Re: [OAUTH-WG] [apps-discuss] Apps Area review of draft-ietf-oauth-v2-threatmodel-01

Igor Faynberg <> Mon, 20 February 2012 22:47 UTC

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Subject: Re: [OAUTH-WG] [apps-discuss] Apps Area review of draft-ietf-oauth-v2-threatmodel-01
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Yet another


On 2/20/2012 5:19 PM, André DeMarre wrote:
> +1 for keeping the rationale easily accessible in non-normative
> security documents. Doing so is great for everyone, implementors and
> spec authors alike. Security can be very nuanced, and some
> countermeasures are easy to overlook. Also, being transparent with
> security rationale encourages people to challenge the countermeasures
> that are recommended or built into the spec. If back references help
> us accomplish that, we should embrace them.
> Regards,
> Andre DeMarre
> On Sun, Feb 19, 2012 at 9:16 AM, Torsten Lodderstedt
> <>  wrote:
>> Hi Tim,
>> I just submitted the revised version of the OAuth 2.0 security document
>> ( This
>> revision should address the issues you raised in your AppsDir review. We
>> especially removed all normative language from the document.
>> We took the liberty to leave the back references in Section 5. We consider
>> this back references to section 4 a valuable information for implementors
>> since they justify the particular countermeasure. All to often security
>> considerations are given without the corresponding rationales. And without a
>> justification, the "unconvinced" implementor may tend to ignore or
>> underestimate the respective controls.
>> regards,
>> Torsten.
>> Am 23.01.2012 22:47, schrieb S Moonesamy:
>>> The following is the AppsDir review performed by Tim Bray.  It would be
>>> appreciated if a reply is sent to Tim Bray with a copy to the apps-discuss
>>> mailing list.
>>> I have been selected as the Applications Area Directorate reviewer for
>>> this draft (for background on appsdir, please see
>>> Please resolve these comments along with any other Last Call comments
>>> you may receive. Please wait for direction from your document shepherd
>>> or AD before posting a new version of the draft.
>>> Document: draft-ietf-oauth-v2-threatmodel-01
>>> Title:  OAuth 2.0 Threat Model and Security Considerations
>>> Reviewer: Tim Bray
>>> Review Date:  Jan 23, 2012
>>> Summary: This needs some more editorial work, but is basically sound.
>>> It's not clear, though, whether it wants to be an Informational RFC or
>>> not; the use of RFC2119 language needs special attention.  I think a
>>> few of the "minor issues" are worthy of a little bit more work in
>>> another draft.
>>> Major Issues:
>>> The use of 2119 MUST/SHOULD/etc doesn't seem fully thought through.  I
>>> normally wouldn't expect a "threat model" to include normative text.
>>> The basic idea would be to say "Here is an enumeration of the threats,
>>> and here are the tools available to OAUTH2 implementors to meet them."
>>>   I was impressed by the enumeration, which seemed very complete and
>>> well thought through. But the usage of 2119, which makes statements
>>> normative, seems inconsistent.  I can think of 2 ways to address this:
>>> 1. Remove all the 2119 words, so this document isn't normative, and
>>> publish it as an Informational RFC
>>> 2. Go through and clean up the 2119 language so it's used
>>> consistently; then this becomes a normative document.
>>> This is going to affect the references to this document from other
>>> I-Ds in the OAuth suite, which are currently in last call.
>>> Here are all the section-numbered notes enumerating my issues around
>>> 2119, as I encountered them:
>>> Section 2.3, I'm a little confused about the use of RFC2119 MAY in a
>>> threat analysis.  When you say "The following data elements MAY be
>>> stored or accessible...", Is this saying that "The OAuth2 RFC says
>>> that the following data elements MAY be..." or is it saying something
>>> else. I don't think there's anything seriously wrong here, but a bit
>>> more explanation might be in order.  I note a comparative absence of
>>> 2119-ese in section 5 describing countermeasures, where one would
>>> expect to find it.
>>> Also in 4.3.1, first bullet point, there's "Authorization servers MUST..."
>>> Also in:,,, 4.6.*,,
>>> Related: "SHALL"?! in 4.6.3
>>> Adding to the concern, there is use of lower-case "must"; note 2nd&
>>> 3rd bullet points in 4.4.3, which use "MUST" and "must" respectively.
>>> Minor Issues:
>>> 4.1.2 first attack: It says "An attack may obtain the refresh tokens
>>> issued to a web server client." This needs to be clearer... a "Web
>>> server client" can be a browser or a native app.  Do you mean, "the
>>> refresh tokens issued by the web server to multiple clients?"
>>> 4.1.2 last attack.  In the case where a device is cloned, wouldn't
>>> "Utilize device lock to prevent unauthorized device access" still be a
>>> countermeasure?  In many devices, such cloning would carry along the
