CVE-2021-41370 in Windows
Summary
by MITRE • 11/10/2021
NTFS Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-41367, CVE-2021-42283.
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Analysis
by VulDB Data Team • 11/11/2021
This vulnerability represents a critical elevation of privilege flaw within the NTFS file system implementation on Windows operating systems. The issue stems from improper handling of certain file system operations that allow unprivileged users to escalate their privileges to SYSTEM level access. The vulnerability specifically affects the NTFS file system's interaction with file permissions and access control mechanisms, creating a pathway for malicious actors to bypass normal security boundaries. Unlike CVE-2021-41367 which targeted different aspects of the file system, and CVE-2021-42283 which focused on Kerberos authentication, this vulnerability directly exploits weaknesses in the NTFS subsystem's privilege management. The flaw manifests when the system processes specific file operations that should require elevated permissions but instead execute with reduced privilege contexts, allowing attackers to manipulate file attributes and access controls in ways that should be restricted.
The technical root cause of CVE-2021-41370 lies in the insufficient validation of access control lists and file permission structures within the NTFS file system driver. When processing certain file operations, the system fails to properly verify that the requesting user has sufficient privileges to perform the requested action, particularly when dealing with file ownership changes and access control modifications. This vulnerability falls under CWE-264, which addresses permissions, privileges, and access control issues, and specifically relates to improper access control mechanisms. The flaw can be triggered through carefully crafted file system operations that exploit the way the NTFS driver handles permission validation during file creation, modification, or attribute changes. Attackers can leverage this by creating specific file structures that, when processed by the system, cause the permission checking logic to be bypassed or incorrectly evaluated.
The operational impact of this vulnerability is severe as it provides attackers with a direct path to SYSTEM-level access without requiring any prior elevated privileges. Once exploited, an attacker can gain complete control over the affected system, including the ability to read, modify, or delete any file regardless of its permissions, and can execute arbitrary code with the highest privilege level available. This allows for complete system compromise, data exfiltration, and persistence establishment. The vulnerability affects multiple Windows versions including Windows 10 and Windows Server 2019, making it particularly concerning for enterprise environments where these systems are prevalent. The attack surface is broad since the flaw can be exploited through various means including local file system operations, network file sharing, and even through certain types of malware that might leverage file system manipulation as part of their attack vectors. The vulnerability's exploitation does not require specialized tools or extensive knowledge of system internals, making it particularly dangerous as it can be leveraged by threat actors with varying skill levels.
Mitigation strategies for CVE-2021-41370 should focus on immediate patch deployment from Microsoft as the primary defense mechanism. Organizations must ensure that all affected systems receive the relevant security updates as soon as they become available, particularly since this vulnerability can be exploited remotely through various attack vectors including file sharing protocols and network-based file operations. System administrators should implement additional monitoring for unusual file system activities, particularly around file creation, modification, and permission changes, as these operations may indicate exploitation attempts. Network segmentation and access control policies should be reviewed and strengthened to limit potential lateral movement if an attacker does manage to exploit the vulnerability. The principle of least privilege should be enforced more rigorously, ensuring that users have only the minimum permissions necessary for their legitimate operations. Additionally, organizations should consider implementing endpoint detection and response solutions that can identify anomalous file system behavior patterns consistent with exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify any systems that may not have received the necessary patches, and incident response procedures should be updated to include specific guidance for handling potential exploitation of this vulnerability. The ATT&CK framework categorizes this as a privilege escalation technique under T1068, and organizations should incorporate this understanding into their threat modeling and defensive strategies to effectively counter potential exploitation attempts.