don't think this > document actually improves relative to RFC 7489, do we feel like we met > this goal, at least the part after the comma? Should we revise this so we > don't draw fire for a failure here? > > In Section 2.4, "Out Of Scope", there's this bullet: > > "Reporting or otherwise evaluating other than the last-hop IP address;" > > ...which reminds me that ARC is in an unresolved state. Is the plan to > ship DMARCbis without any particular reference to its use and "Update" it > in later? There's another reference to ARC later in the document as well. > > In Section 3.2.8, "MTA" is defined as "Mail Transport Agent", but we also > import definitions from RFC 5598, which defines it as "Message Transfer > Agent". We should probably match that. > > In Section 3.2.10, two things: > > * Did we ever discuss RFC 7505 in this context? > > * This is the first place I noticed that in some places throughout the > document (and there are many instances), a reference to another RFC looks > like the usual "[RFCxxxx]", but in others it's the more verbose "RFCxxxx, > <title>". We should pick one or the other and use it throughout, and I > suggest that the former is far more common. > > Section 3.2.12 is the first reference to PSD. About PSD in general: This > document introduces this concept, as a significant change since RFC 7489. > Appendix C identifies it as a major change, which is good, but I'm > wondering if somewhere we might want additional text that describes the > likely interaction between Domain Owners relying on PSD and Receivers > relying on the old PSL way of doing things, or vice versa. Are there any > interoperability concerns? > > Section 3.2.15 refers to "messages related to another operator's domain". > If there's an example of such an arrangement in the appendices, this is one > spot where I felt I'd like a more complete description so a forward > reference would be helpful for illustration. > > In Section 4.4.1, I thought it might be helpful to make an explicit > statement that there is no currently accepted common mechanism for > declaring a third-party relationship in terms of signing and DMARC > evaluation, though several have been considered. Section 4.4.2 needs the > same thing about SPF, so maybe an additional subsection that says the same > about both would be better. > > Section 4.5 says: > > DMARC Policy Records are stored as DNS TXT records in subdomains named > "_dmarc". > > Are those subdomains? Aren't they just records in the domain? I suspect > DNS people might get picky here. > > In Section 4.6, the SHOULD needs justification. > > In Section 4.7, just out of curiosity, how much have we observed use of > the "fo" tag in the wild? > > Same section, for "np", we might want to include a link to where > "non-existent domain" is defined in the DMARC context. > > Same section, for "psd", in the "y" block, there's use of the term "policy > domain" for the first time in this document. I'm thinking it needs a > formal definition somewhere (or just spell it out here). > > Same section, again for "psd", in the "u" block, we say "There is no need > to explicitly publish psd=u in a DMARC Policy Record." Do we need to say > that when we already say it's the default? > > Same section, for "rua" and for "ruf", instead of "URIs not supported...", > I think we want "URI schemes not supported ..." > > Same section, for "t", in the "y" block, we find the first reference to > the idea of From field rewriting. Does this need treatment or a reference > somewhere before we run into it here? > > In Section 4.8, I think there's an ABNF ambiguity in that "dmarc-record" > ends with *WSP, but so does the optional "dmarc-sep" right before it. > > Section 4.10 is the first place where the PSL is mentioned. We might want > to include a forward reference to Appendix C here; left by itself, it > assumes the reader has that context. > > Also in Section 4.10, I don't know what the purpose of Step 3 is. > > Same section, I think there's a problem with Step 7. If I'm following > this correctly, this query might return a single record containing "psd=n" > and there might still be one from Step 2 that contains "psd=y". This test > then fails because it's not true that "a single record remains", so the > algorithm continues. Steps 6, 7, and 8 are then repeated up to the limit > at which point the algorithm stops with two or more answers in the set. Is > that what's intended here? What does a filter do with that? > > Section 4.10.1 says: > > "Note: PSD policy is not used for Organizational Domains that > have published a DMARC Policy Record. Specifically, this is not > a mechanism to provide feedback addresses (rua/ruf) when an Organizational > Domain has declined