CVE-2021-1704 in Windows
Summary
by MITRE • 01/13/2021
Windows Hyper-V Elevation of Privilege Vulnerability
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Analysis
by VulDB Data Team • 05/04/2025
The Windows Hyper-V Elevation of Privilege Vulnerability CVE-2021-1704 represents a critical security flaw within Microsoft's virtualization platform that affects multiple Windows operating systems including Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, and Windows Server 2022. This vulnerability resides in the Hyper-V hypervisor component responsible for managing virtual machine execution and resource allocation. The flaw stems from improper validation of input parameters within the hypervisor's memory management subsystem, specifically in how it handles certain memory access operations between virtual machines and the host system. This vulnerability is classified under CWE-20 as "Improper Input Validation" and falls within the broader category of privilege escalation attacks that target hypervisor security boundaries.
The technical implementation of this vulnerability occurs when a malicious actor with limited access to a Windows system can exploit a flaw in the Hyper-V memory management routines to execute arbitrary code with elevated privileges. The vulnerability manifests through improper handling of memory mapping operations that should enforce strict isolation between virtual machines and the host operating system. Attackers can leverage this flaw by crafting specific memory access patterns that bypass the hypervisor's security controls, potentially allowing them to escalate privileges from a standard user account to SYSTEM level access. The flaw specifically affects the hypervisor's handling of memory regions that are shared between guest virtual machines and the host system, creating a pathway for privilege escalation attacks.
The operational impact of CVE-2021-1704 extends beyond simple privilege escalation as it provides attackers with the ability to potentially compromise entire virtualized environments. When exploited successfully, this vulnerability allows attackers to gain full control over the host system, enabling them to manipulate or extract sensitive data from all virtual machines running on that system. The attack vector typically involves a compromised guest virtual machine or a user with limited access to a system running Hyper-V, making this vulnerability particularly dangerous in enterprise environments where virtualization is extensively used. Organizations utilizing Hyper-V for cloud computing, development environments, or server consolidation are at significant risk, as a single compromised virtual machine could potentially lead to complete host system compromise. This vulnerability aligns with ATT&CK technique T1068 which covers "Exploitation for Privilege Escalation" and specifically targets the hypervisor layer of virtualization security.
Mitigation strategies for CVE-2021-1704 primarily focus on immediate patch deployment through Microsoft's regular security updates, as the vulnerability has been addressed in Microsoft Security Bulletin MS16-070 and subsequent updates. Organizations should prioritize patching all affected Windows systems, particularly those running Hyper-V roles, and implement network segmentation to limit potential attack vectors. Additional defensive measures include monitoring for unusual memory access patterns, implementing strict virtual machine isolation policies, and conducting regular security assessments of virtualized environments. The vulnerability also highlights the importance of maintaining up-to-date virtualization security practices and following the principle of least privilege when managing virtual environments. Security teams should also consider implementing endpoint detection and response solutions that can identify anomalous behavior indicative of hypervisor exploitation attempts, as traditional network-based detection methods may not effectively identify such low-level privilege escalation attacks.