Re: [mile] Secdir review: draft-ietf-mile-5070-bis-22

[[e-mail]]

Hello,

Thanks Robert for the detailed and helpful review.  Inline 

Sent from my iPhone

> On Jun 2, 2016, at 4:51 AM, Alexey Melnikov <[e-mail]> wrote:
> 
> Hi Roman,
> 
>> On 02/06/2016 06:03, Roman D. Danyliw wrote:
>> Hello Robert!
>> 
>> Thanks again for this review.  Comments are inline ...
>> 
>>> -----Original Message-----
>>> From: Robert Sparks [mailto:[e-mail]]
>>> Sent: Monday, May 30, 2016 2:44 PM
>>> To: [e-mail]; [e-mail]; [e-mail]
>>> Subject: Secdir review: draft-ietf-mile-5070-bis-22
>>> 
>>> 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 and WG chairs should treat these comments
>>> just like any other last call comments.
>>> 
>>> Document : draft-ietf-mile-rfc5070bis-22
>>> 
>>> Summary: This document has minor issues that should be addressed before
>>> publication as Proposed Standard
>>> 
>>> This document defines a document format for exchanging information
>>> between operational security teams. It points out standardized mechanisms
>>> for transporting the documents (RFC6545 and RFC6546), to provide
>>> confidentiality, integrity, and authenticity, but does not restrict the use of the
>>> format to within those protocols.  Instead, it provides a generic set of
>>> "Processing Considerations" in section 4, which are augmented by the
>>> Security Considerations in section 9.
>>> 
>>> There are some minor issues with this approach that should be addressed
>>> before publication.
>>> 
>>> 1) The document requires that implementations validate documents against
>>> the schema, and reject any documents that fail validation.  In particular,
>>> Section
>>> 5.2 Item 4 requires rejecting documents with an unrecognized element in a
>>> supported namespace as a syntax error. Section 4.3 requires
>>> implementations to
>>> ->dynamically generate the schema used for validation from IANA
>>> registries<-.
>>> Section 5.2 Item 5 calls out that this dynamic generation has security and
>>> performance implications, but does not describe them, and has a very vague
>>> "SHOULD NOT download schemas at runtime" to guard against them.  I seem
>>> to recall significant discussion in other contexts of the issues with generating
>>> schema from IANA registries at runtime.  Perhaps the ADs can provide
>>> pointers to material generated from those discussions that the group can
>>> reference.
>>> Otherwise, the threats need to be described in more detail, and the
>>> operational complexity of exercising these extension points (particularly
>>> given the requirement to reject documents that do not validate against the
>>> content of the
>>> registries) needs to be spelled out.
>> To this analysis, I'll also add Stephen Farrell's COMMENT (https://www.ietf.org/mail-archive/web/mile/current/msg01885.html) against using validation and the security issues when checking the IANA registry; and that Alexey Melnikov has marked this issue as a DISCUSS (https://datatracker.ietf.org/doc/draft-ietf-mile-rfc5070-bis/ballot/).
>> 
>> To the WG:
>> 
>> Consideration #1
>> ==============
>> 
>> ---[ begin Item #4 of Section 5.2 ]---
>>    4.  Implementations that encounter an unrecognized element in a
>>        supported namespace MUST reject the document as a syntax error.
>> ---[ end Item #4 of Section 5.2 ]---
>> 
>> ** Do we want to weaken the validation requirement in Item #4 of Section 5.2 from MUST to MAY?
>> 
>> IMO, this is a straightforward change that will provide more flexibility for implementations to process even non-conforming documents.
> I don't mind, but I can also live with SHOULD here.

Agreed, SHOULD is a bit stronger.

>>  One minor concern here is that this may now lead to non-standard extensions.
>> 
>> Consideration #2
>> ==============
>> Item #5 of Section 5.2 cautions against dynamically regenerating the schema from registry values at run-time; but also from downloading the base schema then too.
>> 
>> ---[ begin Item #5 of Section 5.2 ]---
>>    5.  There are security and performance implications in requiring
>>        implementations to dynamically download schemas at run time.
>>        Therefore, implementations SHOULD NOT download schemas at runtime
>>        unless the appropriate precautions are taken.  Implementations
>>        also need to contend with the potential of significant network
>>        and processing issues.
>> ---[ end Item #5 of Section 5.2 ]---
>> 
>> ** Do we want to strengthen the caution of not downloading the schema in real-time in Item #5 of Section 5.2 from SHOULD NOT to MUST NOT?
>> 
>> IMO, yes.
> Yes.

Yes

>> Consideration #3
>> ==============
>> 
>> As Robert suggests, minimally, there needs to be a discussion in the security considerations on how these new enum values will securely be added to the schema/parser.  However, the question remains, what guidance do we provide about how often the IANA registry should be checked.
>> 
>> ---[ begin Section 4.3]---
>>    Furthermore, the
>>    enumerated values present in this document are a static list that
>>    will be incomplete over time as select attributes can be extended by
>>    a corresponding IANA registry per Section 10.2.  Therefore, the
>>    schema to validate a given document MUST be dynamically generated
>>    from these registry values.
>> ---[ end Section 4.3 ]---
>> 
>> ** Should we modify the last sentence as follows:
>> 
>> "Therefore, the schema to validate a given document MUST be periodically regenerated from these registry values.  It is RECOMMENDED that this SHOULD NOT occur more frequently than xxx"
>> 
>> Kathleen/Alexey/or any reader of this note: do you have a pointer to the prior discussion on dynamically generating a schema from an IANA registry referenced by Robert so that "xxx" can be populated?
> I have no idea about reasonable "xxx" values. This was never done before. (When it was suggested before IESG persuaded authors to change their documents.)
> 
> While talking to www.iana.org directly from devices/programs is tempting, it might be better if vendors periodically download new values from IANA and then devices/programs talk to vendor's websites (or use vendor's update mechanisms).

I like Alexey's suggestion as it would greatly reduce the hits to IANA and accomplish the same goal.

Best regards,
Kathleen 

> 
> Best Regards,
> Alexey