In IE8 standards mode, it's possible to cause a use-after-free condition by first
creating an illogical table tree, where a CPhraseElement comes after CTableRow,
with the final node being a sub table element. When the CPhraseElement's outer
content is reset by using either outerText or outerHTML through an event handler,
this triggers a free of its child element (in this case, a CAnchorElement, but
some other objects apply too), but a reference is still kept in function
SRunPointer::SpanQualifier. This function will then pass on the invalid reference
to the next functions, eventually used in mshtml!CElement::Doc when it's trying to
make a call to the object's SecurityContext virtual function at offset +0x70, which
results a crash. An attacker can take advantage of this by first creating an
CAnchorElement object, let it free, and then replace the freed memory with another
fake object. Successfully doing so may allow arbitrary code execution under the
context of the user.
This bug is specific to Internet Explorer 8 only. It was originally discovered by
Orange Tsai at Hitcon 2013, but was silently patched in the July 2013 update, so
no CVE as of now.
Tod Beardsley
sinn3r