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Re: MSIE (mshtml.dll) OBJECT tag vulnerability
From: <ipatches () hushmail com>
Date: Mon, 24 Apr 2006 16:18:08 -0500

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.

Probably the easiest way to trigger the problem is as follows:

  perl -e '{print "<STYLE></STYLE>\n<OBJECT>\nBork\n"x32}' 
test.html

...this will (usually) cause a NULL pointer + fixed offset 
(eax+0x28)
dereference in mshtml.dll, the pointer being read from allocated 
but still
zeroed memory region.

The aforementioned condition is not exploitable, but padding the 
page with
preceeding OBJECT tag (and other tags), increasing the number of 
nested
OBJECTs, and most importantly, adding bogus 'type=' parameters of 
various
length to the final sequence of OBJECTs, will cause that 
dereference to
become non-NULL on many installations; then, a range of other 
interesting
faults should ensue, including dereferences of variable bogus 
addresses
close to stack, or crashes later on, when the page is reloaded or 
closed.

[ In absence of sources, I do not understand the precise 
underlying
  mechanics of the bug, and I am not inclined to spend hours with 
a
  debugger to find out. I'm simply judging by the symptoms, but 
these
  seem to be indicative of an exploitable flaw. ]

Several examples of pages that cause distinct faults in my setup 
(your
mileage may and probably WILL vary; on three test machines, this 
worked as
described; on one, all examples behaved in non-exploitable 0x28 
way):

  http://lcamtuf.coredump.cx/iedie2-1.html (eax=0x0, instant 
dereference)
  http://lcamtuf.coredump.cx/iedie2-2.html (bogus esi on 
reload/leave)
  http://lcamtuf.coredump.cx/iedie2-3.html (page fault on browser 
close)
  http://lcamtuf.coredump.cx/iedie2-4.html (bogus esi on 
reload/leave)

Well, that's it. Feel free to research this further. This 
vulnerability,
as requested by customers, is released in strict observance of 
the Patch
Wednesday & Bug Saturday policy.

[*] The ability of the attacker to document the attack scenario 
probably
    doesn't matter for those who pretend to care; cryptic "hi" to
    Secunia and their standards of conduct.
Sir, You work very well! I think you must also pester Microsoft. I 
also remember LSD pesters Microsoft and they were rapidly sold out.



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