Re: [DNSOP] Validating responses when following unsigned CNAME chains...

Brian Somers <bsomers@opendns.com> Thu, 30 April 2020 03:39 UTC

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From: Brian Somers <bsomers@opendns.com>
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Date: Wed, 29 Apr 2020 20:38:59 -0700
Cc: Brian Somers <bsomers@opendns.com>, Michael StJohns <msj@nthpermutation.com>, "dnsop@ietf.org WG" <dnsop@ietf.org>
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To: Shumon Huque <shuque@gmail.com>
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Subject: Re: [DNSOP] Validating responses when following unsigned CNAME chains...
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On Apr 29, 2020, at 7:12 PM, Shumon Huque <shuque@gmail.com> wrote:
> Mike, perhaps there was some confusion on this point 12 years ago, but
> deployed validator code all agree on what the state is. I encourage 
> implementers to confirm (or correct me if I misstate something).

Absolutely.  You only get the AD bit if *ALL* RRs in the Answer & Auth
sections are validated as secure.

….
> : If you've got an securely insecure (e.g. delegation was to an insecure 
> : zone at some point) CNAME that points into a secure zone, I would say 
> : your result is probably Bogus  or Unsecure as you haven't any way to 
> : evaluate trust.  I don't think you can bootstrap security this way..
> 
> Deployed validator code says Insecure.. It can't be Bogus, because the validator
> has determined that the CNAME is a demonstrably insecure zone,

Furthermore, the CNAME alias RRset must be validated unless the CD bit is set.
A validating resolver MUST validate and can only return RRsets if they are proven
to be either insecure or secure.  If the aliased RRset is bogus, the answer is
SERVFAIL.

—
Brian