2021 PrintNightmare Vulnerability Exposes Deep-Rooted Security Flaws in Microsoft’s Print Spooler Service

The 2021 PrintNightmare vulnerability exposed multiple deep-rooted security flaws in Microsoft’s Print Spooler service, a core Windows component. The flaws, which had persisted in the Print Spooler for years, forced Microsoft to change the default behavior of the service, and organizations to change how they enabled printing services for users. While Microsoft’s changes have overall improved Print Spooler’s security, researchers caution the service still remains a prime target for attackers. The potential weaknesses resulting from Microsoft’s efforts to maintain backward compatibility with legacy code leaves Print Spooler vulnerable.

A Critical Security Weakness

The PrintNightmare vulnerability exposed multiple deep-rooted security flaws in Microsoft’s Print Spooler service, a core Windows component. The flaws, which had persisted in the Print Spooler for years, forced Microsoft to change the default behavior of the service, and organizations to change how they enabled printing services for users. While Microsoft’s changes have overall improved Print Spooler’s security, researchers caution the service still remains a prime target for attackers. The potential weaknesses resulting from Microsoft’s efforts to maintain backward compatibility with legacy code leaves Print Spooler vulnerable.

Recommendations for Securing Print Spooler

To secure Print Spooler, security administrators should consider the following recommendations:

• Deploy endpoint controls to prevent unauthorized code execution.
• Restrict network access and segment networks with print servers.
• Enable secure RPC over SMB for the print spooler.
• Disable legacy protocols and features such as SMBv1.
• Enforce strong authentication mechanisms.

Best Practices for Securing Print Spooler

According to experts, disabling Print Spooler services is not feasible in its entirety. However, ensuring that security updates are being applied, which often include changes like the ones noted in the July 2021 out-of-band release for PrintNightmare, is the best way to safeguard against these attacks.