During their already busy Patch Day, Microsoft snuck out a security advisory warning their customers that attackers are exploiting a previously undiscovered vulnerability in XML Core Services to launch drive-by download attacks in the wild.
Microsoft’s XML Core Services (MSXML) is basically a component that helps Windows, Internet Explorer, and other Microsoft products to handle XML content. XML Core Services ships with various versions of Windows, and many other Microsoft products. If you have a Windows computer, you probably have XML Core Services installed.
According to the security advisory, XML Core Services suffers from an unpatched memory corruption vulnerability, which attackers can exploit to execute code on your machine. The attacker only has to lure you to a web site containing maliciously crafted code for his attack to succeed.
Since Microsoft first learned of this vulnerability through actual attacks in the wild, they haven’t had time to create and release a full patch yet. However, they have released what they call a “Fixit“, which is supposed to block this particular attack vector. If you manage a Microsoft network, I recommend you apply this Fixit on your Windows machines.