to do so." > > So back in Section 4.7, the formal part, should we say expressly that > "psd=y" MUST NOT be used with the "rua" and "ruf" tags? > > Section 5.1.1, regarding SPF, says: > > "... SHOULD be constructed to ensure that only those authorized sources > can get an SPF pass verdict." > > Why is this only SHOULD when it's MUST for DKIM (Section 5.1.2)? > > I think Section 5.3.1 should say more about multi-valued From and what > MUAs tend to do with it. Otherwise, this almost says "If you want to > bypass DMARC, just use a multi-valued >From field." Are attackers not > incentivized to try? > > In Sections 5.3.3 and 5.3.7, the SHOULDs need to be justified. The one in > 5.3.9 is a little better, but it could say more. > > The second paragraph of Section 5.4 is significant. I think Section 10 > should contain a reference to it, or maybe this paragraph should move there > and be replaced by a reference to that. > > Same section, we have "important that Mail Receivers not reject messages > solely because of a published policy of "reject", ..." Does this warrant a > SHOULD NOT? > > Section 6 introduces, but does not define, the terms "PSD DMARC" and > "org-level". > > In Section 7.1, the two M3AAWG links need to become informative references. > > Section 7.2 strikes me as something that isn't likely a novel discussion, > so is there any other DNS document we can think of where we can reference > the topic? > > At the bottom of Section 7.3: RFC 7372 introduced enhanced status codes > related to mail authentication; should we consider registering some for > DMARC? > > A note to Tim: I think the shepherd writeup needs to call out that the > material in Section 7.5 was controversial, though the WG did reach > consensus on the text that's there. > > Same section: I also think -- and this is probably my most significant > piece of feedback for the WG -- that we need to include some discussion of > the fact that we are knowingly advancing to the Standards Track something > that has serious and well described interoperability concerns. This is > being done because (give reasons here). This could go here or in its own > section (definitely not in an appendix). RFC 6377 is available as a > reference to describe some of the disruption. Just as with the principle > behind Security Considerations sections, I think it's more important to > highlight that we know there are problems, but believe this is worth > publishing at Proposed Standard anyway. > > Same section: We're saying receivers MUST NOT reject based solely on the > DMARC result. I feel like we're pushing the interoperability problem onto > receivers here. What advice do we have for them around how to go about > doing this? What properties of a message should they be looking at to head > off this problem? Is anyone successfully doing this today? > > In several spots in Section 8, the text talks about creating a registry, > but the registry already exists. For each, we should instead say that RFC > 7489 created the registry, but all existing references to that document > should now point here. > > Section 10.4 talks about display name attacks, and I wonder if we have any > (even vague) figures that compare the display name problem to the direct > domain attack problem. If we think this is going to take out a small > portion of the problem, or if we think the display name attack will grow as > a result, we should probably say so. > > The second paragraph of Section 10.8 took me several times to read and > parse. Maybe an example would help. Same sort of remark about the fourth. > > Section 10.8 also talks about "periodically checking the DMARC Policy > Records, if any, of PSDs" but doesn't talk about how one might achieve > knowledge of where they are. Is this just caching of the ones you've > discovered? > > In Appendix A.1, S/MIME is RFC 8551. > > In Appendix A.3, DomainKeys is RFC 4870. > > Appendix A.6, third paragraph, third sentence, total parse failure. > > Appendix C.1, a correction: RFC 7489 has no IETF category or status at > all. It's an informational RFC that was not a product of the IETF. In > fact the only IETF review it got was the IESG confirming that it doesn't > conflict with any work in the IETF already in progress. > > -MSK > _______________________________________________ > dmarc mailing list -- [email protected] > To unsubscribe send an email to [email protected] > -- Todd Herr | Technical Director, Standards & Ecosystem Email: [email protected] Phone: 703-220-4153 This email and all data transmitted with it contains confidential and/or proprietary information intended solely for the use of individual(s) authorized to receive it. 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