CVE-2021-40475 in Windows
Summary
by MITRE • 10/13/2021
Windows Cloud Files Mini Filter Driver Information Disclosure Vulnerability
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Analysis
by VulDB Data Team • 10/15/2021
The Windows Cloud Files Mini Filter Driver Information Disclosure Vulnerability represents a critical security flaw within the Windows operating system's cloud storage infrastructure. This vulnerability exists in the cloud files mini filter driver component that facilitates integration between local file systems and cloud storage services such as OneDrive and SharePoint. The mini filter driver operates at a low level within the Windows kernel, intercepting file system operations to enable seamless cloud synchronization and offline access to files. When exploited, this vulnerability allows unauthorized access to sensitive information that should remain protected within the system's memory space. The flaw specifically affects how the driver handles certain file operations and metadata processing, creating potential pathways for information leakage that could compromise user data and system integrity. This vulnerability impacts all supported versions of Windows 10 and Windows 11, making it particularly concerning given the widespread adoption of these operating systems. The information disclosure occurs through improper handling of memory structures during file processing operations, potentially exposing file paths, metadata, and other sensitive data that should remain isolated within the driver's protected memory space. The vulnerability is particularly dangerous because it operates at the kernel level where privileges are highest, allowing attackers to extract information that could be used for further exploitation or targeted attacks against users.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the cloud files mini filter driver. The flaw manifests when the driver processes specific file system requests that involve cloud file synchronization operations, particularly during the handling of file attributes and metadata. The driver fails to properly validate or sanitize certain parameters passed during file operations, leading to information leakage through memory corruption or improper access control mechanisms. This type of vulnerability aligns with CWE-200, which describes improper information disclosure issues in software systems. The vulnerability can be triggered through various file system operations including file creation, modification, and access requests that involve cloud-enabled files. Attackers can potentially leverage this flaw to extract sensitive data such as file names, directory paths, user identifiers, and other metadata that should remain protected within the system's kernel memory. The information disclosure occurs because the driver does not properly enforce access controls on memory segments that contain sensitive operational data. This creates a situation where unprivileged users or malicious processes can potentially access kernel memory regions that contain information about file system operations and cloud synchronization activities.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates potential attack vectors for more sophisticated exploitation techniques. An attacker who successfully exploits this vulnerability could gain insights into the file system structure, cloud synchronization patterns, and user file access behaviors that could be leveraged for targeted attacks. The exposure of file paths and metadata could enable reconnaissance activities that help attackers identify valuable targets within the system. This information could be used to craft more effective phishing campaigns, identify sensitive files for targeted attacks, or map out the cloud storage environment to plan further exploitation. The vulnerability also has implications for enterprise security environments where cloud synchronization is extensively used, as it could expose internal file structures and access patterns that should remain confidential. The potential for privilege escalation exists if the information disclosure can be combined with other vulnerabilities, allowing attackers to move laterally within the system or gain elevated privileges. This vulnerability affects the fundamental security model of Windows cloud integration, potentially undermining the trust model that users expect when syncing files between local systems and cloud services.
Mitigation strategies for this vulnerability should focus on immediate patching and system hardening measures. Microsoft has released security updates that address this specific flaw through kernel-level patches that correct the memory handling and validation issues within the cloud files mini filter driver. Organizations should prioritize deployment of these updates across all affected Windows systems to prevent exploitation. Additionally, network monitoring should be enhanced to detect unusual file system access patterns that might indicate exploitation attempts. The implementation of least privilege principles should be enforced to limit access to cloud synchronization features where possible. Security professionals should also consider implementing additional monitoring for kernel-level memory access patterns and file system operations that could indicate exploitation attempts. System administrators should review cloud storage configurations to ensure that only necessary files are synchronized and that appropriate access controls are in place. This vulnerability demonstrates the importance of proper kernel memory management and input validation, as highlighted by ATT&CK technique T1068 which covers local privilege escalation techniques. Organizations should also consider implementing security awareness training to help users recognize potential exploitation attempts that might leverage information disclosure vulnerabilities. The vulnerability serves as a reminder of the critical nature of kernel-level security components and the potential impact of flaws in system integration layers that connect local and cloud storage environments.