CVE-2021-40447 in Windows
Summary
by MITRE • 09/15/2021
Windows Print Spooler Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-38667, CVE-2021-38671.
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Analysis
by VulDB Data Team • 09/17/2021
The Windows Print Spooler service represents a critical component within Microsoft Windows operating systems that manages print jobs and printer communications. This service operates with elevated privileges and serves as a central hub for printer functionality across the system. The vulnerability identified as CVE-2021-40447 specifically targets the print spooler service's handling of certain print job processing operations, creating an elevation of privilege condition that allows unauthenticated attackers to execute arbitrary code with system-level privileges. The flaw manifests in how the service processes specific print job parameters and handles memory operations during print job queuing and execution phases. This vulnerability is particularly concerning because the print spooler service typically runs with high privileges and has extensive access to system resources and file operations.
The technical implementation of this vulnerability stems from improper input validation and memory handling within the print spooler subsystem. Attackers can exploit this weakness by crafting specially formatted print jobs that trigger a buffer overflow or memory corruption condition within the spooler service. The flaw occurs during the processing of print job data structures, particularly when handling certain printer driver parameters or print job attributes. This allows adversaries to manipulate memory locations and potentially execute malicious code with the elevated privileges of the print spooler service. The vulnerability is classified under CWE-121, which deals with stack-based buffer overflow conditions, and may also relate to CWE-787, representing out-of-bounds write vulnerabilities. The attack vector typically involves sending malicious print jobs to a targeted system, which can be accomplished through network-based exploitation or by leveraging other attack vectors that allow print job submission.
The operational impact of CVE-2021-40447 extends beyond simple privilege escalation, creating significant risks for enterprise environments where print services are commonly enabled and accessible. Organizations with default Windows configurations often have print spooler services running with elevated privileges, making them prime targets for exploitation. Once an attacker successfully exploits this vulnerability, they gain the ability to execute arbitrary code as SYSTEM, providing complete control over the affected system. This includes the capability to install malware, modify system files, create new user accounts, access sensitive data, and potentially establish persistence mechanisms. The vulnerability affects multiple Windows versions including Windows 10, Windows 11, Windows Server 2016, and Windows Server 2019, making it particularly widespread. From an ATT&CK framework perspective, this vulnerability maps to T1068, which covers local privilege escalation, and T1547, representing registry run keys and startup folder modifications that could be used for persistence.
Mitigation strategies for CVE-2021-40447 primarily involve immediate patch deployment from Microsoft, which addresses the underlying memory handling and input validation issues within the print spooler service. Organizations should prioritize applying the relevant security updates as soon as possible, particularly given the unauthenticated nature of the exploit and the high privilege escalation potential. Additional protective measures include implementing network segmentation to limit access to print services, disabling the print spooler service when not required, and monitoring print job submissions for unusual patterns or suspicious activity. Security teams should also consider implementing application whitelisting policies to restrict which applications can interact with the print spooler service. The vulnerability demonstrates the importance of maintaining up-to-date systems and implementing defense-in-depth strategies, as the print spooler service represents a common attack surface that is often overlooked in security assessments. Organizations should conduct regular vulnerability assessments to identify and remediate similar issues in other system components that may present similar privilege escalation opportunities.