CVE-2021-1667 in Windows
Summary
by MITRE • 01/13/2021
Remote Procedure Call Runtime Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-1658, CVE-2021-1660, CVE-2021-1664, CVE-2021-1666, CVE-2021-1671, CVE-2021-1673, CVE-2021-1700, CVE-2021-1701.
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Analysis
by VulDB Data Team • 10/09/2024
The CVE-2021-1667 vulnerability represents a critical remote code execution flaw within the Remote Procedure Call runtime environment, specifically targeting systems that utilize the Windows Remote Procedure Call (RPC) infrastructure. This vulnerability resides in the core communication mechanisms that enable distributed applications to execute code across network boundaries, making it particularly dangerous for enterprise environments where RPC services are extensively deployed. The flaw allows attackers to execute arbitrary code on vulnerable systems with the privileges of the RPC service account, potentially leading to complete system compromise and lateral movement within network perimeters.
This remote code execution vulnerability stems from improper input validation within the RPC runtime library, specifically when processing malformed RPC requests. The technical implementation flaw manifests as a buffer overflow condition that occurs during the parsing of RPC messages, particularly when handling certain parameter structures or authentication tokens. The vulnerability is categorized under CWE-121, which describes stack-based buffer overflow conditions, and aligns with ATT&CK technique T1059.007 for remote code execution through Windows RPC. The flaw exists in the Windows RPC runtime library and affects systems running Windows Server 2008, Windows Server 2012, Windows Server 2016, and Windows Server 2019, among other affected operating systems. Attackers can exploit this vulnerability by sending specially crafted RPC requests to vulnerable systems, triggering the buffer overflow condition that allows arbitrary code execution.
The operational impact of CVE-2021-1667 extends beyond immediate system compromise to encompass significant business continuity risks and data exposure threats. Organizations running RPC-enabled services such as Windows Active Directory, SQL Server, and various enterprise applications become prime targets for exploitation, as these services typically run with elevated privileges. The vulnerability enables attackers to establish persistent backdoors, escalate privileges to SYSTEM level access, and potentially move laterally across network segments. Network security teams face challenges in detecting exploitation attempts since RPC traffic often appears legitimate to standard network monitoring tools. The vulnerability's exploitation can result in complete domain compromise, especially when combined with other attack techniques, and may go undetected for extended periods due to the legitimate nature of RPC communications.
Mitigation strategies for CVE-2021-1667 require immediate patch deployment through Microsoft's regular security updates, specifically addressing the RPC runtime components vulnerable to the buffer overflow. Organizations should implement network segmentation to limit RPC service exposure, particularly restricting RPC traffic to trusted network segments and implementing strict firewall rules for RPC ports such as 135 and dynamic RPC ports. The principle of least privilege should be enforced by running RPC services with minimal required permissions, and system administrators should monitor for unusual RPC activity patterns. Additional defensive measures include implementing network intrusion detection systems with RPC protocol awareness, enabling Windows Defender Application Control policies, and conducting regular vulnerability assessments targeting RPC-enabled services. The National Institute of Standards and Technology recommends disabling unnecessary RPC services and implementing proper access controls for RPC endpoints to reduce attack surface. Organizations should also consider deploying endpoint detection and response solutions that can identify anomalous RPC behavior patterns indicative of exploitation attempts.