When an `iframe` has a `sandbox` attribute and its content is specified using `srcdoc`, that content does not inherit the containing page’s Content Security Policy (CSP) as it should unless the sandbox attribute included `allow-same-origin`. External Reference: https://www.mozilla.org/en-US/security/advisories/mfsa2017-18/#CVE-2017-7788 Acknowledgements: Name: the Mozilla project Upstream: Muneaki Nishimura