Windows Kernel Flaw Allows Privilege Elevation

A newly patched vulnerability in the Windows kernel opens enterprise systems to a significant threat of attacks from employees and others able to log on at a system keyboard.

Microsoft released a bulletin and patch Wednesday for a problem with the way the Windows kernel passes error messages to a debugger. The Windows kernel fails to limit the size of messages it passes to the debugger, making it possible for a maliciously crafted message to overrun the debugger's buffer. Properly exploitation by a user with keyboard log-on rights could allow privilege elevation, code execution, data corruption and other ills.

"For example, the attacker could execute code that could allow adding accounts with administrative privileges, deleting critical system files or changing security settings," according to Microsoft security bulletin MS03-013. The problem is rated as "Important," the second-most severe rating on Microsoft's threat scale. Microsoft encourages customers to install the patch at the earliest opportunity.

The flaw affects Windows NT 4.0, Windows NT 4.0 Terminal Server Edition, Windows 2000 and Windows XP. "The systems most likely to be affected by this vulnerability are client systems and terminal servers, which regularly allow end users access to the system directly," Microsoft's bulletin said.

Servers, other than terminal servers, are unlikely to be affected as they are normally configured to restrict interactive log on.

Patches were available for each affected version of Windows.

The bulletin is available at

About the Author

Scott Bekker is editor in chief of Redmond Channel Partner magazine.

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