CVE-2021-1688 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-2021-1659, 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 attackers to escalate their privileges from standard user level to system level access. This vulnerability specifically targets the Windows Client Server Runtime Subsystem service which manages client-server communication between local and remote processes. The flaw exists in how the service handles certain privilege checks during process initialization and communication establishment, creating an exploitable condition that bypasses normal access controls. Unlike related vulnerabilities such as CVE-2021-1652 through CVE-2021-1693 which address different components of the Windows privilege escalation landscape, this particular vulnerability focuses on the CSC service implementation that serves as a bridge for various system operations. The vulnerability falls under the Common Weakness Enumeration category of CWE-276, which encompasses improper privileges and access control mechanisms. This classification aligns with the ATT&CK framework's privilege escalation tactics where adversaries seek to gain elevated system privileges to execute malicious code with higher permissions. The vulnerability is particularly concerning because it can be exploited by local users who do not possess administrative rights, making it a significant threat vector for both internal and external attackers.
The technical implementation of this vulnerability stems from improper validation of access tokens and security descriptors within the CSC service runtime environment. When applications attempt to communicate with the CSC service through specific API calls, the service fails to properly verify the security context of the calling process. This occurs during the initialization phase where the service accepts and processes client connection requests without adequate verification of the requesting process's privileges. The flaw allows an attacker to manipulate the security context of their process to appear as if it has higher privileges than it actually possesses. This misconfiguration enables the service to grant access to system resources and functionality that should only be available to processes running with elevated privileges. The vulnerability is particularly dangerous because it leverages legitimate system components rather than requiring the installation of additional malicious software. Attackers can exploit this by creating specific process sequences that manipulate the CSC service's internal state, effectively bypassing the normal Windows security model. The exploit requires minimal privileges initially but can lead to complete system compromise through privilege escalation.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it can enable attackers to gain complete control over affected systems. Once exploited, attackers can modify system files, install malicious software, access sensitive data, and establish persistence mechanisms within the target environment. The vulnerability affects multiple Windows versions including Windows 10 and Windows Server 2019, making it a widespread threat across enterprise environments. Organizations that rely on standard user accounts for day-to-day operations face significant risk since this vulnerability can be exploited without requiring administrative credentials. The attack surface is particularly broad because the CSC service is frequently used by various legitimate applications and system processes, increasing the likelihood of successful exploitation. Security researchers have noted that this vulnerability can be combined with other techniques to create more sophisticated attack chains, potentially leading to complete network compromise. The vulnerability's impact is further amplified by the fact that it can be exploited remotely through various attack vectors, including network-based attacks that do not require physical access to the target system.
Mitigation strategies for this vulnerability require immediate attention from system administrators and security teams. Microsoft has released security patches that address the underlying privilege validation issues within the CSC service, making it essential for organizations to apply these updates promptly. The recommended approach includes implementing a comprehensive patch management process that ensures all Windows systems receive the latest security updates. Organizations should also consider implementing additional security controls such as enabling Windows Defender Application Control to restrict unauthorized code execution and implementing network segmentation to limit potential attack paths. System administrators should monitor for suspicious process behavior related to CSC service interactions and implement logging controls to detect potential exploitation attempts. The vulnerability highlights the importance of maintaining current security baselines and conducting regular vulnerability assessments to identify similar privilege escalation issues. Security teams should also consider implementing behavioral monitoring solutions that can detect anomalous privilege escalation patterns. Additionally, organizations should review their user access policies and ensure that standard users have minimal necessary privileges to reduce the potential impact of successful exploitation attempts. The remediation process should include comprehensive testing of patches in controlled environments before widespread deployment to avoid potential compatibility issues with existing applications.