OAuth 2.0 Threat Model and Security Considerations
draft-ietf-oauth-v2-threatmodel-08

[Ballot comment]
1) The base spec (https://datatracker.ietf.org/doc/draft-ietf-oauth-v2/) is now a "framework".  Not sure that should also be reflected in this draft.

2) It might be worth changing the note in s1 to a s1.1 and title it "disclaimer".

3) I'm thinking this might

4) s4.2.1: Often times we do the whole MTI (mandatory to implement) is not MTU (mandatory to use), but here it sounds like you really want to say:

Authorization servers should consider such attacks when developing
services based on OAuth, and should require *the use of*
transport-layer
security for any requests where the authenticity of the
authorization server or of request responses is an issue (see
Section 5.1.2).

5) Nits:

s4.1.2: r/side/site

s4.2.3: r/clients or unless/clients unless ?

[Ballot discuss]
Hoping these will be fairly easy to work through.

1) Entirely possible I missed this bit:

My favorite bit in the base spec is this bit:

    ... "leaves a few required components
  partially or fully undefined (e.g. client registration, authorization
  server capabilities, endpoint discovery).  Without these components,
  clients must be manually and specifically configured against a
  specific authorization server and resource server in order to
  interoperate."

s2.3 of this draft says:

  The OAuth protocol leaves deployments with a certain degree of
  freedom how to implement and apply the standard.

and then goes on to talk about collocating servers. 

Is that fact that there's a list, which probably includes a whole lot more than those three things listed in the base spec, worth some additional text?  I guess there's the note in s1, but shouldn't the fact that the framework isn't entirely specified be specifically called out?

2) s4.1.1: When you say "a particular client" in the 1st attack (from source code or binary) is that the attacker got my particular client's secret or that the attacker got client X's secret and everybody who uses client X now has no secret (I'm thinking like 1M people using a client that they've downloaded)?  If it's the latter, it'd be better to clarify/amplify that a bit.

3) While processing the OAuth framework draft, the discussion around the SHOULD in s3.1.2.1 (Endpoint Request Confidentiality) basically came down to folks not really wanting to implement TLS for this bit.  Basically, if we forced the MUST most folks would have ignored it.  I think (correct me if I'm wrong) that this correlates to the discussion in s4.4.1.5/6 of this draft where the draft says the "client should point to a HTTPS ..." Are we saying for all those clients there's no countermeasure?

[Ballot comment]
1) The base spec (https://datatracker.ietf.org/doc/draft-ietf-oauth-v2/) is now a "framework".  Not sure that should also be reflected in this draft.

2) It might be worth changing the note in s1 to a s1.1 and title it "disclaimer".

3) I'm thinking this might

4) s4.2.1: Often times we do the whole MTI (mandatory to implement) is not MTU (mandatory to use), but here it sounds like you really want to say:

Authorization servers should consider such attacks when developing
services based on OAuth, and should require *the use of*
transport-layer
security for any requests where the authenticity of the
authorization server or of request responses is an issue (see
Section 5.1.2).

5) Nits:

s4.1.2: r/side/site

s4.1.2: (aside no action required) if the attacker can overcome the web application, then I'd say the standard web server protection measures aren't very good ;)

s4.2.3: r/clients or unless/clients unless ?

[Ballot comment]
I think having all of this analysis written down is fine, but I'm not convinced this document will end up being useful. It's quite a bit of information in a form that I'm not sure any implementer will be able to get through and act on. But I certainly don't think we should dispose of all of this information. I just wish there was more meat on these bones. In particular:


Introduction:

  Note: This document cannot assess the probability nor the risk
  associated with a particular threat because those aspects strongly
  depend on the particular application and deployment OAuth is used to
  protect.

While this may be generally true, I do think it's possible to assess some sort of relative risk between this massive list of threats. I find the lack of such an assessment, along with the sheer volume of this document, makes the document significantly less useful than it might be.

A few small comments on some earlier bits of the document that I hope will be useful for edits throughout the document, but if they don't get done, the world will not end:

3.7 says:

  Deployment-independent client_id with pre-registered redirect_uri and
  with client_secret  This is an option for native applications only,
      since web application would require different redirect URIs.  This
      category is not advisable because the client secret cannot be
      protected appropriately (see Section 4.1.1).
     
