Re: [secdir] SECDIR review: draft-hammer-hostmeta

Eran Hammer-Lahav <eran@hueniverse.com> Sun, 08 August 2010 06:14 UTC

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From: Eran Hammer-Lahav <eran@hueniverse.com>
To: Kurt Zeilenga <Kurt.Zeilenga@Isode.com>, IETF <ietf@ietf.org>
Date: Sat, 7 Aug 2010 23:15:27 -0700
Thread-Topic: SECDIR review: draft-hammer-hostmeta
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Cc: "draft-hammer-hostmeta@tools.ietf.org" <draft-hammer-hostmeta@tools.ietf.org>, IESG IESG <iesg@ietf.org>, Security Area Directorate <secdir@ietf.org>
Subject: Re: [secdir] SECDIR review: draft-hammer-hostmeta
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Thanks for the review.

I will add these points to the security consideration section, but will keep it as a host level document, not service level. This well-known document is appropriate when looking for host metadata, and application choosing to use it, must consider the implications. By itself, host-meta means very little. Applications need to "buy-into" the document (and spell out how to use it) in order for it to have meaning. When doing so, they must consider its implications.

EHL

> -----Original Message-----
> From: Kurt Zeilenga [mailto:Kurt.Zeilenga@Isode.com]
> Sent: Friday, July 16, 2010 7:18 AM
> To: IETF
> Cc: draft-hammer-hostmeta@tools.ietf.org; Security Area Directorate; IESG
> IESG
> Subject: SECDIR review: draft-hammer-hostmeta
> 
> I have reviewed this document as part of the security directorate's ongoing
> effort to review all IETF documents being processed by the IESG.  These
> comments were written primarily for the benefit of the security area
> directors.  Document editors should treat these comments just like any other
> last call comments.
> 
> I have a number of security-related concerns with this specification.
> 
> First, I'm concerned by assumptions in the document that each of:
> 	http://example.com
> 	http://example.com:8080
> 	https://example.com
> 	https://example.com:8443
> 
> identify resources under the control of same entity.   It is fairly common to
> there to be multiple http/https services running on a single host, each service
> possibly operated by different entities as delegated by the "host"
> administrator.  I think it would be better (from a security perspective) to
> have "service"-level metadata, not "host" level meta data.  That is, make no
> assumption that the above URIs are under control of the same entity, or
> even if so, that it desirable to a single policy/metadata covering multiple
> services.
> 
> And I think it very important to always fetch the meta data from the service
> one is accessing.  The document calls for client to fetch
> https://example.com/.well-known/host-meta even when
> https://example.com:8443 is URI wants policy for.
> 
> Even worse, the document calls for the client to, if the above fetch does not
> produce a "valid" hostmeta document, for the client to fetch
> http://example.com/.well-known/host-meta.  An attacker could easily cause
> https://example.com/.well-known/host-meta to fail to produce a "valid"
> hostmeta document, and serve its own hostmeta document in response to
> the client's http://example.com/.well-known/host-meta, without
> supplanting the https://example.com:8443 service.
> 
> The document fails to discuss such attacks.
> 
> I recommend reworking this document to provide service-level, not host-
> level, metadata.  In particular, the metadata document should always be
> retrieved through the service the client is interested in using, such as by
> fetching "/.well-known/metadata".
> 
> If the authors rather continue pursuing a "host-based" solution, the security
> considerations should include a discussion of the above issues.
> 
> Regards, Kurt