Re: [Slim] Alissa Cooper's No Objection on draft-ietf-slim-negotiating-human-language-22: (with COMMENT)

Paul Kyzivat <pkyzivat@alum.mit.edu> Thu, 11 January 2018 20:53 UTC

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To: Randall Gellens <rg+ietf@randy.pensive.org>, slim@ietf.org
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From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Thu, 11 Jan 2018 15:52:57 -0500
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Subject: Re: [Slim] Alissa Cooper's No Objection on draft-ietf-slim-negotiating-human-language-22: (with COMMENT)
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On 1/10/18 11:27 AM, Randall Gellens wrote:
> At 11:01 AM -0500 1/10/18, Paul Kyzivat wrote:
> 
>>  On 1/9/18 3:08 PM, Randall Gellens wrote:
>>>  Hi Alissa,
>>>
>>>  Good point.  I can reword the Security Considerations section to read:
>>>
>>>      The Security Considerations of BCP 47 [RFC5646] apply here.  An
>>>      attacker with the ability to modify signaling could prevent a call
>>>      from succeeding by altering any of several crucial elements,
>>>      including the 'hlang-send' or 'hlang-recv' values.  RFC 5069
>>>      [RFC5069] discusses such threats.  Use of TLS or IPSec can protect
>>>      against such threats.  Emergency calls are of particular 
>>> concern; RFC
>>>      6881 [RFC6881], which is specific to emergency calls, mandates 
>>> use of
>>>      TLS or IPSec (in ED-57/SP-30).
>>
>>  Is this a real concern? IIUC the processing of emergency calls 
>> prioritizes completion of the call above everything else. Lack of 
>> support for a requested language should never result in call failure.
> 
> It's a concern for calls in general that an attacker who is able to 
> modify the signaling can cause calls to fail.  The attacker could modify 
> the Request-URI, causing the call to be routed to, e.g., a pothole 
> reporting line instead of the police, or to a completely bogus 
> destination, or modify the Contact-URI or any other crucial element.  

But that is nothing unique to SLIM. In this respect it is the same as 
any sip call.

	Thanks,
	Paul

> It's true that where emergency calls are concerned, normally the 
> priority is for the call to complete no matter what.  A PSAP is highly 
> unlikely to fail a call if there are no languages in common.  RFC 6881 
> mandates use of TLS or IPSec but also that a call proceeds even if TLS 
> or IPSec fail.
> 
> 
>>>  At 10:18 AM -0800 1/9/18, Alissa Cooper wrote:
>>>
>>>>   Alissa Cooper has entered the following ballot position for
>>>>   draft-ietf-slim-negotiating-human-language-22: No Objection
>>>>
>>>>   When responding, please keep the subject line intact and reply to all
>>>>   email addresses included in the To and CC lines. (Feel free to cut 
>>>> this
>>>>   introductory paragraph, however.)
>>>>
>>>>
>>>>   Please refer to 
>>>> https://www.ietf.org/iesg/statement/discuss-criteria.html
>>>>   for more information about IESG DISCUSS and COMMENT positions.
>>>>
>>>>
>>>>   The document, along with other ballot positions, can be found here:
>>>>
>>>> https://datatracker.ietf.org/doc/draft-ietf-slim-negotiating-human-language/ 
>>>>
>>>>
>>>>
>>>>
>>>>   
>>>> ----------------------------------------------------------------------
>>>>   COMMENT:
>>>>   
>>>> ----------------------------------------------------------------------
>>>>
>>>>   == Section 7 ==
>>>>
>>>>   "In
>>>>      addition, if the 'hlang-send' or 'hlang-recv' values are 
>>>> altered or
>>>>      deleted en route, the session could fail or languages
>>>>      incomprehensible to the caller could be selected; however, this is
>>>>      also a risk if any SDP parameters are modified en route."
>>>>
>>>>   Given that one of the primary use cases for the attributes defined 
>>>> here is for
>>>>   emergency calling, it seems worthwhile to call out the new 
>>>> specific threat that
>>>>   these attributes enable in that case, namely the targeted 
>>>> manipulation/forgery
>>>>   of the language attributes for the purposes of denying emergency 
>>>> services to a
>>>>   caller. This general class of attacks is contemplated in Section 
>>>> 5.2.2 of RFC
>>>>   5069, although there may be a better reference to cite here for 
>>>> what to do if
>>>>   you don't want your emergency calls subject to that kind of attack 
>>>> (I can't
>>>>   recall another document off the top of my head).
>>>>
>>>>   == Section 8 ==
>>>>
>>>>   This seems weak for not including some words to indicate what to 
>>>> do to mitigate
>>>>   the risks of exposing this information.
>>>
>>>
>>
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> 
>