In its May “Patch Tuesday,” Microsoft released seven bulletins covering 23 vulnerabilities

Microsoft has fixed 23 vulnerabilities in its software products, including several considered critical, the company said on Tuesday in its monthly security patch report.

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The security holes, included in seven bulletins, affect Office, Windows, .Net Framework and Silverlight, and in the worst-case scenarios could give attackers control of affected systems, including the ability to run malicious code remotely on them.

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The first critical bulletin covers a vulnerability in Microsoft Office that could allow attackers to execute remote code on compromised systems. For that to happen, users would have to open an infected rich-text format (RTF) file. If successful, the exploit would give attackers the same usage rights as the current user.

The issue is labeled critical for all supported editions of Microsoft Word 2007. It is rated “important” — the second highest severity level in Microsoft’s four-level scale — for all supported editions of Word 2003, Office 2008 for Mac and Office for Mac 2011, as well as all supported versions of Office Compatibility Pack. The security hole was privately reported to Microsoft.

The second critical bulletin involves 10 vulnerabilities in Office, Windows, .NET Framework, and Silverlight, seven of which were privately reported to the company. The most dangerous vulnerability would let attackers run code remotely on an affected user’s machine if the user opens an infected document or is tricked into visiting a malware-laden webpage with embedded TrueType font files.

The problem is rated critical for all supported editions of Windows, .Net Framework 4 (except when installed on Windows editions for Itanium chips); and Silverlight 4 and 5. It’s considered important for Office 2003, Office 2007 and Office 2010.

Commenting on this bulletin in a separate blog post, Jonathan Ness, from the Microsoft Security Response Center Engineering team, said that since fixing a vulnerability five months ago that was being exploited by the Duqu malware through malicious Office documents, Microsoft found that the problematic Microsoft code, win32k.sys, was in other products as well.

Fixing the vulnerabilty, an insufficient bounds check within the font parsing subsystem of win32k.sys, in the newly-discovered places led Microsoft to include several products in this bulletin and consolidate a variety of other fixes in it, according to Ness.

The third critical bulletin covers two privately-reported vulnerabilities in .Net Framework that could open the door for attackers to execute code remotely on the infected machine with the same level of rights as the affected user. For the exploit to be successful, users would need to visit an infected webpage using a browser that can run XAML Browser Applications (XBAPs).

This security update is considered critical for all supported editions of the Microsoft .NET Framework on all supported editions of Microsoft Windows.

The four bulletins labeled important include one that covers six Office vulnerabilities that could allow remote code execution if users open an infected Office file. This fix is considered important for all supported editions of Excel 2003, Excel 2007, Office 2007, Excel 2010, Office 2010, Office 2008 for Mac, and Office for Mac 2011, as well as for supported versions of Excel Viewer and Office Compatibility Pack.

Another important bulletin addresses one vulnerability in Visio Viewer 2010 that could give attackers the ability to execute malicious code remotely if users open an infected Visio file.

The third bulletin tagged as important deals with two security holes in Windows, including one affecting the TCP/IP component that could allow an attacker that logs on to a system to upgrade his user access privileges by running a specially crafted application. This hole is considered important for all supported editions of Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2.

The final bulletin also involves Windows, specifically its Windows Partition Manager and a vulnerability that could let an attacker who gains access to a system to run a malicious application to elevate his user access privileges. The attacker needs to have valid credentials to access the system, and must log on manually on the affected machine. This issue is considered important for all supported editions of Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2.

Users who have their machines set up to receive Microsoft’s software patches automatically don’t need to do anything. The fixes will be installed on their computers automatically. The updates can also be manually downloaded at the Microsoft Update and Windows Update sites.

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