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Print Nightmare: How to fix the Windows security bug

Microsoft has just released an exceptional update to fix a critical security flaw PrintNightmare that affects the Windows Print Spooler in several versions of Windows, even Windows 7. Here’s a patch to apply urgently.

How to fix PrintNightmare vulnerability?

At the end of June, security researchers from Sangfor Technologies revealed the existence of a critical flaw affecting several versions of Windows including Windows 7. Called PrintNightmare, this vulnerability is located in the print spooler, the system service that puts documents to be printed on hold (see our useful guide How to enable/disable the print spooler service), and allows hackers to easily execute remote code. After having minimized the importance of this breach, stamped CVE-2021-34527, Microsoft has recognized its danger. Especially since the researchers of Sangfor had by mistake published on the Net the test code allowing to exploit this "0-day" flaw and that some people were quick to use it.

To prevent PrintNightmare from doing massive damage, Microsoft had to urgently develop a patch for all affected Windows versions, namely Windows 10 21H1, 20H1, 2004, 1909, 1809, 1803, and even 1507, Windows 8.1, Windows 7 SP1 - although officially abandoned -, Windows Server 2019, 2012, 2008 R2 SP1 and 2008 SP2. And in an exceptional way, the editor did not wait for its traditional monthly patch package - the famous Patch Tuesday - to release it since it is already available via Windows Update.

If you haven't already done so, install the security update for your version of Windows without delay.

  • To do this, open the Windows settings with the keyboard shortcut Windows + I, click on Update and Security, and then on Windows Update in the left column.
  • Normally, the update should appear at the top, in the Available Updates section. Simply click on the Install now button to retrieve and install it. If it does not appear, click on Check for updates.

  • When the installation is complete, click the Restart now button to apply the patch and restart the system.

Here is the list of updates (KBXXXXX) corresponding to each version of Windows concerned.

  • Windows 10 21H1, 20H2 or 2004 (KB5004945)
  • Windows 10 1909 (KB5004946)
  • Windows 10 1809 and Windows Server 2019 (KB5004947)
  • Windows 10 1803 (KB5004949)
  • Windows 10 1507 (KB5004950)
  • Windows 8.1 and Windows Server 2012 (monthly KB5004954 or Security only KB5004958)
  • Windows Server 2008 SP2 (monthly KB5004955 or Security only KB5004959)
  • Windows 7 SP1 and Windows Server 2008 R2 SP1 (monthly KB5004953 or Security only KB5004951)

Photo – microsoft.com; 123rf.com

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This document, titled « Print Nightmare: How to fix the Windows security bug », is available under the Creative Commons license. Any copy, reuse, or modification of the content should be sufficiently credited to CCM (ccm.net).
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