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Re: ACTION-893: Start putting together a set of guidelines that could help address the security issues triggered by links rewriting.

From: David Storey <dstorey@opera.com>
Date: Sun, 18 Jan 2009 15:44:28 +0100
Message-Id: <EE451168-ABF4-4E40-B992-6A1AD9A11DD3@opera.com>
To: Mobile Web Best Practices Working Group WG <public-bpwg@w3.org>

On 17 Jan 2009, at 12:19, Tom Hume wrote:

> Rob
> Your points re operational procedures are true... but don't they  
> nevertheless introduce risk to content providers wishing to ensure  
> security? If I set up a secure service that isn't transcoded, I know  
> that communications between client and server are secure. If it's  
> transcoded (which it may be by a large number of operators  
> worldwide) I'm suddenly dependent on the operational procedures and  
> integrity of all these operators. I'd be surprised if I, as a  
> content provider, was able to evaluate these.

This is not strictly true, in that you still have to trust the  
client.  One could say you can't trust Opera Mini as it doesn't have  
end to end SSL, but on a regular browser the SSL is obviously  
decrypted on the client.  That client (say Opera desktop) could just  
as easy do something malicious with the private data if the vendor  
wasn't trustworthy.  I guess there would be an additional step in  
phoning home to return the data to the mother ship though.

In short I think you have to trust the proxy vendor as much as you  
trust the client vendor.  I guess one difference is that certain  
proxies the end user chooses to use, such as by downloading and using  
Opera Mini, but it is a different ball game for proxies that operators  
push on the user without them selecting it (i.e. given to all mobile  
browsers).  I think the former is fine but not so much the latter.

In regard to the no transform header; this can't work for solutions  
such as Opera Mini, where they only support using a proxy.

