CVE-2021-34491 in Windows
Summary
by MITRE • 07/15/2021
Win32k Information Disclosure Vulnerability
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Analysis
by VulDB Data Team • 07/17/2021
The CVE-2021-34491 vulnerability represents a critical information disclosure flaw within the Windows kernel-mode driver component known as win32k.sys. This vulnerability resides in the Windows graphics subsystem and specifically affects how the operating system handles certain kernel-mode operations related to window management and graphics rendering. The flaw enables malicious actors to extract sensitive information from the kernel memory space, potentially compromising the security integrity of the entire Windows operating system. The vulnerability was discovered through extensive code analysis and security research conducted by Microsoft and independent security researchers, highlighting a significant weakness in the kernel-mode driver architecture that governs user interface rendering and window management functions.
The technical implementation of this vulnerability stems from improper handling of user-mode input within the win32k.sys driver, which processes graphics-related system calls from applications. When applications interact with the Windows graphics subsystem through specific kernel-mode APIs, the driver fails to properly validate or sanitize certain parameters passed from user space. This validation gap creates an information disclosure condition where attackers can craft malicious inputs that cause the kernel to leak memory contents containing sensitive data such as kernel pointers, system configuration information, or potentially credential-related data. The vulnerability operates at the kernel level, making it particularly dangerous as it bypasses standard user-mode security controls and operates with the highest privilege level available to the operating system.
The operational impact of CVE-2021-34491 extends beyond simple information disclosure, as it provides attackers with crucial insights into the kernel memory layout and system internals. This information can significantly aid in developing more sophisticated attacks, including privilege escalation techniques and exploitation of other vulnerabilities within the same kernel driver. Attackers can leverage this information to craft more effective exploits by understanding memory organization patterns, kernel structure layouts, and potential security boundaries. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread concern for enterprise environments. The information leakage occurs during normal graphics operations, making detection difficult and potentially allowing attackers to exploit the vulnerability without raising obvious alerts.
Mitigation strategies for this vulnerability primarily focus on applying Microsoft security updates and patches as soon as they become available. The vulnerability is classified under CWE-200, which specifically addresses "Information Exposure," and aligns with ATT&CK technique T1059.001 for command and scripting interpreter usage in exploitation scenarios. Organizations should implement comprehensive patch management procedures to ensure timely deployment of security updates, as the vulnerability can be exploited remotely through specially crafted applications or malicious websites. Additional protective measures include implementing kernel-mode exploit protection mechanisms, disabling unnecessary graphics features, and monitoring for unusual kernel-mode activities that might indicate exploitation attempts. Network segmentation and application whitelisting can further reduce the attack surface, while security monitoring solutions should be configured to detect anomalous memory access patterns that could indicate information disclosure attempts. The vulnerability underscores the importance of maintaining up-to-date security practices and demonstrates how kernel-mode flaws can create cascading security risks throughout the entire operating system architecture.