The Printnightmare exploit is so scary, even Windows 7 got an emergency fix (but it’s imperfect)

Download it right now.

Microsoft typically releases updates for Windows as part of its monthly “Patch Tuesday” blitz, but the company recently took the unusual step of releasing an emergency out-of-band security update to fix the critical “Printnightmare” vulnerability published (and deleted [ go. pcworld.com/pbdl]) by researchers—even for Windows 7. Bottom line? Update your Windows PC pronto…but the patch may not fix all PCS if your system is connected to a local network.

Printnightmare attacks the Windows Print Spooler service, which runs by default. “A remote code execution vulnerability exists

when the Windows Print Spooler service improperly performs privileged file operations,” Microsoft’s executive summary ( go.pcworld.com/mxsm) states. “An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.”

In other words, Printnightmare lets attackers into your system over the internet, and then they essentially have free rein over your computer. “All supported editions of Windows are affected,” Microsoft warns.

Microsoft initially released emergency security patches for most versions of Windows 10, Windows 8.1, Windows RT 8.1, and various Windows Server installations. In its advisory, Microsoft also suggests making specific changes to registry and Group Policy settings if necessary. Driving home how severe this vulnerability is, the company even released a Printnightmare security fix for Windows 7, an operating system that was forced into retirement last year ( go.pcworld.com/fret).

The company lists these patches as a temporary fix, and security researcher Matthew Hickey ( go.pcworld.com/mhik) says that the patch only nullifies the danger of remote execution. That means that if an attacker manages to physically obtain your PC, they could still leverage Printnightmare to take control of it. (Update: After the patch was released, security researchers discovered that fully patched systems could still be attacked remotely if your administrator enables certain settings to permit a network printer feature called Point and Print, Ars Technica reports [ go.pcworld.com/atrp].) But for the vast majority of people who are simply using personal computers in their home, shutting down the ability for this vulnerability to work over the internet should effectively render it obsolete.

So get to downloading, folks. Checking Windows Update on my PC showed the Printnightmare patch (KB5004945 [ go. pcworld.com/kb50] for my version of Windows 10) already available. While you’re being safety-minded, make sure to install an antivirus program ( go.pcworld.com/inav) and perform the five easy tasks that supercharge your security ( go.pcworld.com/5tsk) if you haven’t done so already.