CVE-2014-1785: MSIE 11 MSHTML CSpliceTreeEngine::RemoveSplice use-after-free

Since November I have been releasing details on all vulnerabilities I
found that I have not released before. This is the 36th entry in the
series. This information is available in more detail on my blog at
http://blog.skylined.nl/20161220001.html. There you can find a repro
that triggered this issue in addition to the information below, as well
as a Proof-of-Concept exploit that attempts to prove exploitability.

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MSIE 11 MSHTML CSpliceTreeEngine::
RemoveSplice use-after-free
=============================================================
(MS14-035, CVE-2014-1785)

Synopsis
--------
A specially crafted web-page can trigger a use-after-free vulnerability
in Microsoft Internet Explorer 11. There is sufficient time between the
free and reuse for an attacker to control the contents of the freed
memory and exploit the vulnerability.

Known affected software, attack vectors and potential mitigations
-----------------------------------------------------------------
* Microsoft Internet Explorer 11

  An attacker would need to get a target user to open a specially
  crafted web-page. Disabling JavaScript should prevent an attacker
  from triggering the vulnerable code path.

Details
-------
This was one of the first bugs where I attempted to do a proper
analysis, and I got some feedback from ZDI that explained what I got
right and what I got wrong. Basically, on x86, a 0x28 byte memory block
is allocated in `MSHTML!CMarkup::DoEmbedPointers` and when you execute
`document.execCommand("Delete")`. This memory can be freed when you
execute `document.open()` in a `DOMNodeRemoved` event handler. After
that, you can use Javascript to reallocate the memory before it is reused.

Time-line
---------
* 30 December 2013: This vulnerability was submitted to ZDI.
* 8 January 2014: This vulnerability was acquired by ZDI.
* 14 January 2014: This vulnerability was disclosed to Microsoft by ZDI.
* 10 June 2014: This vulnerability was address by Microsoft in MS14-035.
* 20 December 2016: Details of this vulnerability are released.

Cheers,

SkyLined