CVE-2021-34496 in Windows
Summary
by MITRE • 07/15/2021
Windows GDI Information Disclosure Vulnerability
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Analysis
by VulDB Data Team • 07/17/2021
The Windows GDI information disclosure vulnerability identified as CVE-2021-34496 represents a critical security flaw within the Graphics Device Interface component of Microsoft Windows operating systems. This vulnerability resides in the kernel-mode graphics subsystem that handles rendering operations for various graphical elements and user interface components. The flaw allows an attacker to potentially extract sensitive information from kernel memory through improper validation of input parameters within GDI function calls. The vulnerability specifically affects Windows 10 versions 1903, 1909, and 2004, as well as Windows Server 2019 and Windows Server 2016, making it particularly concerning for enterprise environments where these operating systems are prevalent. The issue stems from insufficient bounds checking and validation mechanisms in the GDI driver implementation, which processes graphics-related data structures and commands from user-mode applications.
The technical exploitation of this vulnerability occurs when a malicious application or attacker crafts specific input parameters that trigger improper memory handling within the GDI subsystem. This flaw manifests as an information disclosure vulnerability categorized under CWE-200, which deals with exposure of sensitive information to an unauthorized actor. The vulnerability allows for potential data leakage from kernel memory spaces, which could include sensitive system information, cryptographic keys, or other confidential data that should remain protected from user-mode access. Attackers can leverage this weakness through a local privilege escalation vector, where they first need to execute code in a user context before attempting to exploit the information disclosure mechanism to gain deeper system access. The ATT&CK framework categorizes this vulnerability under T1068, which involves the exploitation of local privilege escalation techniques, and T1552, which covers data harvesting through information gathering methods. The GDI subsystem's handling of graphics objects and their associated metadata creates multiple potential attack surfaces where memory corruption can occur, particularly during the processing of malformed graphics parameters.
The operational impact of CVE-2021-34496 extends beyond simple information disclosure, as the leaked kernel memory contents could provide attackers with critical insights into system internals, memory layouts, and potentially sensitive cryptographic material. This vulnerability significantly increases the risk of subsequent attacks, as the disclosed information could be used to bypass security mitigations such as address space layout randomization or exploit other vulnerabilities in the same subsystem. Organizations running affected Windows versions face substantial risk of privilege escalation attacks, where the information disclosure serves as a stepping stone to more serious compromise scenarios. The vulnerability affects all Windows 10 editions and Windows Server versions that include the affected GDI components, making it particularly dangerous for large enterprise networks where these systems are commonly deployed. Security researchers have noted that the vulnerability is particularly concerning because it can be exploited without requiring special privileges initially, allowing attackers to gather intelligence before attempting more sophisticated attacks.
Mitigation strategies for this vulnerability primarily involve applying the official Microsoft security patches released as part of the June 2021 security updates, which address the underlying GDI validation issues through improved input parameter checking and memory boundary enforcement. Organizations should prioritize patch deployment across all affected Windows systems, particularly those running the vulnerable versions mentioned in the vulnerability description. Additional mitigations include implementing strict application whitelisting policies to limit the execution of potentially malicious code that could exploit this vulnerability, and enabling kernel-mode exploit protection features such as Control Flow Guard and Address Space Layout Randomization. Network segmentation and monitoring for suspicious GDI-related activity can help detect potential exploitation attempts, while regular security assessments should include verification that systems are properly patched and that no unauthorized modifications exist in the GDI subsystem. The vulnerability also underscores the importance of maintaining up-to-date security practices and continuous monitoring of emerging threats within graphics and kernel-mode components of operating systems, as these areas represent significant attack surfaces that require ongoing attention and protection.