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Weighing in at about half the size of its giant October security patch, Microsoft's November security patch includes six security bulletins to address 15 vulnerabilities in Windows, Windows Server and Microsoft (NSDQ: MSFT) Office.

Three of the bulletins are designated "critical" and three are designated "important."

None of the bulletins affect Windows 7, which was officially released late last month, or Windows Server 2008 R2.

One of the critical vulnerabilities, addressed in MS09-065, is also rated 1 on Microsoft's Exploitability Index Rating, meaning that exploit code is likely.

MS09-065 describes a Windows kernel flaw could allow remote code execution on the machine of a victim who views a Web site or document with a specially crafted Embedded OpenType (EOT) font.

Microsoft is urging customers to make deployment of MS09-065 a priority and security researchers are saying the same thing.

"The EOT font parsing flaw can be used to execute code at the highest possible privilege level (the kernel) directly from Internet Explorer," said HD Moore, CSO at Rapid7 and chief architect of Metasploit, in an e-mailed statement. "Standard user-level defenses, like sandboxing, will have no effect on the exploitation of this flaw."

Ben Greenbaum, senior research manager at Symantec (NSDQ: SYMC) Security Response, concurs, noting that proof-of-concept exploit code is already available. "We think attackers will be paying a lot of attention to it in the future," he said.

Tyler Reguly, a senior security engineer with nCircle, notes that three of the vulnerabilities this month deal with listening services (MS09-063, MS09-064 and MS09-066) and represent a risk to enterprises more than home users.

MS09-067 and MS09-068 deal with file parsing bugs in Microsoft Office Excel and Word respectively, for Windows and for Mac (Office 2004 and 2008).