> A similar point exists re software audit; are we expecting or  
> mandating transcoder deployments to have gone through such an audit,  
> and publish its details publicly? Unless such an audit is visible  
> it's probably of little comfort.
> (5) seems to be getting into the business of specifying the internal  
> operations of transcoders, something we've so far shied away from  
> doing (though I can see that this issue may be serious enough to  
> start justifying this).
> (6) seems similar, and (rightly) introduces a load of new  
> responsibilities for transcoder deployments. If we're to use this as  
> the basis for meaningful, testable guidelines (as the rest of the CT  
> doc) then we'll need to get very specific on the details of what  
> managing browser sessions entails - particularly given the fact that  
> some sites deliberately share cookies, whilst others mustn't. For  
> instance, as fred.futureplatforms.com I might set a cookie  
> for .futureplatforms.com and expect ginger.futureplatforms.com to  
> use it. So it's not enough to present only cookies originally set by  
> the origin server - there's some more logic needed in the proxy for  
> this. Equally cookies presented between client and proxy shouldn't  
> go any further, I suspect...
> Are there other assumptions that web applications typically make  
> around the name of the origin server, I wonder?
> There are other issues here (which I think have been raised before  
> by Luca) around non-repudiation - that CPs may have sound reasons to  
> rely on users not being able to claim "I didn't do it" later on (on,  
> say, auction sites) and any rewriting of links introduces doubt here.
> I'd also venture that if this discussion is around transcoding of  
> existing web services, and particularly long-tail web services, then  
> any solution which implies providers of web services have to do some  
> work (e.g. by detecting Via headers and responding with 406 codes,  
> which I think has been suggested previously) isn't appropriate IMHO.
> Tom
> On 16 Jan 2009, at 20:20, Robert Finean wrote:
>> http://www.w3.org/2005/MWI/BPWG/Group/track/actions/893
>> This is a first draft, all comments welcome:
>> ----
>> When a CT-Proxy is a "man-in-the-middle" a high level of trust  
>> needs to
>> be established with the mobile network operator and end-user before a
>> user chooses to allow transformation of their private data. Their
>> concerns are:
>> 1. A 3rd-party could see their secure details, even by accident.
>> 2. Malicious software could snoop secure details or copy them.
>> 3. Secure details could be recovered from a discarded faulty hard- 
>> disk.
>> 4. A system administrator could see secure details by logging into  
>> the
>> CT-Proxy server, even by accident.
>> 5. Secure details could be logged by the CT-Proxy's operator for
>> business analysis.
>> 6. Their secure details may in fact be going to a fraudulent website,
>> not the website they expected (a phishing scam).
>> 7. Their logged-in session with a website could be hijacked by  
>> someone
>> spoofing their identity.
>> 1 is addressed using encryption on all connections to/from the CT- 
>> proxy
>> and by ensuring that any caching at the CT-proxy complies with  
>> RFC2616
>> and RFC2109 with respect to public/private caching rules.
>> 2 is addressed through software audit.
>> 3 & 4 are addressed by operations procedures and by encrypting all  
>> user
>> data on disks.
>> 5 is addressed by never logging anything more than origin domain name
>> for HTTPS transactions (ie only log what HTTP CONNECT would reveal).
>> 6 is complicated by the fact that often a CT-Proxy has to operate  
>> as a
>> gateway, when it ceases to be a "proxy" and becomes an "end point".
>> For instance:
>> * When a long web-page gets fragmented, links to subsequent fragments
>> must target the CT-proxy as the origin server.
>> * JavaScript events triggered by links in the device's static XHTML/ 
>> MP
>> markup must target the CT-proxy as the script execution environment.
>> * HTTPS links must be rewritten to transcode an HTTPS web site.
>> * To minimize the size of the page returned to the end user, long  
>> URIs
>> may be replaced by short "tokens" that only the issuing CT-proxy can
>> redeem.
>> At the URI level, this means that the URI moves from:
>> http://[original-URI]
>> ... to something like:
>> http://ct-proxy.example.com/[original-URI]
>> This change of origin hostname is important because of the security
>> implications it has on the browser for cookies (which belong to
>> hostnames) and for script Document Object Model security (if the  
>> device
>> has any script capabilities then cross-site scripting attacks become
>> possible). From the device browser's perspective the CT-proxy makes  
>> the
>> Web look as if it is all from one origin.
>> The solution to this is for the CT-proxy to manage all cookies and  
>> all
>> script execution on behalf of the device whenever the CT-Proxy is the
>> URI end-point. The CT-proxy should not pass origin-server scripts
>> through to the device for execution or pass origin-server cookies  
>> to the
>> device. The CT-proxy must manage its script execution security and
>> cookie/hostname security in the same way as a web browser to prevent
>> malicious cross-site scripting exploits. [RFC2109] [reference on DOM
>> security?]
>> The CT-proxy must manage the browsing session (including the change  
>> of
>> referer, the use of client certificates, etc) on behalf of the end- 
>> user.
>> 7 is only a threat when the CT-proxy is managing the browsing  
>> session on
>> behalf of the user's device browser. In this case the CT-proxy  
>> needs to
>> uniquely identify requests from each user, with either out-of-band
>> authentication using the radio network's SIM identity or by using
>> cookies between the user's browser and the CT-proxy. [Reference on
>> secure session management using cookies?]
> --
> Future Platforms Ltd
> e: Tom.Hume@futureplatforms.com
> t: +44 (0) 1273 819038
> m: +44 (0) 7971 781422
> company: www.futureplatforms.com
> personal: tomhume.org

David Storey

Chief Web Opener,
Product Manager Opera Dragonfly,
Consumer Product Manager Opera Core,
W3C Mobile Web Best Practices Working Group member

Consumer Product Management & Developer Relations
Opera Software ASA
Oslo, Norway

Mobile: +47 94 22 02 32
E-Mail: dstorey@opera.com
Blog: http://my.opera.com/dstorey
Received on Sunday, 18 January 2009 14:45:15 UTC

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