WkWebView looses cross-origin restriction (protection against malicious EPUBs)

[danielweck]

...because the file:// URI scheme / protocol cannot be used anymore for serving reader.html from the app-bundle (alongside HTTP://IP:PORT for serving the EPUB content documents). This also means that using different origins will bi-bidirectionally sandbox the iframe, preventing the Readium rendering engine (readium-shared-js) to perform some behaviour injection such as Media Overlays playback, annotations, etc.

See:
https://docs.google.com/document/d/1GK1aVsrTv23WroBWMX-XiwYtXbq6huW_pK8QXRaY6XQ/

Note that window.top / parent / frameElement.ownerDocument.defaultView cannot reliably be used to plug the security holes, so we removed them from the cloud reader and chrome extension.

[danielweck]

See:
https://github.com/readium/SDKLauncher-iOS/tree/feature/wkwebview
https://github.com/readium/readium-sdk/tree/feature/wkwebview