Microsoft Fixes Excel, Office Flaws During September Patch Tuesday Update

Microsoft's September Patch Tuesday release had no "critical" patches for the first time in a long time.

Microsoft fixed 15 vulnerabilities across five security bulletins as part of its September Patch Tuesday release.

After accidentally publicizing the patch details a few days early last week, Microsoft officially released the security bulletins and the accompanying patches on Sept. 13. As was disclosed in the earlier pre-notification announcement, none of the patches in this month's update are considered "critical."

"Though there are no critical updates this month, these vulnerabilities can pave the way for cyber-criminals to execute more severe attacks, such as remote-code execution or remote-information disclosure," Dave Marcus, director of security research and communications at McAfee Labs, told eWEEK.

The bulletin that fixed an arbitrary code execution vulnerability in Excel (MS11-072) was rated as high priority by security researchers. The issue exists in all versions of Excel, including 2010. Attackers could create malicious Excel files to take control of the system just by tricking an unsuspecting user into opening it, according to Wolfgang Kandek, CTO of Qualys.

In light of ongoing spear-phishing and targeted attacks that have used malicious Excel documents and links, the bulletin was "the most relevant and important," Kurt Baumgartner, a senior security researcher at Kaspersky Lab, wrote on the Securelist blog.

The patch fixing the code-execution vulnerability in Microsoft Office versions 2003, 2007 and 2010 (MS11-073), including Microsoft Word, should also be prioritized, according to Kandek. Like the Excel vulnerability, attackers could use a malicious Word file, a common attack vector, to execute code on victims' machines, Kandek wrote on the Laws of Vulnerabilities blog.

Microsoft continued fixing the DLL preloading issue that was identified last year in each of its products. In this update, the issue was fixed in deskpen.dll component (MS11-071). The DLL preloading bug affected all versions of Windows, according to Microsoft's security advisory.

"We've yet to see any exploits targeting one of these vulnerabilities," Joshua Talbot, security intelligence manager of Symantec Security Response, wrote on the Symantec Security Response blog.

The patches for Sharepoint 2007, Sharepoint 2010 and Windows Internet Name Service (WINS) for Windows Server 2003 and Server 2008 fixed elevation-of-privilege issues. Researchers at Core Security Technologies discovered and reported the WINS vulnerability. An attacker could exploit the system running the unpatched WINS service to elevate privileges by sending a user a specially crafted WINS replication packet. The attacker must have valid log-on credentials and be able to log on locally to exploit this vulnerability.

These patches "only apply to certain software configurations," said Tyler Reguly, technical manager of security research and development for nCircle.

Microsoft also released another update revoking six digital certificates signed by Entrust and Cybertrust, who issued them on behalf of the compromised Dutch certificate authority DigiNotar. Microsoft on Sept. 6 moved DigiNotar's root certificates to the Untrusted Certificate Store, which effectively blocks Windows from loading any Website or running any application with a DigiNotar certificate. The company also updated Internet Explorer immediately after the breach at DigiNotar was publicized.

"This update should probably be kept at the top of IT admins' to-do lists-even before any of today's patches-as there are attacks occurring in the wild leveraging the compromised certificates," said Talbot.

Microsoft also reminded its customers that despite the "Comodohacker's" boasts, Windows Update was not compromised by the fake certificates from DigiNotar and can still be trusted.

"Windows Update is not at risk from fraudulent certificates as the update client will only install binaries signed by our own root CA [certificate authority] certificate," said Jerry Bryant, the group manager of Trustworthy Computing at Microsoft.