CVE-2021-34455 in Windows
Summary
by MITRE • 07/17/2021
Windows File History Service Elevation of Privilege Vulnerability
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Analysis
by VulDB Data Team • 07/17/2021
The Windows File History service vulnerability represents a critical elevation of privilege weakness that allows attackers to escalate their privileges from standard user level to system level execution within Windows operating systems. This vulnerability specifically targets the file history service component that is designed to automatically back up user files to network locations or external storage devices. The flaw exists in how the service handles certain file operations and access controls, creating an exploitable condition where malicious code can manipulate the backup process to gain unauthorized system-level access.
Technical analysis reveals that the vulnerability stems from improper input validation and inadequate privilege separation within the File History service implementation. When users initiate file history backups or when the service processes backup operations, specific file paths or registry entries are not properly sanitized or validated against appropriate access controls. This allows attackers to manipulate the backup destination or configuration parameters to redirect file operations to locations where they can execute arbitrary code with elevated privileges. The flaw is particularly concerning because it leverages legitimate system services that are typically trusted and run with higher privileges than normal user applications, making exploitation more straightforward and less detectable.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with persistent access to target systems. Once successfully exploited, adversaries can maintain long-term presence on compromised machines while having full control over system resources, including the ability to modify or delete critical files, install additional malware, or establish command and control channels. The vulnerability affects multiple Windows versions and is particularly dangerous in enterprise environments where file history services are commonly enabled for data protection purposes. Attackers can exploit this weakness through various vectors including social engineering campaigns that trick users into initiating malicious backup operations or by directly targeting the service configuration files.
Mitigation strategies should focus on implementing proper access controls and monitoring mechanisms around the File History service functionality. Organizations must ensure that automatic backup services are configured with minimal required privileges and that backup destinations are properly secured against unauthorized modifications. System administrators should disable unnecessary file history features when not actively needed and implement strict monitoring for abnormal file access patterns or registry modifications related to backup services. Additionally, regular security updates and patches from Microsoft should be applied promptly to address known vulnerabilities in the file history service implementation. This vulnerability aligns with CWE-276 which addresses improper privilege management and relates to ATT&CK technique T1068 which covers local privilege escalation through service exploitation, emphasizing the need for comprehensive endpoint protection and privilege control measures.