CVE-2021-34527: What You Need to Know About PrintNightmare

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Web applications are an essential part of modern businesses, but they’re also prime targets for attackers. Over the years, several high-profile vulnerabilities have emerged, putting web applications and their users at risk. In this post, we’ll focus on one such vulnerability, CVE-2021-34527, commonly known as PrintNightmare. We’ll go over the details of the vulnerability and provide steps for testing and defending against it.

What is CVE-2021-34527: PrintNightmare?

CVE-2021-34527, also known as PrintNightmare, is a vulnerability that affects the Windows Print Spooler service. The vulnerability enables an attacker to remotely execute code with system-level privileges, granting them control over an affected system.

How does PrintNightmare work?

The Print Spooler service manages print jobs on a Windows system. The vulnerability arises because the service doesn’t properly validate the permissions of remote print servers. This lets an attacker send a specially crafted print request to the Print Spooler service, which can execute code with system-level privileges.

How to test for PrintNightmare

Follow these steps to test for PrintNightmare:

  1. Open the command prompt on a Windows system.
  2. Type the following command to check if the Print Spooler service is running: 
    sc query spooler
  3. If the service is running, type the following command to stop the service: 
    net stop spooler
  4. Type the following command to start the service again: net start spooler
  5. If the service is vulnerable, the following command can be used to exploit it. 
rundll32 printui.dll,PrintUIEntry /Xg /n\\localhost\test

How to defend against PrintNightmare

Follow these steps to defend against PrintNightmare:

  1. Apply the latest security updates from Microsoft. Microsoft has released several updates to address this vulnerability. Apply these updates to all affected systems as soon as possible.
  2. Disable the Print Spooler service on all systems that don’t need it. This prevents the vulnerability from being exploited.
  3. Configure Windows Firewall to block incoming connections to the Print Spooler service. This can help prevent attackers from exploiting the vulnerability.
  4. Implement the principle of least privilege. Users should have only the permissions needed to perform their job duties. This limits the impact of any potential attack.
  5. Use antivirus software and keep it updated. Antivirus software detects and prevents malicious code from executing on a system.

In conclusion, PrintNightmare is a serious vulnerability that can allow attackers to take control of a Windows system. To defend against this vulnerability, apply the latest security updates, disable the Print Spooler service on non-essential systems, configure Windows Firewall, implement the principle of least privilege, and use up-to-date antivirus software. By following these steps, you can help keep your systems and data secure.