You bet it's not advisable. :-) And I think that itself is a fine thing to say. But then 4.1.1 goes on to say:

  Attack: Obtain Secret From Source Code or Binary:

  This applies for all client types.

It does? I thought it only applied to client types that are pre-configured with client secrets? Then in the Countermeasures, it says:

  Countermeasures:

  o  Don't issue secrets to public clients or clients with
      inappropriate security policy - Section 5.2.3.1

OK, but that's effectively "don't use this deployment model", right?

  o  Public clients require user consent - Section 5.2.3.2

That's worded badly. Do you mean, "Require user consent" as the counter measure?

  o  Use deployment-specific client secrets - Section 5.2.3.4

Isn't this identical to the first bullet?

  o  Client secret revocation - Section 5.2.3.6

That's not worded as a countermeasure. Do you mean, "Routinely revoke client secrets"? How can you do secret revocation without disabling entire implementations?

In general, throughout the document, there are lots of things labeled "countermeasures" that are worded in noun form instead of verb form.  For example, in 4.1.2 you have listed as a countermeasure:

  o  Limited scope tokens - Section 5.1.5.1

It would be much clearer if these were all reworded as the action one should take, not the topic area regarding the counter measure.

(If I have additional time, I'll add to this list of comments.)

[Ballot comment]
On the basis of a quick scan of the text I can see no Routing issues with this document and am thus taking a position of no objection.

IANA has reviewed draft-ietf-oauth-v2-threatmodel-06, which is currently
in Last Call, and has the following comments:

IANA understands that, upon approval of this document, there are no
IANA Actions that need completion.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
Cc: oauth@ietf.org
Reply-To: ietf@ietf.org
Subject: Last Call:  (OAuth 2.0 Threat
Model and Security Considerations) to Informational RFC


The IESG has received a request from the Web Authorization Protocol WG
(oauth) to consider the following document:
- 'OAuth 2.0 Threat Model and Security Considerations'
  as Informational RFC

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2012-07-11. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  This document gives additional security considerations for OAuth,
  beyond those in the OAuth specification, based on a comprehensive
  threat model for the OAuth 2.0 Protocol.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-oauth-v2-threatmodel/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-oauth-v2-threatmodel/ballot/


No IPR declarations have been submitted directly on this I-D.

PROTO writeup for draft-ietf-oauth-v2-threatmodel-05

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

This documents security considerations for the OAuth framework that go
beyond the level of considerations that are reasonable to include in
the protocol documents themselves.  Those documents have informative
references to this one, and this is intended to provide additional
information for implementation and deployment of OAuth.  The intended
status is Informational, and the document header says so.

(2) The IESG approval announcement includes a Document Announcement
Write-Up. Please provide such a Document Announcement Write-Up. Recent
examples can be found in the "Action" announcements for approved
documents. The approval announcement contains the following sections:

Technical Summary

  Relevant content can frequently be found in the abstract
  and/or introduction of the document. If not, this may be
  an indication that there are deficiencies in the abstract
  or introduction.

This document gives additional security considerations for OAuth,
beyond those in the OAuth specification, based on a comprehensive
threat model for the OAuth 2.0 Protocol.
 
The document:
o  Documents any assumptions and scope considered when creating the
  threat model.

o  Describes the security features in-built into the OAuth protocol
  and how they are intended to thwart attacks.

o  Gives a comprehensive threat model for OAuth and describes the
  respective counter measures to thwart those threats.
 
Working Group Summary

  Was there anything in WG process that is worth noting? For
  example, was there controversy about particular points or
  were there decisions where the consensus was particularly
  rough?

This document began life as a working document for the development of
a Security Considerations section of the base OAuth protocol document.
It quickly became far too large for that purpose, and at IETF 80 a
design team was set up to extract the key points for a proper Security
Considerations section, leaving the remainder for this Informational
document.

