CVE-2021-1654 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-2021-1655, CVE-2021-1659, 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 represents a critical security flaw within the Windows operating system that allows local attackers to escalate their privileges from standard user level to system level execution. This vulnerability specifically targets the Windows Client Server Runtime Subsystem service which handles client-server communication between local and remote processes. The flaw exists in the way the CSC service processes certain authentication requests and manages access controls, creating an opportunity for malicious actors to exploit improper privilege handling mechanisms. This vulnerability is particularly concerning as it operates at the kernel level where unauthorized access can result in complete system compromise and persistent backdoor capabilities.
The technical root cause of CVE-2021-1654 stems from inadequate input validation and privilege checking within the CSC service implementation. When the service processes specific RPC calls or authentication sequences, it fails to properly validate the security context of incoming requests, allowing unprivileged users to manipulate service behavior through crafted input parameters. This flaw falls under the CWE category of improper privilege management, specifically CWE-276, which addresses incorrect permissions for critical resources. The vulnerability enables attackers to leverage the service's elevated privileges to execute arbitrary code with system-level access, bypassing standard Windows security controls including User Account Control and mandatory integrity levels. The exploitation process typically involves sending specially crafted requests to the CSC service that trigger the privilege escalation mechanism, often through manipulation of security descriptors or access token handling.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with persistent access to compromised systems and enables further lateral movement within network environments. Once successfully exploited, attackers can establish persistent backdoors, modify system files, install malware, and access sensitive data without detection. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it particularly dangerous for enterprise environments where these systems are commonly deployed. From an adversary perspective, this vulnerability maps directly to ATT&CK technique T1068, which involves exploiting local privileges to gain system-level access, and T1543, which covers creating or modifying system-level persistence mechanisms. The vulnerability's impact is compounded by the fact that it requires no special privileges to exploit, making it accessible to any user with local access to the affected system.
Mitigation strategies for CVE-2021-1654 should focus on immediate patch deployment and system hardening measures. Microsoft released security updates that address the vulnerability by correcting the privilege validation logic within the CSC service and implementing proper access control checks. Organizations should prioritize patch management procedures to ensure all affected systems receive the relevant security updates promptly. Additionally, system administrators should implement network segmentation to limit local access privileges and monitor for unusual authentication patterns that might indicate exploitation attempts. Security controls should include disabling unnecessary services and implementing strict access controls for the CSC service, particularly when running on systems that do not require client-server communication functionality. The vulnerability also highlights the importance of maintaining up-to-date security monitoring capabilities and implementing behavioral analysis tools that can detect anomalous privilege escalation patterns. Organizations should conduct regular security assessments to identify and remediate similar privilege escalation vulnerabilities in other system components and maintain comprehensive incident response procedures for potential exploitation events.