Re: [Simple] <note> in IMDN

[Paul Kyzivat <pkyzivat at cisco.com>]

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
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> 
> 
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