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Re: MSIE (mshtml.dll) OBJECT tag vulnerability
From: Matthew Murphy <mattmurphy () kc rr com>
Date: Sat, 22 Apr 2006 20:13:54 -0500

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Michal Zalewski wrote:
Perhaps not surprisingly, there appears to be a vulnerability in how
Microsoft Internet Explorer handles (or fails to handle) certain
combinations of nested OBJECT tags. This was tested with MSIE
6.0.2900.2180.xpsp.040806-1825 and mshtml.dll 6.00.2900.2873
xpsp_sp2_gdr.060322-1613.

At first sight, this vulnerability may offer a remote compromise vector,
although not necessarily a reliable one. The error is convoluted and
difficult to debug in absence of sources; as such, I cannot offer a
definitive attack scenario, nor rule out that my initial diagnosis will be
proved wrong [*]. As such, panic, but only slightly.

On my XP SP2 box, your fourth example produces bizarre results.
FrontPage and Visual Studio survive it and appear to render it
semi-correctly.  Word renders it as plain text.  IE faults in mshtml.dll
with the null-pointer behavior you specified earlier.  However, *WINDOWS
EXPLORER* crashes in a very much exploitable way with what appears to be
a call through an uninitialized function pointer.

You end up with a function pointer being pulled from random places, so
sometimes it's exploitable and sometimes it isn't, but it seems like
this exploit interacts very differently with the shell than it does with
IE proper.  Exploiting that may be a bit hard, because (to my
knowledge), there's no way to remotely launch the shell itself.  I will
keep researching this, but there's obviously something exploitable going
on here...

As such, I think the "Panic, but only slightly" assessment is very
reasonable.

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