MSIE8 MSHTML Ptls5::Ls­Find­Span­Visual­Boundaries memory corruption

[Berend-Jan Wever <berendj () nwever nl>]

Throughout November, I plan to release details on vulnerabilities I
found in web-browsers which I've not released before. This is the
fifteenth entry in that series. Unfortunately I won't be able to
publish everything within one month at the current rate, so I may
continue to publish these through December and January.

The below information is available in more detail on my blog at
http://blog.skylined.nl/20161121001.html.

Follow me on http://twitter.com/berendjanwever for daily browser bugs.

MSIE8 MSHTML Ptls5::LsFindSpanVisualBoundaries memory corruption
================================================================
(The fix and CVE number for this bug are unknown)

Synopsis
--------
A specially crafted web-page can cause an unknown type of memory
corruption in Microsoft Internet Explorer 8. This vulnerability can
cause the `Ptls5::LsFindSpanVisualBoundaries` method (or other methods
called by it) to access arbitrary memory.

Known affected software, attack vectors and mitigations
-------------------------------------------------------
* Microsoft Internet Explorer 8

  An attacker would need to get a target user to open a specially
  crafted web-page. JavaScript is not necessarily required to trigger
  the issue.

Description
-----------
The memory corruption causes the `Ptls5::LsFindSpanVisualBoundaries`
method to access data at seemingly random addresses. However, these
addresses appear to always be in the same range as valid heap addresses,
even if they are often not DWORD aligned. The reason for the memory
corruption is not immediately obvious.

Time-line
---------
* July 2014: This vulnerability was found through fuzzing.
* November 2016: Details of this issue are released.

Cheers,

SkyLined

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