MSIE 9 MSHTML CElement::Has­Flag memory corruption

Since November I have been releasing details on all vulnerabilities I
found that I have not released before. This is the twenty-ninth entry
in the series. This information is available in more detail on my blog
at http://blog.skylined.nl/20161209001.html. There you can find a repro
that triggered this issue in addition to the information below.

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MSIE 9 MSHTML CElement::HasFlag memory corruption
==============================
===================
(The fix and CVE number for this issue are not known)

Synopsis
--------
A specially crafted web-page can trigger a memory corruption
vulnerability in Microsoft Internet Explorer 9. I did not investigate
this vulnerability thoroughly, so I cannot speculate on the potential
impact or exploitability.

Known affected software and attack vectors
------------------------------------------
* Microsoft Internet Explorer 9

  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 bug was found back when I had very little knowledge and tools to do
analysis on use-after-free bugs, so I have no details to share. In
addition, EIP said they were already aware of the bug and provided no
details, this issue appears to have been fixed before ZDI was able to
look at it.

Time-line
---------
* 27 September 2012: This vulnerability was found through fuzzing.
* 7 November 2012: This vulnerability was submitted to EIP.
* 27 November 2012: This vulnerability was rejected by EIP.
* 28 November 2012: This vulnerability was submitted to ZDI.
* Between December 2012 and February 2013: Microsoft addresses this
  vulnerability.
* 27 February 2012: This vulnerability was rejected by ZDI.
* 8 December 2016: Details of this vulnerability are released.

I would like to note that although ZDI did not acquire the vulnerability
as it was patched before they could finish analysis, they did offer me
ZDI reward points as a courtesy.

Cheers,

SkyLined