[webkit-gtk] Client side security policy?

Michael A. Peters mpeters at mac.com
Thu Mar 18 15:53:10 PDT 2010

David P. Reed wrote:
> To be honest, I hate the idea that one should disable large parts of 
> emerging standard capability such as Javascript, CSS, fonts, ...  this 
> just makes web designers have to deal with users demanding all forms of 
> crippling be supported.

CSP only disables what the web master states (via a header) is not used 
and therefore suspicious if it is in the page.

The point is to provide clients with protection against XSS.

For example, the policy header I send states that JavaScript, audio, 
video, object, and CSS on my web site only originate from my web site. 
So if I have an input validation error or other hole in the software I 
run that allows John Q. Malware to insert his own JavaScript into my 
page, FireFox (development versions anyway) will see that the JavaScript 
comes from a source not listed by my CSP policy and block it.

Furthermore, browsers can report the blockage via post to a specified 
URL on my server so that I (the web master) will know there was a policy 
violation and can either correct the situation (by allowing the resource 
in my CSP or by taking care of the injected XSS).

Web masters that do not send a header don't get anything blocked 
regardless of origin. No CSP policy sent in a header means no resources 
blocked. So CSP does not disable any emerging standard capabilities.

If CSP is implemented in web kit browsers, that should of course be the 
default unless the user specifically wants to tighten down their browser 
by setting their own policy of what they allow and from where, which is 
functionality provided in FireFox for some time via NoScript, only doing 
it as a default CSP policy would allow even better control.

For example, I could set a policy white lising img csss from anywhere 
and JavaScript, video audio object embed elements that originate from 
the same server of the page (policy of self) and only block those from 
other domains that I haven't white-listed.

These new technologies are nice but at the same time give vectors of 
attacking users and doing things with the users browser that the user 
does not want done and things that are down right malicious.

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