Mitigate PrintNightmare (CVE-2021-34527) in Windows Environments

PrintNightmare is a critical remote code execution and privilege escalation vulnerability affecting the Windows Print Spooler service. Attackers can exploit vulnerable systems to execute arbitrary code with SYSTEM privileges, making domain controllers and print servers particularly attractive targets.

The most effective mitigation is to install the latest Microsoft security updates and disable the Print Spooler service on systems that do not require printing, especially Domain Controllers.

Implementation Steps

• Install the latest Microsoft security updates on all Windows systems.
• Disable the Print Spooler service on Domain Controllers and servers that do not require printing.
• Restrict printer driver installation to administrators only using Group Policy.
• Enable Point and Print restrictions to prevent untrusted driver installation.
• Review administrative privileges and remove unnecessary local administrator accounts.
• Monitor Windows Event Logs for suspicious Print Spooler activity.
• Regularly verify that systems remain fully patched.

Best Practices

• Maintain an accurate inventory of systems running the Print Spooler service.
• Use least privilege principles for printer administration.
• Continuously monitor for newly disclosed Windows vulnerabilities.
• Include Print Spooler configuration checks in your regular Windows hardening baseline.

For additional Windows security recommendations, review other Windows Hardening guidance available on Hardenly.