CVE-2021-1655 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-2021-1659, 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 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 CSC service handles certain privilege checks during process execution, creating an opportunity for malicious actors to bypass normal security restrictions. The vulnerability is particularly concerning because it operates at the kernel level where standard user privileges are typically insufficient to perform privileged operations. This issue affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread concern for enterprise environments. The vulnerability is classified under CWE-276 which describes improper privilege management, and aligns with ATT&CK technique T1068 which focuses on exploit for privilege escalation. The flaw stems from insufficient validation of access tokens and security descriptors within the CSC service implementation, allowing attackers to manipulate service behavior through crafted inputs.
The technical exploitation of CVE-2021-1655 occurs when a malicious user or process interacts with the CSC service in a manner that triggers the privilege escalation path. Attackers can leverage this vulnerability by creating specific conditions that cause the CSC service to execute code with elevated privileges. The service's handling of named pipes and inter-process communication creates a window where access controls can be bypassed, particularly when dealing with certain file system operations or registry access. The vulnerability manifests when the service fails to properly validate the security context of incoming requests, allowing unprivileged users to inject malicious code that executes with SYSTEM privileges. This occurs due to improper access control mechanisms within the service's security descriptor handling and token validation processes. The exploitation typically involves crafting specific service requests that cause the CSC service to perform operations with elevated privileges, effectively allowing attackers to execute arbitrary code with the highest system privileges. The underlying flaw demonstrates poor implementation of security checks that should normally prevent privilege escalation from occurring in the first place.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with complete system control capabilities. Once an attacker successfully exploits CVE-2021-1655, they gain the ability to install malware, modify system files, access all user data, and potentially establish persistence mechanisms within the compromised system. The vulnerability can be leveraged as a stepping stone for further attacks within a network environment, particularly in enterprise settings where lateral movement is common. Organizations that have not applied the relevant security patches face significant risk of complete system compromise, as the vulnerability allows attackers to bypass standard security controls. The impact is particularly severe in environments where users have local access to systems, as the exploit requires minimal privileges to initiate. This vulnerability can be particularly dangerous when combined with other exploits or when used in conjunction with social engineering attacks to gain initial access. The potential for data exfiltration, system disruption, and unauthorized access to sensitive information makes this a critical concern for all Windows-based environments. The vulnerability's impact is amplified in cloud environments and virtualized systems where the CSC service may be actively used for remote communication and file sharing operations.
Mitigation strategies for CVE-2021-1655 primarily focus on applying the official Microsoft security patches released to address the vulnerability. Organizations should prioritize immediate deployment of the relevant updates to prevent exploitation attempts. System administrators should also implement additional security measures including disabling unnecessary services, restricting user privileges, and monitoring for suspicious CSC service activity. Network segmentation and access control policies can help limit the potential impact if an attacker does manage to exploit the vulnerability. The implementation of security monitoring solutions that can detect anomalous behavior in CSC service operations provides an additional layer of protection. Regular vulnerability assessments and penetration testing should be conducted to identify potential exploitation attempts. Security teams should also consider implementing application whitelisting policies to prevent unauthorized executables from running with elevated privileges. The vulnerability highlights the importance of maintaining up-to-date systems and implementing comprehensive security monitoring. Organizations should also review their incident response procedures to ensure rapid detection and containment of potential exploitation attempts. Proper security awareness training for users can help prevent initial compromise through social engineering or other attack vectors that may be used to gain access to systems before exploiting this vulnerability.