The latest round of monthly patches from Microsoft illustrates the need for organizations to move from older versions of Microsoft software if they haven’t done so already.

”The load of the risk is on older software versions,” said Wolfgang Kandek, chief technology officer for security firm Qualys, about this round of Microsoft software patches.

Overall, Microsoft Patch Tuesday for December addressed a total of 24 vulnerabilities with 11 security bulletins. The bulletins cover Microsoft Windows, Office, Internet Explorer, Exchange, Office365, Visual Studio, and SharePoint.

Microsoft rated five of these bulletins as critical, meaning that the patches they contain should be applied as soon as possible.

Perhaps the set of critical patches that should be applied first is MS13-096, which addresses a vulnerability in Microsoft’s GDI+ library for parsing TIFF image files. It is already being exploited by attackers.

The vulnerability affects mainly older Microsoft software, including Windows Vista, Office 2003, Office 2007, and Office 2010. It is already being used in targeted attacks in the Middle East and Asia.

Kandek noted that newer software tends to have fewer vulnerabilities than older software. “The newer software versions just have more security features. Windows 8.1 has more security features that Windows 8 which has more than Windows 7, which has many more than Windows XP,” he said.

”Even if you are fully patched with Windows XP, you are running more of a risk than with a fully patched Windows 7 installation,” Kandek said.

Win XP still a security risk

As an example, Kandek noted there has another zero-day vulnerability in the Windows XP kernel that this month’s patch cycle has not addressed. A zero-day vulnerability means that exploits have already been crafted that take advantage of a software flaw. In this case, an attacker can send the user a maliciously crafted PDF file that, when opened, can deposit code in the computer’s memory that grants another user administrative access.

Microsoft offers a work-around for this problem.

Qualys estimated that 15 percent of enterprise users are still running Windows XP. T

hough the percentage of XP users is rapidly declining, Kandek doubted that everyone will be off the OS by April 2014, when Microsoft will cease issuing security patches for Windows XP. “After April, these machines will be very quickly be easy targets,” Kandek said.

Another critical set of patches come under the security bulletin MS13-097, which affects Internet Explorer. The bulletin indicated that these vulnerabilities are easy to exploit, such as by using a maliciously crafted webpage.

The third critical bulletin, MS13-105 addresses a number of flaws in Outlook Web Access that an attacker could use to gain access to Microsoft Exchange server by tricking the user into opening a documents with embedded malicious code.

The fourth critical bulletin, MS13-099, affects all desktop and server versions of Microsoft Windows, including Windows RT. This vulnerability, in the Windows Script functionality, allows a remote attacker to gain access to a computer through a website that hosts specially crafted content.

The final critical vulnerability for this month, addressed in MS13-098, allows attackers to add their own malware to software being installed on a computer over a network using the Authenticode signing algorithm.

The remaining bulletins, ranked as important, should be applied in the organization’s usual patch management schedule, Kandek advised. They cover Windows, SharePoint Server, Office and Microsoft Developer Tools.

For the year, Microsoft covered 330 vulnerabilities with 106 bulletins.