CVE-2021-34527

Обходное решение

Determine if the Print Spooler service is running

Run the following in Windows PowerShell:

Get-Service -Name Spooler

If the Print Spooler is running or if the service is not set to disabled, select one of the following options to either disable the Print Spooler service, or to Disable inbound remote printing through Group Policy:

Option 1 - Disable the Print Spooler service

If disabling the Print Spooler service is appropriate for your enterprise, use the following PowerShell commands:

Stop-Service -Name Spooler -Force

Set-Service -Name Spooler -StartupType Disabled

Impact of workaround Disabling the Print Spooler service disables the ability to print both locally and remotely.

Option 2 - Disable inbound remote printing through Group Policy

You can also configure the settings via Group Policy as follows:

Computer Configuration / Administrative Templates / Printers

Disable the “Allow Print Spooler to accept client connections:” policy to block remote attacks.

You must restart the Print Spooler service for the group policy to take effect.

Impact of workaround This policy will block the remote attack vector by preventing inbound remote printing operations. The system will no longer function as a print server, but local printing to a directly attached device will still be possible.

For more information see: Use Group Policy settings to control printers.

FAQ

If I have not yet installed the security update released Out-of-Band on July 6 and 7, 2021, then do I need to install both the Out-of-Band security update released on July 6 and 7, 2021, and the monthly security updates released on July 13, 2021 to be protected from PrintNightmare?

All monthly security updates are cumulative, including the monthly security updates released on July 13, 2021. The July 13, 2021 cumulative security updates contain all previous security fixes - including the security fix for the print spooler vulnerability (CVE-2021-34527). Customers who have not previously deployed the OOB fix released on July 6 and 7, 2021, can skip deploying the OOB update and deploy the July cumulative security updates released on July 13, 2021, to be protected.

Is this the vulnerability that has been referred to publicly as PrintNightmare?

Yes, Microsoft has assigned CVE-2021-34527 to this vulnerability.

Is this vulnerability related to CVE-2021-1675?

This vulnerability is similar but distinct from the vulnerability that is assigned CVE-2021-1675. The attack vector is different as well. CVE-2021-1675 was addressed by the security update released on June 8, 2021.

Did the June 2021 update introduce this vulnerability?

No, the vulnerability existed before the June 8, 2021 security update.

All versions of Windows are listed in the Security Updates table. Are all versions vulnerable?

All versions of Windows are vulnerable. As of July 7, 2021, Microsoft has released security updates for this vulnerability for all supported versions of Windows listed in the security updates table in this CVE.

What vulnerabilities do the security updates released on and after July 6, 2021 address?

The security updates released on and after July 6, 2021 contain protections for a remote code execution exploit in the Windows Print Spooler service known as “PrintNightmare”, documented in CVE-2021-34527, as well as for CVE-2021-1675.

Are Domain Controllers known to be affected by the vulnerability?

Domain controllers are affected if the print spooler service is enabled.

Are client systems and member servers that are not domain controllers known to be affected by the vulnerability?

Yes. All editions of Windows are affected.

How can I see attack activity on my network related to this vulnerability?

Security products, like Microsoft 365 Defender, offer different ways to view relevant alerts and telemetry. Microsoft has published our recommendations for seeing this sort of behavior at our GitHub here: Microsoft 365 Defender Hunting Queries. Customers using other technologies can adapt this logic for use in their environments.

How is Point and Print technology affected by this particular vulnerability?

Point and Print is not directly related to this vulnerability, but certain configurations make systems vulnerable to exploitation.

How does Microsoft recommend implementing Point and Print restrictions to help secure my systems?

Please see KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates for complete information.

How do I assess my Point and Print security posture to determine if my Windows system is affected by this particular configuration?

Please see KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates for complete information.