Re: [spfbis] Last Call: <draft-ietf-spfbis-4408bis-19.txt> (Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1) to Proposed Standard

Scott Kitterman <scott@kitterman.com> Wed, 21 August 2013 23:12 UTC

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Subject: Re: [spfbis] Last Call: <draft-ietf-spfbis-4408bis-19.txt> (Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1) to Proposed Standard
From: Scott Kitterman <scott@kitterman.com>
Date: Wed, 21 Aug 2013 19:12:27 -0400
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Mark Andrews <marka@isc.org> wrote:
>
>In message <7917527.VmCQD3a6Q3@scott-latitude-e6320>, Scott Kitterman
>writes:
>> On Wednesday, August 21, 2013 23:32:33 Mark Andrews wrote:
>> > I object to the removal of the SPF record.
>> 
>> This is not a shock.  You were in the rough when we discussed it in
>the WG 
>> too.
>> 
>> > Name servers already have access controls down to the granuality
>> > of TYPE.  If this draft proceeds as currently described it is
>forcing
>> > name server vendors to access controls at the sub TYPE granuality.
>> 
>> It's primarily an issue for applications.  To the DNS, it's exactly
>what it 
>> is, a TXT record.
>
>No.  It isn't.  By overloading TXT you prevent thing like this which
>existed before SPF was even dreamed up.
>
>	update-policy {
>		grant key-one subdomain example.net ANY
>		deny key-two domain example.net SPF
>		grant key-two domain example.net ANY
>	};
>
>	or
>
>	update-policy {
>		grant key-one subdomain example.net ANY
>		grant key-two domain example.net TXT
>	};
>
>Overloading a type is bad on so many levels which is why it was
>argued that SPF needed its own type.  TXT is good for prototyping
>and that is about all.
>
>	update-policy {
>		grant key-one subdomain example.net ANY
>		deny key-two domain example.net TXT/v=spf1
>		grant key-two domain example.net ANY
>	};
>
>	update-policy {
>		grant key-one subdomain example.net ANY
>		deny key-two domain example.net TXT/v=spf1
>		grant key-two domain example.net TXT!v=spf1
>	};

This can be solved other ways.  See my repky to your later message.

>> > With SPF lookup first I can specify the SPF policy using SPF and
>> > leave TXT free for other uses without having to worry about the
>> > records being misinterpeted.
>> 
>> Unless you have some specific reason to be concerned about
>accidentally 
>> starting an unrelated TXT record with "v=spf1 ", I can't imagine you
>don't 
>> have more important things to worry about.  This being a "problem" is
>a great 
>> theory, but it just doesn't happen in practice.
>
>It's about being able to hand someone update control and not having to
>worry about them stuffing up the SPF records.
> 
>> > SPF validators MUST NOT proceed to a TXT lookup on SERVFAIL for
>SPF.
>> > This is similar to not proceeding to A/AAAA lookups on MX lookup
>> > failures.
>> 
>> Except that it's quite common for a SERVFAIL on TYPESPF to occur for
>a domain 
>> that has an actual SPF record due to various operational issues. 
>SERVFAIL on 
>> type SPF doesn't reliably tell you anything about what a type TXT
>lookup would 
>> produce.  So it's similar, but only superficially so.
>
>And the worst that happens is that you let some *additional*
>potentially spoofed email through.  This WG seems to treat this
>as a catastrophic errror when it isn't.  This whole debate is
>because this working group treats not stopping one additional
>forgery as a catastrophic errror.

I prefer to design things for reliability rather than ignore interoperability problems. 

>Note also that it will be the publishing site to blame for having
>a non RFC 1034 compliant server (it didn't respond to SPF queries)
>or misconfigured zone (returns wrong SOA in the negative response 
>which can't happen when they have a SPF record).

Or some firewall in a box in between. Blame is not so easy to determine. 

>> > I would also suggest that there be a sunset date published for the
>> > use of TXT for SPF.
>> 
>> Do you also suggest creation of an Internet police force to enforce
>this?  
>> What would be be mandatory minimum sentence?
>
>You just code the cut off date into the code that does the verification
>and stop making TXT queries.  You code the date into the code that
>checks for missing SPF records and change the complaint.

Is there an example of this kind of approach working? 

Scott K