Re: [Simple] <note> in IMDN

[Paul Kyzivat <pkyzivat at cisco.com>]

Eric Burger wrote:
> 1. The content

Then aren't you concerned with all the nearly unconstrained content that 
is possible in sip itself? (quoted-strings can be used in many places, 
and comments are allowed in a few.)

In the context you are talking about, the content is constrained by the 
syntax of xml. Are you concerned with the xml parser screwing up? Or 
with an application screwing up processing the content after it has been 
parsed from the xml - perhaps by doing a bad job of trying to display it?

> 2. IMDN is only for page-mode IM, not MSRP

Oops, sorry. I forgot IMDN had been thrown out of MSRP.

	Paul

> On May 23, 2008, at 5:08 PM, Paul Kyzivat wrote:
> 
>> Eric,
>>
>> I guess I'm missing what kink of problem you are trying to prevent by
>> constraining the content, and what kinds of constraints are needed for
>> this to be helpful.
>>
>> Are you concerned with unconstrained *length* or unconstrained
>> *content*? You can already put fields of unconstrained length and nearly
>> unconstrained content into MSRP headers, in those places where
>> quoted-string are allowed.
>>
>>     Paul
>>
>> Eric Burger wrote:
>>> Actually, IMDNs, even the SIMPLE free-form fields, are fairly
>>> constrained.  Any mis-match is an opportunity to filter out bad IMDNs.
>>> The <note> field has three problems:
>>>
>>> 1. It cannot be filtered, as any content could be real (which introduces
>>> the attack vector)
>>>
>>> 2. It cannot know what language it should use, and thus is not likely to
>>> be useful to the recipient
>>>
>>> 3. It has no protocol value, and is of no value to the UA
>>>
>>>
>>> So, if something has no useful protocol value and introduces a spam
>>> opportunity, why would we want to include it?
>>>
>>>
>>>
>>> On May 21, 2008, at 7:45 PM, Paul Kyzivat wrote:
>>>
>>>> Its kind of late to be thinking about this now. THe problem is 
>>>> pervasive
>>>> in MSRP.
>>>>
>>>> In SIP there are lots of unconstrained fields. But they are all
>>>> constrained by the overall size of the message, and people commonly put
>>>> limits on that.
>>>>
>>>> In MSRP, because of chunking, a single MSRP message can be gigabytes
>>>> long. So using that to bound the unconstrained parts of the headers
>>>> doesn't work very well.
>>>>
>>>> A robust implementation might take a similar approach - define its own
>>>> limit on the total message size, excluding the body. Then it could
>>>> constrain all the unconstrained fields to fit within it.
>>>>
>>>> But picking on one header isn't a solution to the problem. Either 
>>>> assume
>>>> the developers will be able to deal with it, or else do and MSRPv2 that
>>>> eliminates all unconstrained fields.
>>>>
>>>>    Paul
>>>>
>>>> Dean Willis wrote:
>>>>> On May 13, 2008, at 11:38 PM, Hisham Khartabil wrote:
>>>>>
>>>>>> Can you explain how it is an attack vector?
>>>>>
>>>>>
>>>>> Unconstrained rich content is one of the most easily exploited attack
>>>>> vectors.
>>>>>
>>>>> Buffer overrun attacks as well as all of the typical MIME compound-
>>>>> component attacks are likely. For example, the common JPEG
>>>>> vulnerabilities might be exploitable:
>>>>>
>>>>> http://www.news.com/Image-virus-spreads-via-chat/2100-7349_3-5390463.html 
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Or the content-execution weakness that caused the Macintosh Safari
>>>>> browse to be most easily exploited in recent hacking contests:
>>>>>
>>>>> http://www.engadget.com/2007/07/23/safari-exploit-gives-hackers-full-control-of-your-iphone/ 
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> There have also been exploits against QuickTime, Flash, and most other
>>>>> plugin components from time to time.
>>>>>
>>>>> -- 
>>>>> Dean
>>>>> _______________________________________________
>>>>> Simple mailing list
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>>>>>
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>>>
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