Re: [secdir] Review of draft-ietf-marf-dkim-reporting-11
Barry Leiba <barryleiba@computer.org> Fri, 09 March 2012 03:02 UTC
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From: Barry Leiba <barryleiba@computer.org>
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Cc: "secdir@ietf.org" <secdir@ietf.org>, "iesg@ietf.org" <iesg@ietf.org>, "draft-ietf-marf-dkim-reporting.all@tools.ietf.org" <draft-ietf-marf-dkim-reporting.all@tools.ietf.org>
Subject: Re: [secdir] Review of draft-ietf-marf-dkim-reporting-11
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> The presence of the DNS record that indicates willingness to accept > reports opens the recipient to abuse. In particular, it is possible > for an attacker to attempt to cause a flood of reports toward the > domain identified in a signature's "d=" tag in one of these ways: > > 1. Alter existing signatures by adding an "r=y" tag (and possibly > altering the "d=" tag to point at the target domain); > > 2. Add a new but invalid signature bearing an "r=y" tag and a "d=" > tag pointing at the target domain; > > 3. Generate a completely new message bearing an "r=y" tag and a "d=" > tag pointing at the target domain. > > Implementers are therefore strongly advised not to advertise that DNS > record except when reports desired, including the risk of receiving > this kind of attack. > > Positive caching of this DNS reply also means turning off the flow of > reports by removing the record is not likely to have immediate > effect. A low time-to-live on the record needs to be considered. > > How does that look? And I've now seen it in context, in the -12 version. Some typos in there, but we'll let the RFC Editor sort it out. But... You're going to hate this, but I think the copious new text in section 8.2 really wants another paragraph. In between the three numbered items and this: Implementers are therefore strongly advised not to advertise that DNS record except when reports desired, including the risk of receiving this kind of attack. ...I'd like to see an extreme-case (but a very-possible-case) example, thus: Consider, for example, the situation if someone should send out a multi-million-message spam run, and include in the messages a fake DKIM signature containing "d=example.com; r=y". It won't matter that those signatures couldn't possibly be real: each will fail verification, and any implementations that support this specification will report those failures, in the millions and in short order, to example.com. I don't think the text that's there lays out the scary possibilities clearly enough. I think something like this does. Barry
- [secdir] Review of draft-ietf-marf-dkim-reporting… Tero Kivinen
- Re: [secdir] Review of draft-ietf-marf-dkim-repor… Murray S. Kucherawy
- Re: [secdir] Review of draft-ietf-marf-dkim-repor… Tero Kivinen
- Re: [secdir] Review of draft-ietf-marf-dkim-repor… Murray S. Kucherawy
- Re: [secdir] Review of draft-ietf-marf-dkim-repor… Barry Leiba
- Re: [secdir] Review of draft-ietf-marf-dkim-repor… Murray S. Kucherawy
- Re: [secdir] Review of draft-ietf-marf-dkim-repor… Tero Kivinen
- Re: [secdir] Review of draft-ietf-marf-dkim-repor… Murray S. Kucherawy