CVE-2021-1659 in Windows
Summary
by MITRE • 01/13/2021
Windows CSC Service Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-1652, CVE-2021-1653, CVE-2021-1654, CVE-2021-1655, CVE-2021-1688, CVE-2021-1693.
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Analysis
by VulDB Data Team • 10/09/2024
The Windows CSC Service Elevation of Privilege Vulnerability identified as CVE-2021-1659 represents a critical security flaw within the Windows operating system's Client Server Runtime Subsystem service. This vulnerability specifically affects the handling of file system permissions and access controls within the CSC service, which is responsible for managing client-side caching of user profiles and system resources. The flaw exists in the way the service processes and validates file access requests, creating an opportunity for unauthorized privilege escalation. The vulnerability is particularly concerning because it allows a local attacker with limited user privileges to potentially gain elevated system-level access through manipulation of the CSC service's file handling mechanisms.
The technical implementation of this vulnerability stems from improper validation of file paths and access tokens within the CSC service execution context. When the service processes user profile data or system resources, it fails to properly sanitize input parameters that control file access operations. This weakness creates a path traversal scenario where malicious input can bypass normal access controls and potentially allow arbitrary file operations. The flaw manifests when the service attempts to resolve file paths that contain specially crafted sequences or symbolic links, enabling an attacker to manipulate the service's behavior and gain access to restricted system resources. This issue falls under the CWE category of CWE-22 Path Traversal and CWE-787 Out-of-bounds Write, as it involves improper input validation and potential memory corruption scenarios.
From an operational impact perspective, this vulnerability presents a significant risk to enterprise environments where multiple users interact with Windows systems. Attackers can exploit this weakness to elevate their privileges from standard user level to system administrator level, potentially compromising entire networks through lateral movement and persistent access. The vulnerability affects Windows 10 and Windows Server versions, with particular concern for systems running in enterprise environments where user account control may be less restrictive. Once exploited, the attacker can access sensitive system files, modify critical registry entries, install malicious software, and potentially establish backdoors for continued access. The attack vector requires local system access but does not need network connectivity, making it particularly dangerous in environments where physical access is possible or where other vulnerabilities have already been exploited.
Mitigation strategies for CVE-2021-1659 should focus on immediate patch application and system hardening measures. Microsoft released security updates that address this vulnerability through proper input validation and enhanced access control mechanisms within the CSC service. Organizations should prioritize deployment of the relevant security patches as soon as possible, particularly in environments where physical security controls may be inadequate. System administrators should implement additional monitoring for unusual file access patterns and process execution involving the CSC service. The vulnerability aligns with ATT&CK technique T1068, which covers Local Privilege Escalation, and T1547.001, which involves Registry Run Keys. Additional defensive measures include restricting user privileges, implementing least-privilege principles, and configuring appropriate file system permissions to limit the impact of potential exploitation. Security teams should also consider implementing application control policies that restrict execution of unauthorized processes within the CSC service context, as this vulnerability can be leveraged as part of broader attack chains that include initial access and persistence mechanisms.