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Revision as of 21:43, 7 August 2007 by Paulproteus (talk | contribs) (Client interaction: complete.js query string)
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This page lists security considerations for the JsWidget. By exposing the design's use of input and the way it generates output and soliciting feedback on this, we hope to avoid correctness errors that can lead to vulnerabilities in our servers or the web applications of those who use our JsWidget.

Warning: This might be boring.


The JsWidget only creates DOM objects and CSS styles that begin with cc_js_, so they cannot overwrite your objects or styles unless you use the cc_js_ "namespace".

Input validation


complete.js is implemented as a PHP file. It reads in the prerequisite JavaScript files from the filesystem, never the network, and sends them to the user.

It also sends a reference to the desired localized template. This is based on the $_SERVER['SCRIPT_PATH'] and $_SERVER['HTTP_HOST'] header. The SCRIPT_PATH header is created by PHP and cannot be forged as far as I know. HTTP_HOST is taken from the user's Host: header, which in a normal HTTP/1.1 user agent is the domain of the web site the user is requesting the file from (in our case, it should always be api.creativecommons.org).

Spoofing the HTTP Host: header would cause Apache to dispatch to a different virtual host, so in effect it must be correct.

Output generation

The complete.js file adds a <script> tag to the document it is included into, which causes the browser to request a static file, template.js (perhaps localized). This file document.write()s HTML to the page, but the validity of that HTML as XML has already been checked by the Python program that generated template.js.

The cc-jurisdictions.js file is generated nightly by Python. Only one section of the file is updated, and it is validated to be a single JSON object so the process by which the file is generated precludes it from modifying more than one variable. The variable it does modify is decoded from JSON and validated for equality to the Python object that generated it before the file is modified. That way, any invalid input during the generation of the jurisdiction array is caught before they are saved into a file that is served to web clients.

Client interaction and network activity

All JsWidget DOM calls start with references to the cc_js_$() function, which ensures that it only modifies DOM elements prefixed by cc_js_. By verifying this, you can see that we do not have access to user data other than the forms created by us.

The JsWidget JS files do no network activity once they have been downloaded to the client. By verifying this, you can see that we do not send any information (personally identifiable or otherwise) any CC.org servers except as part of downloading the widget.

complete.js takes an input variable of ?locale= in the query string. It matches this against the regex /^([a-zA-Z-_]+)$/ to ensure only alphanumeric characters and hyphens and underscores are part of the value (as well as that the value is not empty), and if that is true, it asks the client to requests a file with these characters suffixed onto a URL. The chosen characters do not need to be escaped, so no escaping is done.