Throughout the development, the goal has been to include as much as
possible.  There's been some discussion of whether this has resulted
in a document that's too long to be practical.  And that concern has
resulted in some pushback at the end of its life cycle, resisting the
addition of new material that seemed non-specific to OAuth.  There
have nevertheless been some compromises made, as some participants
considered it important in a few cases to highlight threats that apply
to services in general, but that might be falsely construed either as
not applying to OAuth, or as being mitigated in some way by OAuth.

Document Quality

  Are there existing implementations of the protocol? Have a
  significant number of vendors indicated their plan to
  implement the specification? Are there any reviewers that
  merit special mention as having done a thorough review,
  e.g., one that resulted in important changes or a
  conclusion that the document had no substantive issues? If
  there was a MIB Doctor, Media Type or other expert review,
  what was its course (briefly)? In the case of a Media Type
  review, on what date was the request posted?

In the end, we have a document that's thorough and well written, and
that represents the consensus of the working group, with a liberal
view toward inclusion.  The authors have already noted, in the
acknowledgments, key contributors and reviewers.

Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

Barry Leiba is the document shepherd.  Stephen Farrell is the responsible AD.

(3) Briefly describe the review of this document that was performed by
the Document Shepherd.  If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

The document has had good review and is ready for publication.  The
shepherd has reviewed several versions, both pre- and
post-working-group-adoption, and has reviewed the final version
carefully.  A few changes were made during shepherd review, and the
shepherd has no issues with the document.

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No.

(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

The document has had thorough review from the OAuth community,
including a number of participants from the IETF Applications and
Security areas.  The shepherd is happy with the level of review.

(6) Describe any specific concerns or issues that the Document Shepherd
has with this document that the Responsible Area Director and/or the
IESG should be aware of? For example, perhaps he or she is uncomfortable
with certain parts of the document, or has concerns whether there really
is a need for it. In any event, if the WG has discussed those issues and
has indicated that it still wishes to advance the document, detail those
concerns here.

No concerns.

(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

There are no IPR disclosures related to this document, and no one
involved with the document is aware of any issues in this regard.

(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

See 7.

(9) How solid is the WG consensus behind this document? Does it
represent the strong concurrence of a few individuals, with others
being silent, or does the WG as a whole understand and agree with it?

The working-group consensus is solid; the group as a whole understands
and agrees with it.

(10) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise the areas of conflict in separate
email messages to the Responsible Area Director. (It should be in a
separate email because this questionnaire is publicly available.)

No.  As with any document of this nature, there are those who think
other threats and scenarios should be included, and some are
necessarily left out.  That said, we believe there's no "extreme
discontent", and that enough is included so that everyone is
reasonably happy that the topic is thoroughly covered.

(11) Identify any ID nits the Document Shepherd has found in this
document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

There are a couple of things called out by idnits.  The ones about
FQDNs and IP addresses are not applicable.  There is a remaining
citation to RFC1750 that needs to be changed to RFC4086, and we should
put in an RFC Editor note for now.

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

None required.

(13) Have all references within this document been identified as
either normative or informative?

Yes.

(14) Are there normative references to documents that are not ready for
advancement or are otherwise in an unclear state? If such normative
references exist, what is the plan for their completion?

This document depends upon and normatively references the OAuth v2
base specification, which is in IESG Evaluation.

(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in the
Last Call procedure.

No.

(16) Will publication of this document change to the status of any
existing RFCs? Are those RFCs listed on the title page header, listed
in the abstract, and discussed in the introduction? If the RFCs are not
listed in the Abstract and Introduction, explain why, and point to the
part of the document where the relationship of this document to the
other RFCs is discussed. If this information is not in the document,
explain why the WG considers it unnecessary.

This document does not change the status of any other document.

(17) Describe the Document Shepherd's review of the IANA considerations
section, especially with regard to its consistency with the body of the
document. Confirm that all protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

No actions are requested of IANA, and the IANA Considerations section
says so.

(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

None.

(19) Describe reviews and automated checks performed by the Document
Shepherd to validate sections of the document written in a formal
language, such as XML code, BNF rules, MIB definitions, etc.

No formal language is used in this document.