On Thursday, March 14, 2024 12:24:50 PM EDT Scott Kitterman wrote: > On Thursday, March 14, 2024 11:44:22 AM EDT Todd Herr wrote: > > Colleagues, > > > > Issue 135 is open for the subject topic. Please add your thoughts to this > > thread and/or to the issue in Github. > > > > Thank you. > > I'd suggest we discuss where to say it first. I think the right place is > security considerations, which starts: > > 11. Security Considerations > > This section discusses security issues and possible remediations > (where available) for DMARC. > > I think there are two, related questions here: > > One is the risk associated with which I'll call a false pass from one of the > underlying authentication mechanisms. > > The other is the risk associated with using DMARC results for positive > associations (as BIMI does). Even absent third party considerations, all it > takes is one compromised user account and forged messages can get a DMARC > pass. DMARC was designed to identify "bad" mail, not certify any kind of > goodness. > > I think both of these should be addressed as part of this issue in Security > Considerations.
It seems to me that, to the extent we are going to address this issue, there is agreement that Security Considerations is appropriate. Here's proposed text: 11.X External Mail Sender Cross-Domain Forgery Both of the email authentication methods which underlie DMARC fundamentally provide some degree of assurance that an email was transmitted by an MTA which is authorized to do so. SPF policies just map domain names to sets of authorized MTAs [ref to RFC 7208, section 11.4]. Verified DKIM signatures indicate that an email was transmitted by an MTA with access to a private key that matches the published DKIM key record. When Domain Owners authorize mail to be sent by sources outside their Administrative Management Domain there is a risk that an overly permissive source may send mail which will, as a result, receive a DMARC pass result that was not, in fact, authorized by the Domain Owner. These false positives may lead to issues with systems that make use of DMARC pass results to indicate a message is in some way authentic. They also allow such unauthorized senders to evade the Domain Owner's requested message handling for authentication failures. The only method to avoid this risk is to ensure that no overly permissive sources can successfully DKIM sign the domain's mail or transmit mail which will evaluate as SPF pass. If there are non-DMARC reasons for a domain owner to include a permissive source in a domain's SPF record, the source can be excluded from DMARC consideration by using the '?' qualifier on the SPF record mechanism associated with that source. Scott K _______________________________________________ dmarc mailing list dmarc@ietf.org https://www.ietf.org/mailman/listinfo/dmarc
