On 11/1/16 6:36 AM, Roger Hågensen wrote:
Wait, are you saying that ContentSecurityPolicy can't be relied upon?


It depends on your threat model.

Content security policy is a tool that allows a web page to defend itself and its users from cross-site script injection attacks and the like. A fundamental assumption here is that the user is NOT the attacker, and hence the user's browser is cooperating with the web page to protect the user. It's a perfectly fine tool for the "user and page author are cooperating" threat model.

If, on the other hand, your threat model includes attacks by the _user_ on your server, you absolutely can't rely on CSP to defend against that. Most simply, the user can use a browser that doesn't support CSP. For addressing this class of attacks, you _have_ to rely on a completely server-side solution, because by assumption the client (the browser) is the attacker in this situation.

-Boris

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