(The fix and CVE number for this issue are not known)
A specially crafted web-page can trigger a use-after-free vulnerability in
Microsoft Internet Explorer 9. During a method call, the
this object can be
freed and then continues to be used by the code that implements the method.
It appears that there is little to no time for an attacker to attempt to
control the contents of the freed memory before the re-use, which would allow
remote code execution.
Microsoft Internet Explorer 9
<script defer> document.designMode = "on"; </script> <q dir="ltr"> <ruby dir="rtl">
By switching the a document's
designMode property to
on in a deferred
script, MSIE 9 can be made to reload a web page using
CMarkup::. This method calls
which indirectly calls
CScriptCollection::~CScriptCollection, which releases
CMarkup object used as
The relevant stack for the freeing of this
CMarkup object is:
76e8c484 kernel32!HeapFree+0x00000014 6780c4d8 MSHTML!CMarkup::`vector deleting destructor'+0x00000026 6776fb9b MSHTML!CScriptCollection::~CScriptCollection+0x00000152 67816a0d MSHTML!CScriptCollection::
Release+0x00000053 6751f7e7 MSHTML!CWindow:: SuperNavigateInternal+0x000004c4 675209f7 MSHTML!CWindow:: SuperNavigate2WithBindFlags+0x00000032 679b05f8 MSHTML!CDoc:: CompatViewRefresh+0x000000a0 679c00d4 MSHTML!CMarkup:: ReloadInCompatView+0x0000021f
Immediately after returning to
CMarkup::, the code will use
the (now freed)
CMarkup object. When page heap is enabled, this lead to an
immediate access violation.
I did not immediately find a way to control the freed memory before the reuse
CDoc:: call. I did not immediately find other
locations in the code where the same stale pointer to the
CMarkup object is
used after it has been freed. It may not be possible to exploit this
use-after-free, as there does not appear to be an easy window of opportunity to
modify the freed memory before its reuse.
However, when loading the repro in MSIE with page heap disabled, I do see crashes from time to time, but in different locations in the code. This indicates that one or more of the following should be true:
CMarkupobject before it is reused.
CMarkupobject is used after it has been freed, and the freed
CMarkupobject can be modified before this happens.
As these other crash stacks do not include
seems most likely that they are caused by the second or third option, which
could indicate that the bug is in fact exploitable.
dll!CMarkup:: ReloadInCompatView Arbitrary~E58 AVR(D6B0C524) description: Security: Attempt to read from unallocated arbitrary memory (@0x22E22E58) in MSHTML. dll!CMarkup:: ReloadInCompatView note: The exception happens in the main process. Based on this information, this is expected to be a critical security issue!