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More Windows Kernel Vulnerabilities May Yet Emerge, Researcher Says

After issuing dozens of patches this year, Microsoft could still have more work to do, Black Hat speaker warns
A researcher who discovered a fundamental design flaw in the kernel of the Windows operating system says the software giant has done a good job of patching so far, but it's likely that more vulnerabilities will emerge before its work is done.

Tarjei Mandt, a researcher at security company Norman ASA, says that despite last week's Patch Tuesday announcements, which corrected some 13 Windows kernel vulnerabilities -- and a series of patches issued in April that patched 30 more, there likely will be more vulnerabilities found at the Windows kernel level.

Mandt, who discovered the fundamental flaws in the 15-year-old Win32.sys operating environment, will present his findings on Windows kernel vulnerabilities in a talk that will be presented at Black Hat USA in Las Vegas next month.

The vulnerabilities -- and Mandt estimates there could be hundreds of them -- generally are the result of a function in the Win32k graphical user interface called user-mode callbacks, a mechanism that allows the kernel to make calls back into user-mode. User-mode callbacks enable the operating system to do a variety of tasks, such as invoking application-defined hooks, providing event notifications, and copying data to or from user-mode, Mandt explains.

While there are no known examples of exploits that take advantage of the Win32k vulnerabilities in the wild, the relative ease of creating such exploits -- combined with the fundamental role of the kernel in all Windows operations -- should make these vulnerabilities a top priority for patching, Mandt says.

"A flaw at the kernel level could give an attacker access to some capabilities that an application-level flaw might not," Mandt says. One of the principal threats is the ability to use the flaws to elevate user privileges, which could enable the attacker to take over a Windows device and/or execute code remotely.

By issuing 30 patches in April and another 13 last week, Microsoft has taken some strong steps in fixing the problem, Mandt says. But because flaws at the graphical user interface (GUI) level are so fundamental to the operating system, recognizing and patching them all will be a complex process, he warns.

"It's hard to say if Windows is OK at this point," Mandt says. "The problems are very complex. There probably will be more bugs, but it's hard to say how many. It's something we'll be watching closely."

Norman ASA, which makes a variety of tools ranging, from simple antivirus applications to complex malware analysis environments, specializes in Windows kernel-level security issues and tools.

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