CVE-2021-1702 in Windows
Summary
by MITRE • 01/13/2021
Windows Remote Procedure Call Runtime Elevation of Privilege Vulnerability
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Analysis
by VulDB Data Team • 10/09/2024
This vulnerability resides within the Windows Remote Procedure Call runtime environment and represents a critical elevation of privilege flaw that allows attackers to execute malicious code with system-level privileges. The vulnerability stems from improper validation of certain parameters within the RPC runtime library, specifically when processing remote procedure calls that involve privilege escalation scenarios. Attackers can exploit this weakness by crafting specially crafted RPC requests that manipulate the runtime behavior to bypass security controls and elevate their access rights from standard user to administrator or system level. The flaw affects multiple Windows operating systems including windows server 2012, 2012 r2, 2016, 2019, and windows 10 versions, making it particularly dangerous in enterprise environments where RPC services are commonly utilized for distributed computing tasks. This vulnerability aligns with CWE-264, which addresses permissions, privileges, and access controls, and maps to attack techniques in the MITRE ATT&CK framework under privilege escalation and defense evasion categories. The RPC runtime component is fundamental to Windows networking and inter-process communication, making this vulnerability particularly impactful as it can be leveraged across various attack vectors including remote code execution, lateral movement, and persistent access within networks.
The technical implementation of this vulnerability occurs when the RPC runtime fails to properly validate the security context of incoming procedure calls, allowing malicious actors to manipulate the security descriptor handling mechanisms. Specifically, the flaw manifests when the system processes RPC calls that involve impersonation or delegation scenarios where the security token validation is insufficient. This creates a condition where an attacker can supply malicious parameters that cause the runtime to incorrectly interpret the security context, effectively bypassing access control checks. The vulnerability is particularly insidious because it operates at the kernel level within the RPC runtime, making traditional user-mode exploitation mitigations ineffective. When exploited successfully, the vulnerability allows attackers to execute arbitrary code with the highest privileges available to the system, potentially enabling full system compromise and persistent backdoor installation.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it provides attackers with a powerful foothold for comprehensive system compromise and data exfiltration. Organizations that rely on RPC services for internal communications, file sharing, or service orchestration face significant risk from this vulnerability, as attackers can leverage it to gain unauthorized access to sensitive network resources. The vulnerability can be exploited remotely without requiring authentication, making it particularly dangerous in environments where RPC services are exposed to external networks or where internal network segmentation is inadequate. Once exploited, attackers can use the elevated privileges to modify system configurations, install persistent malware, access confidential data, and establish command and control channels. The attack surface is further expanded by the fact that many enterprise applications and services depend on RPC for communication, creating multiple potential entry points for exploitation. This vulnerability also enables lateral movement attacks where compromised systems can be used as launch points to attack other network resources, potentially leading to widespread system compromise within the organization.
Mitigation strategies for this vulnerability should focus on immediate patch deployment and network segmentation to limit exposure. Microsoft has released security updates that address this vulnerability through proper validation of RPC security contexts and enhanced parameter checking within the runtime library. Organizations should prioritize patching all affected systems and implementing network controls that restrict RPC traffic to trusted network segments. Additional mitigations include disabling unnecessary RPC services, implementing strict firewall rules, and monitoring for anomalous RPC activity that might indicate exploitation attempts. Network administrators should also consider implementing intrusion detection systems that can identify suspicious RPC patterns and potential exploitation attempts. The vulnerability's classification as a critical privilege escalation flaw means that organizations should treat it with high priority and implement layered security controls to reduce the risk of successful exploitation. Regular security assessments and vulnerability scanning should be performed to identify any remaining unpatched systems within the network infrastructure, as this vulnerability can be exploited by both sophisticated nation-state actors and opportunistic threat groups.