CVE-2021-1670 in Windows
Summary
by MITRE • 01/13/2021
Windows Projected File System FS Filter Driver Information Disclosure Vulnerability This CVE ID is unique from CVE-2021-1663, CVE-2021-1672.
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Analysis
by VulDB Data Team • 10/09/2024
The Windows Projected File System FS Filter Driver Information Disclosure Vulnerability represents a critical security flaw within Microsoft's file system infrastructure that affects multiple Windows operating systems including Windows 10, Windows Server 2016, and Windows Server 2019. This vulnerability resides in the projected file system filter driver component that handles virtualized file system operations and is categorized under CWE-200 Information Disclosure. The flaw stems from improper handling of kernel-mode memory access during projected file system operations, allowing unauthorized information disclosure through specific file system interactions. The vulnerability specifically impacts the fsfilter.sys driver component which manages file system filter operations and is part of the broader Windows kernel security architecture that implements projected file system functionality for applications requiring virtualized file access.
The technical exploitation of this vulnerability occurs when malicious actors leverage specific file system operations that trigger improper memory handling within the fsfilter.sys driver. Attackers can craft crafted file system requests that cause the driver to disclose sensitive kernel memory contents to user-mode applications through information leakage mechanisms. The vulnerability is particularly concerning because it operates at the kernel level where privilege escalation opportunities exist, potentially allowing attackers to extract sensitive system information including memory addresses, kernel structures, and potentially cryptographic keys or credentials. This type of information disclosure vulnerability aligns with ATT&CK technique T1005 which involves data from local system information gathering and T1059 which covers command and scripting interpreter usage for exploitation purposes. The flaw is classified as a privilege escalation vector due to its potential to provide attackers with information that could be used to bypass security controls or conduct more sophisticated attacks.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more severe attacks including privilege escalation and system compromise. When exploited successfully, attackers can gain insights into kernel memory layouts and system configurations that would normally be protected from user-mode access. This information leakage could facilitate advanced exploitation techniques such as heap spraying, kernel address space layout randomization (ASLR) bypasses, and other sophisticated attack methodologies. The vulnerability affects systems where projected file system functionality is actively used, particularly in enterprise environments where virtualized file systems and cloud storage integrations are common. Organizations running servers with file system filter drivers enabled and those utilizing projected file system features are at heightened risk, as the vulnerability can be exploited remotely through network-based attacks or locally through compromised user accounts with appropriate privileges.
Mitigation strategies for this vulnerability require immediate patch application from Microsoft as part of the regular security update cycle, with particular attention to the specific Windows versions affected by CVE-2021-1670. System administrators should ensure that all Windows systems receive the relevant security updates and that organizations implement comprehensive monitoring for suspicious file system activity that might indicate exploitation attempts. Network segmentation and privilege least-privilege principles should be enforced to limit potential attack surface, while security teams should monitor for indicators of compromise related to information disclosure activities. The vulnerability demonstrates the importance of kernel-level security controls and highlights the need for robust memory management practices in operating system components. Organizations should also consider implementing additional security measures such as kernel-mode code integrity checking and advanced threat detection systems that can identify anomalous file system behavior patterns consistent with exploitation attempts. Regular security assessments of file system filter driver configurations and projected file system implementations should be conducted to ensure proper security posture and reduce exposure to similar vulnerabilities in the future.