Apple Safari WebKit HTMLFrameElementBase::isURLAllowed Subframe Overflow and Cross Origin Page Load

This strike exploits a vulnerability that exists inside Apple Safari Webkit. An attacker can insert frame elements with an empty URL into a node to overflow the subframe counter. When this node is later removed, the subframes won't be detached. The attacker can also make a subframe "survive" a cross-origin page load. It is possible for the new document to inherit the security context of its parent document, which can be an arbitrary cross-origin page, while the contents will be attacker-controlled.