September 13, 2011, 6:09 PM — The company also dealt with more fallout from the June hack of DigiNotar by flipping the "kill switch" on SSL (secure socket layer) certificates issued by Dutch certificate authority, or CA.
But none of the information Microsoft released today about the five updates or the 15 bugs was news: On Friday, the company leaked drafts of the security bulletins, the term Microsoft uses for the advisories that accompany each update.
All of the updates and vulnerabilities were rated "important," the second-most-serious rating in the company's four-step system.
Two of the vulnerabilities are in Windows; five are in Excel, the spreadsheet included with Office; two involve non-application Office components; and six affect SharePoint and associated software, such as Groove and Office Web Apps.
Of the 15, two are "DLL load hijacking" vulnerabilities, a term that describes a class of bugs first revealed in August 2010. Microsoft has been patching its software to fix the problem -- which can be exploited by tricking an application into loading a malicious file with the same name as a required dynamic link library, or DLL -- since last November.
Apparently that job isn't finished: Microsoft has yet to close a 2010 advisory that warns users of DLL load hijacking bugs in the company's software.
The update users should deploy first is MS11-072, which includes bug fixes for all supported versions of Excel, including the newest Excel 2010 on Windows and Excel 2011 on the Mac, several security professionals said today.
"The Excel one because of the attack vector, through malformed files," said Andrew Storms, director of security operations at nCircle Security, when asked which update should move to the top of the list.
Others experts agreed.
"Top priority should be given to MS11-072, which fixes an arbitrary code execution vulnerability in Excel," said Wolfgang Kandek, the chief technology officer for Qualys, in an email. "It affects all versions of Excel including the most recent 2010 version...[and] to exploit this issue, attackers could create malicious Excel files, which, when opened on vulnerable hosts, can take control of the system."
"Excel-related email attachments and links have commonly been used in attacks on organizations and this one should be addressed," added Kurt Baumgartner, senior security researcher at Kaspersky Lab.