The vulnerability in the Server Message Block (SMB) 2 network file- and print-sharing protocol that ships with those versions of the Windows operating system was first disclosed late last Monday, when a researcher posted exploit code.
The next day, Microsoft issued a security advisory confirming the bug and the fact that it could be used to "take complete control of an affected system."
Microsoft did note that the release to manufacturing, or RTM, editions of Windows 7 and Windows Server 2008 R2 are not affected, along with earlier versions of the operating system, including Windows 2000, XP and Server 2003.
However, the vulnerable release candidates have been widely distributed, with millions of users downloading Windows 7 RC when it was publicly available from early May through mid-August.
Microsoft recommended that users either disable SMB 2 by editing the Windows Registry -- a task too daunting for most consumers -- or block TCP Ports 139 and 445 at the firewall until a patch is available. However, the company acknowledged that blocking those ports would cripple several services and applications.
As expected, a patch for the recently revealed vulnerability in its Internet Information Services Web server wasn't ready in time for the monthly update.