Microsoft.scIf your computer is supported by Windows Vista or any later version (including the most recent one, Windows 10), do not postpone your next Microsoft update.

The software behemoth announced yesterday that its next monthly security update will include a patch for a “critical” flaw that, if exploited, would allow a hacker to take control of a system remotely, and install malicious software that could be utilized to delete or modify data, and/or create new user accounts that would also have full user rights. Windows users that are logged in as administrator are the most vulnerable.

This vulnerability was discovered by a security researcher at Vectra Networks, Nicolas Beauchesne, who explained the flaw on his blog. He stated that the attack is made possible by the fact that Windows’ print spooler service is not able validate print drivers properly when they are installed on a computer. The software was designed this way to make printing easier; User Account Controls will generally warn users by asking for admin permission before allowing new drivers to be installed. But because that can delay printing, a decision was made to avoid that control on the print function. That decision essentially transforms “a printer in an internal drive-by exploit kit.”

“So in the end,” Beauchesne concluded, “we have a mechanism that allows downloading executables from a shared drive, and run them as system on a workstation without generating any warning on the user side. From an attacker perspective, this is almost too good to be true, and of course we had to give it a try.”

Fortunately, Microsoft has fixed the vulnerability by providing a patch, which can be downloaded using through the normal Windows Updates.

While the patch is definitely a step in the right direction, Beauchesne also recommends that users “should probably apply the same level of security to printers as we would for other critical infrastructure in networks, such as Active Directory and update servers.”

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