This module exploits a use-after-free vulnerability found in Internet Explorer,
specifically in how the browser handles the caret (text cursor) object. In IE's
standards mode, the caret handling's vulnerable state can be triggered by first
setting up an editable page with an input field, and then we can force the caret
to update in an onbeforeeditfocus event by setting the body's innerHTML property.
In this event handler, mshtml!CCaret::`vftable' can be freed using a document.write()
function, however, mshtml!CCaret::UpdateScreenCaret remains unaware aware of this
change, and still uses the same reference to the CCaret object. When the function
tries to use this invalid reference to call a virtual function at offset 0x2c, it
finally results a crash. Precise control of the freed object allows arbitrary code
execution under the context of the user.
The vuln works against IE8 on Win 7, but the current version of the custom spray
doesn't actually work well against that target. More work is needed before we can
add that target for sure. The reason a custom spray is needed is because the
document.write() function erases the typical spray routines we use like
js_property_spray, or the heaplib + substring one. Tried using an iframe too,
but onbeforeeditfocus event doesn't seem to work well in an iframe (does not
fire when innerHTML is used.)
Tod Beardsley
jvazquez-r7
sinn3r