>>> user's device-lock settings.
>>> 2nd bullet.  The explanation of why this wouldn't work for
>>> native clients wasn't comprehensible to me.  I'm suspicious of any
>>> such claims because I can emulate most things a browser can do in a
>>> mobile client.  Perhaps this would be obvious to someone who is an
>>> OAuth2 implementor.
>>> I think where it says "iFrame" it might mean "WebView", i.e. a
>>> Web Browser control embedded in the native app.  If that's not what it
>>> means, I don't understand what it's saying.  If this is true, then the
>>> second bullet point is probably wrong.
>>> 4.6.6 1st bullet.  I'm not convinced that the Cache-Control header
>>> will *ensure* that a client protects information properly.  Should say
>>> something like "minimize the risk that authenticated content is not
>>> protected"
>>> 5.* The enumeration, for some but not all of the countermeasures in
>>> this section, of the threats against which this is a countermeasure,
>>> reduces readability and, unless it's generated automatically from the
>>> underlying source, is redundant information, which is unlikely to be
>>> consistent between sections 4 and 5, and adds difficulty to
>>> maintenance of this document without adding much value.  I'd just wipe
>>> all these bullet lists out.  If it's generated automatically it's less
>>> damaging, but still reduces readability.  In the current draft, this
>>> is there for some countermeasures but absent for others.  Another good
>>> reason to just take it out.
>>> Device identifiers are very tricky.  It's correct that IMEI is
>>> not adequate, but there are ways to do it without SMS.  For more, see
>>> 5.3.4 Surely a little more could be said about device lock.  On a
>>> typical modern phone, "device lock" options include PINs, passwords,
>>> "face recognition" and so on.  These are *not* equal in their level of
>>> security they provide.
>>> Nits:
>>> Formatting is lousy.  There are notations, including ** and _whatever_
>>> that I'm not familiar with in the RFC context.
>>> Section 1.0: s/in-built into/built into/
>>> 2.1, last bullet point: "An example could by a..." s/by/be/
>>> 2.2, 1st bullet point s/eaves drop/eavesdrop/
>>> 2.3, 1st para, s/treat/threat/
>>> 2.3.1, last bullet, "per authorization process".  Adjectival phrases
>>> should be hyphenated: "per-authorization process"
>>> 2.3.3, last bullet, ditto
>>> 3.1, 1st para, "all kinds of tokens" should be "many kinds of tokens"
>>> 3.1, 2nd para, should be ; not , after "within the authorization server"
>>>       s/protected/protect/
>>>       s/different system/different systems/
>>> 3.4 1st para, s/intermediary/intermediate/
>>>       list item 1. s/short-living/short-lived/
>>> 3.5 s/malicious client/malicious clients/
>>> 3.7 top of page 12, what is the underscore notation _client_id_ mean?
>>> I'm not familiar with this in the RFC context.
>>>   1st bullet point: s/token/token's/
>>>   2nd bullet point, multiple issues, 1st sentence should be " the
>>> initial authorization and issuance of a token by an end-user
>>>      to a particular client, and subsequent requests by this client to
>>>      obtain tokens without user consent (automatic processing of repeated
>>>      authorization)
>>>   halfway down page 13, s/insures/ensures/
>>>              s/validates the clients/validates the client's/
>>> 4. first sentence, s/this sections/this section/
>>> 4.1.2 first para, the last sentence is confusing. How about: "Before
>>> enumerating the threats, here are some generally applicable
>>> countermeasures:"
>>> 4.2.4 2nd bullet s/could not be/can not be/
>>> 4.3.3 1st bullet, capitalized phrase "Confidentiality of Requests" - I
>>> assume that's supposed to be a hyperlink to one of the 5.* sections?
>>> last bullet, s/referee/referrer/ - also, should note that the
>>> referrer header may contain an Authorization code in a ?a=b style
>>> argument
>>> first bullet, "can be employed" is inconsistent with style of
>>> rest of doc
>>> first 2 bullets have un-labeled links.
>>> 1st bullet s/authentication/authenticate/
>>> 2nd bullet s/mean/means/
>>> 2nd bullet s/tokens/token's/
>>>, 2nd para, s/requisiete/requisite/ s/embbed/embed/
>>>, 3rd bullet, s/aibility/ability/
>>>, toward bottom of page 30, s/e.t.c./etc./
>>> I think the href to needs to be turned into
>>> an IETF-style reference
>>> 4.4.2 " since HTTP user agents do not send fragments server requests."
>>> What you mean to say is "Since HTTP user agents do not send the
>>> fragment part of URIs to HTTP servers."
>>> s/browser/browser's/
>>> s/consider to not store/refrain from storing/
>>> 5.* s/may consider to $(verb)/may consider $(verb)ing/
>>> 5.1.6 Needs some sort of sentence structure
>>> 5.3.2 Needs some sort of sentence structure; or is this intended just
>>> to be a title, with 5.3.3 etc nested under it?
>>> _______________________________________________
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