A Windows feature designed to simplify computing for disabled users could be misused in Vista, a McAfee researcher has reported.

Attackers could use this feature, called StickyKeys, to trick a user into launching unauthorised software on the Vista machine, according to Vinoo Thomas, a McAfee researcher who blogged about the issue on Monday.

StickyKeys is launched when a Windows user hits a modifier key like Shift or Alt five times. This makes the modifier key "sticky" so commands like Shift-F1 can be launched without having to hit two keys simultaneously.

An attacker could replace the sethc.exe file used to launch StickyKeys with some other executable, like the Windows command utility, Thomas wrote.

This backdoor vulnerability was already known to exist in Windows 2000 and Windows XP, according to Thomas.

Although it is interesting that Vista is also vulnerable, it's not clear how useful the backdoor would be to an attacker because one must first gain access to the machine in order to replace the StickyKeys file.

Thomas believes that it could be used by an inside attacker to bypass log-in on terminal servers and workstations.

Microsoft executives were not immediately available to comment on the issue.

To avoid the problem, "one can uninstall the Accessibility Tools feature, which is installed by default, to avoid this fairly simple, yet potentially serious built-in backdoor," he wrote.

"And don't forget to hit the shift key five times and see what pops up on your desktop."

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