Patch Tuesday: Malicious fonts bedevil Microsoft Windows

Microsoft fixes multiple vulnerabilities in how the company's software renders TrueType fonts

By , IDG News Service |  Security

Of the six critical security bulletins Microsoft issued in its Patch Tuesday monthly release of software updates, three address a vulnerability in how Microsoft software renders fonts.

"Fonts have become really complicated," said Wolfgang Kandek, chief technology officer for compliance and security software company Qualys. "There is real processing going on when you print a character, and that complexity can be attacked."

The number of critical bulletins Microsoft released this month is a bit higher than normal, Kandek said. Typically, Microsoft will issue about two or three critical bulletins on Patch Tuesday, which occurs on the second Tuesday of each month. This month half the bulletins -- MS13-052, MS13-053 and MS13-054 -- address how Microsoft systems handle the rendering of TrueType fonts.

With this vulnerability, an attacker can embed malicious values in a font description that would overrun the memory allocated to the font-drawing routine, and write into sections of memory reserved for other operations. The font instructions could be provided to Windows or Internet Explorer (IE) by way of a Web page or a document.

"Depending on where this happens, this can be quite serious," Kandek said.

Windows, for instance, renders all characters onto the screen as a system user, not as a standard user, which has fewer system privileges. An exploit of a font-rendering vulnerability could "go right into the operating system and take control at that level," Kandek said.

Overall, Microsoft issued six critical bulletins, covering Windows OS, the .NET Framework, Silverlight, Office, Visual Studio, Lync and IE. A seventh bulletin, labeled as important, covers the Windows Defender security software.

All six of the critical bulletins include remote code execution vulnerabilities, which can be used to provide attackers with illicit access to machines.

Seventeen of the 34 vulnerabilities covered in the bulletins address IE. "Researchers continue to find flaws in IE, and the attack surface is pretty big," Kandek said, referring to how Microsoft is now supporting five different versions of the browser. The vulnerabilities affect IE versions six through 10 that run on Windows XP, Windows Vista, Windows 7, Windows 8, Windows Server 2003, Windows Server 2008 and Windows RT.

"The major problem there is that users or companies still maintain old versions of the browser. We would be better off if everyone was on the newer version" of IE, Kandek said.

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