Internet Explorer incorrectly under-allocates memory to store a certain combination of Cascading Style Sheets (CSS) tags when parsing HTML. This could result in an overwrite of the least significant byte of a vtable pointer. An attacker able to spray memory with a specific pattern could potentially execute code in the context of the process parsing the HTML. The defense against heap spray style attacks is Data Execution Prevention (DEP).
DEP is enabled by default in Internet Explorer 8, and users should consider enabling it in earlier versions.
Users of Internet Explorer might want to do so quickly, as security researcher Roger Thompson noted in his blog that attack software for this vulnerability has been incorporated in the Eleonore Exploit Kit saying that "This raises the stakes considerably, as it means that anyone can buy the kit for a few hundred bucks, and they have a working 0-day."
Microsoft is due to release its scheduled monthly batch of security patches tomorrow, but don't expect this Internet Explorer flaw to be one of them. Microsoft has said it will release a critical flaw in multiple versions of its Microsoft Office suite as well as a fix for its Forefront Unified Access Gateway.
The good news here is that this month administrators won't have to contend with anything near the whopping 49 vulnerabilities last month.
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