Microsoft Confirms 'PrintNightmare' Vulnerability Affects All Windows Versions

UPDATE 7/7: Microsoft is starting to roll out patches for the “PrintNightmare” vulnerability. The patches target most versions of Windows, including the latest version of Windows 10 21H1, and Windows 7 Service Pack 1.

Original Story:
Microsoft confirmed that a zero-day vulnerability known as PrintNightmare, which can be exploited to enable remote code execution on a target device, affects every version of Windows.

Sangfor Technologies researchers accidentally published a proof of concept exploit for PrintNightmare via GitHub on June 29. According to MalwareBytes, the researchers believed their exploit was addressed by a June 8 security update to Windows 10 for another vulnerability, CVE-2021-1675. The researchers deleted that repository, but it can still be found online.

Microsoft said in a security bulletin that PrintNightmare, to which it assigned the identifier CVE-2021-34527, is "similar but distinct from the vulnerability that is assigned CVE-2021-1675." It also said attackers can exploit PrintNightmare to "install programs; view, change, or delete data; or create new accounts with full user rights" after gaining SYSTEM privileges on a device.

The vulnerability is found in code related to the Windows Print Spooler executable that handles pretty much every aspect of the process involved with printing something from a PC. Microsoft said that by default Windows Print Spooler launches alongside Windows and only closes when the operating system itself is shut down. That makes it an attractive target for attackers.

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PrintNightmare is already being exploited in the wild, Microsoft said, and the security patches released on June 8 won't fully protect Windows devices from those attacks. That doesn't mean those patches should be avoided—they can still defend against other exploits, including those involving CVE-2021-1675. They just don't fully address exploits involving PrintNightmare.

There are two workarounds for PrintNightmare: Disabling the process using PowerShell, which "disables the ability to print both locally and remotely," or creating a new Group Policy to disable remote printing. Microsoft said that Group Policy setting means a given device "will no longer function as a print server, but local printing to a directly attached device will still be possible."