Javascript and plugging holes was: [xml-dev] Cross-domain loading of XML

[Stephen Green <stephengreenubl@gmail.com>]

>
> It's an accident of history that scripts, plug-in content and images from a different origin are allowed by default. If it were possible to plug this hole without Breaking the Web, it would probably have been plugged already.
>

Isn't it true that much of what is done these days with Javascript
these days (jQuery, etc) is
powerful because it exploits holes which haven't (yet!) been plugged?
Isn't that one factor
which gives JSON an edge on XML? Maybe JSON and jQuery and the like
are best kept to
short-term goals but XML more likely to be used for longterm goals
(like documents/archives)
since there is the risk that the security concerns will eventually
overrule the worry about
Breaking the Web and holes will be plugged which break much of what is
done today with
Javascript/jQuery (even HTML5?) and JSON? (I hope I'm not spreading
mere FUD by saying this).

----
Stephen D Green



On 9 December 2010 15:17, Henri Sivonen <hsivonen@iki.fi> wrote:
> On Dec 8, 2010, at 16:21, Mike Sokolov wrote:
>
>> However there is a workaround for JSON (they call it JSONP) that uses the ability to load javascript dynamically from another domain.  Essentially, it seems you can bypass the cross-domain restriction by this trick:
>>
>> var script = document.createElement('script');
>> script.setAttribute('src', url);
>>
>> Apparently in this instance url doesn't have to be a url on the same domain.
>
> This has two problems. I noticed only one of them mentioned in the article.
>
> If you are the site using someone else's JSON-P data source, that someone else gets to execute code with the privileges of your origin. They might be serving you code that calls the callback you want with the JSON data you want today, but tomorrow they might serve you something else that gets run in your origin. Thus, if you use someone else's JSON-P service, you have to trust them enough to give them the technical opportunity to do with your users' data anything that your own front end code could do.
>
> The second problem relates to private data. That is, data that you wouldn't serve without login credentials. The Same-Origin Policy is there to protect private data. If you use JSON-P to bypass the Same-Origin Policy, you don't get the protection. Thus, if you serve private data as JSON-P when the request is authorized by HTTP authentication or by a cookie, if the user visits a rogue site while being logged into your site, the rogue site can access the private data offered by you as JSON-P by including the JSON-P file as a script to the rogue site.
>
> It's an accident of history that scripts, plug-in content and images from a different origin are allowed by default. If it were possible to plug this hole without Breaking the Web, it would probably have been plugged already.
>
>> I don't see why this couldn't be used to insert any sort of data at all, but it does rely on javascript.
>
> Indeed, if you could transfer an XML document
> <bar/>
> as a file that says
> foo("<bar/>");
> and call it XML-P. It would have the same in-security properties as JSON-P.
>
> --
> Henri Sivonen
> hsivonen@iki.fi
> http://hsivonen.iki.fi/
>
>
>