XSS, one of the most common web vulnerabilities, can be completely prevented with a strict Content Security Policy (CSP). Older versions of CSP involved the tedious process of building a whitelist of domains where scripts lived. It is very common for these whitelists to contain sites that allow for arbitrary code execution and developers cannot use inline scripts without disabling the XSS protections. Version 3 of CSP introduced a mechanism called strict-dynamic that makes applying content security policy to an existing web page possible without having to do major refactors. This talk will cover how we applied a strict CSP to pinterest.com and instapaper.com including how easy it is and some things to watch out for. I'll also cover what kinds of attacks are still possible after a strict CSP is deployed.
