CVE-2020-17042: Windows 10 Print Spooler RCE Vulnerability

CVE-2020-17042 Overview

CVE-2020-17042 is a Remote Code Execution (RCE) vulnerability affecting the Windows Print Spooler service across a wide range of Microsoft Windows operating systems. This vulnerability allows an attacker to execute arbitrary code on a target system by exploiting improper handling within the Print Spooler component. The Print Spooler service is enabled by default on Windows systems and manages all print jobs, making this vulnerability particularly concerning for enterprise environments.

Critical Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code with the privileges of the compromised process, potentially leading to full system compromise, data theft, or lateral movement within a network.

Affected Products

• Microsoft Windows 10 (multiple versions including 1607, 1803, 1809, 1903, 1909, 2004, 20H2)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016 (multiple versions including 1903, 1909, 2004, 20H2)
• Microsoft Windows Server 2019

Discovery Timeline

• November 11, 2020 - CVE-2020-17042 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-17042

Vulnerability Analysis

This vulnerability resides in the Windows Print Spooler service (spoolsv.exe), a core Windows component responsible for managing print jobs and printer interactions. The flaw allows remote attackers to achieve code execution through network-based attack vectors, requiring user interaction to trigger the vulnerability.

The Windows Print Spooler has been a historically attractive target for attackers due to its elevated privileges and network accessibility. When exploited, this vulnerability enables attackers to execute code in the context of the SYSTEM account, granting full control over the affected machine.

Root Cause

The vulnerability stems from improper validation of user-supplied input within the Print Spooler service. The specific technical details have not been publicly disclosed by Microsoft (classified as NVD-CWE-noinfo), but the vulnerability class is consistent with other Print Spooler flaws that involve memory corruption or improper object handling during print job processing.

Attack Vector

The attack requires network access to the target system and some form of user interaction. An attacker could exploit this vulnerability by:

1. Crafting a malicious print job or printer configuration that triggers the vulnerability
2. Enticing a user to connect to a malicious print server or open a specially crafted document
3. Leveraging the compromised Print Spooler service to execute arbitrary code with elevated privileges

The network-based attack vector with user interaction requirement means that social engineering or drive-by scenarios are likely exploitation methods. The attacker does not require any prior authentication to the target system.

Detection Methods for CVE-2020-17042

Indicators of Compromise

• Unusual processes spawned by spoolsv.exe (the Print Spooler service)
• Unexpected network connections originating from the Print Spooler process
• Suspicious DLL files being loaded by the Print Spooler service
• Anomalous print job submissions from external or untrusted sources

Detection Strategies

• Monitor Windows Event Logs for Print Spooler service crashes or restarts (Event ID 7031, 7034)
• Deploy endpoint detection rules to identify child processes spawned by spoolsv.exe
• Implement network monitoring to detect unusual SMB traffic related to print operations
• Use SentinelOne's behavioral AI to detect anomalous Print Spooler activity and code execution attempts

Monitoring Recommendations

• Enable verbose logging for the Print Spooler service via Group Policy
• Monitor for unauthorized modifications to print-related registry keys under HKLM\SYSTEM\CurrentControlSet\Control\Print
• Track printer driver installations and updates across the environment
• Implement alerting for Print Spooler service state changes on critical systems

How to Mitigate CVE-2020-17042

Immediate Actions Required

• Apply the Microsoft security update released as part of the November 2020 Patch Tuesday
• Disable the Print Spooler service on systems where printing functionality is not required
• Restrict inbound SMB traffic (port 445) from untrusted networks
• Implement network segmentation to limit lateral movement potential

Patch Information

Microsoft has released security updates to address this vulnerability. Organizations should consult the Microsoft Security Advisory for CVE-2020-17042 for specific patch details and download links for each affected Windows version. The patches should be applied through Windows Update, WSUS, or manual deployment depending on organizational patch management practices.

Workarounds

• Disable the Print Spooler service on domain controllers and servers that do not require print functionality using the command: Stop-Service -Name Spooler -Force; Set-Service -Name Spooler -StartupType Disabled
• Block inbound connections to the Print Spooler service via Windows Firewall rules
• Implement Point and Print restrictions via Group Policy to prevent users from connecting to untrusted print servers
• Use application control policies to restrict DLL loading within the Print Spooler context

# Disable Print Spooler service via PowerShell
Stop-Service -Name Spooler -Force
Set-Service -Name Spooler -StartupType Disabled

# Verify service is stopped
Get-Service -Name Spooler | Select-Object Name, Status, StartType