An unpatched Windows vulnerability considered a critical threat by security experts is being exploited by cybercriminals.
Microsoft disclosed the flaw in XML Core Services (MSXML) 3.0, 4.0 and 6.0 June 12 during its monthly release of patches. The security advisory, which was separate from the patch release, offered a workaround for vulnerability CVE-2012-1889, but no fix.
Vulnerability CVE-2012-1889 is simple to exploit in all known versions of Internet Explorer. An attacker can make a CLSID-identification request by calling MSXML library methods and create an object identifier in order to try to access a non-existent object. Proof of Concept code for causing a crash looks like this:
This code looks simple, but generates memory corruption and crashes Internet Explorer. The exploitation code tries to request a non-initialized object, but reference to memory region already exists. Memory corruption takes place in the helper function _dispatchImpl :: InvokeHelper() in the MSXML library.
Currently, this vulnerability has no patch available but Microsoft has released a Fix it solution. We strongly suggest that you consider this workaround – for now.