CVE-2021-1691 in Windows
Summary
by MITRE • 01/13/2021
Hyper-V Denial of Service Vulnerability This CVE ID is unique from CVE-2021-1692.
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Analysis
by VulDB Data Team • 10/09/2024
The Hyper-V Denial of Service Vulnerability identified as CVE-2021-1691 represents a critical security flaw within Microsoft's virtualization platform that affects systems running Hyper-V hypervisors. This vulnerability specifically targets the virtual machine management components and can be exploited to cause system instability or complete service disruption. The flaw exists in the way Hyper-V handles certain memory management operations during virtual machine lifecycle events, creating an avenue for malicious actors to trigger system-wide denial of service conditions. The vulnerability is particularly concerning because it operates at the hypervisor level, meaning that successful exploitation could impact multiple virtual machines running on the same host system simultaneously. This type of vulnerability falls under the broader category of infrastructure security flaws that can have cascading effects across entire virtualized environments.
The technical implementation of this vulnerability stems from improper validation of memory allocation requests within the Hyper-V kernel-mode components. When a malicious user or process submits crafted memory management requests to the hypervisor, the system fails to properly validate the input parameters, leading to potential memory corruption or resource exhaustion conditions. The flaw is categorized as a CWE-125 vulnerability, which represents out-of-bounds read conditions that can occur when the system attempts to access memory locations beyond the allocated boundaries. This specific implementation issue allows attackers to manipulate the virtual machine memory management subsystem in ways that were not anticipated during the original design phase. The vulnerability can be triggered through various means including direct hypervisor API calls or through compromised virtual machine workloads that attempt to perform malicious memory operations.
The operational impact of CVE-2021-1691 extends beyond simple service disruption to encompass potential data integrity concerns and system availability risks within enterprise virtualized environments. Organizations running Hyper-V infrastructure are particularly vulnerable since this flaw affects the core hypervisor functionality that manages all virtual machine operations. When exploited, the vulnerability can cause virtual machines to crash, restart unexpectedly, or become unresponsive, leading to significant business disruption. The impact is amplified in cloud environments where multiple customers share the same physical infrastructure, as a single exploited vulnerability could potentially affect numerous virtual machines across different tenants. This vulnerability aligns with ATT&CK technique T1499 which describes resource hijacking through denial of service attacks, making it a particularly dangerous vector for attackers seeking to disrupt services or create cover for other malicious activities.
Mitigation strategies for CVE-2021-1691 should focus on immediate patch deployment from Microsoft, as the vendor has released security updates specifically addressing this vulnerability. Organizations must ensure that all Hyper-V hosts receive the applicable security patches as soon as possible, with particular attention to virtualization management systems that may be running older versions of Windows Server. Network segmentation and monitoring should be enhanced to detect unusual memory management patterns that might indicate exploitation attempts. The implementation of principle of least privilege for Hyper-V management interfaces can help reduce the attack surface, while regular vulnerability assessments should be conducted to identify any potential exploitation indicators. Additionally, organizations should consider implementing automated monitoring solutions that can detect abnormal virtual machine behavior patterns, as these may serve as early warning signs of exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date virtualization infrastructure and highlights the need for comprehensive security testing of hypervisor components to prevent similar issues from arising in the future.