CVE-2021-26416 in Windows
Summary
by MITRE • 04/14/2021
Windows Hyper-V Denial of Service Vulnerability
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Analysis
by VulDB Data Team • 04/17/2021
The Windows Hyper-V Denial of Service vulnerability identified as CVE-2021-26416 represents a critical security flaw within Microsoft's virtualization platform that affects systems running Hyper-V hypervisor. This vulnerability specifically targets the memory management subsystem of Hyper-V, creating a condition where malicious actors can exploit improper input validation mechanisms to trigger system instability and service disruption. The flaw exists in the way Hyper-V processes certain memory allocation requests within the virtual machine management interfaces, allowing unauthorized users to craft specific inputs that cause the hypervisor to crash or become unresponsive. According to the Common Weakness Enumeration catalog, this vulnerability maps to CWE-129, which describes improper validation of input ranges, as the system fails to properly validate memory allocation parameters before processing them. The issue particularly affects systems where Hyper-V is enabled and running, including both server and client operating systems that support virtualization features.
The technical exploitation of CVE-2021-26416 occurs when an attacker crafts malicious memory allocation requests that bypass normal validation checks within the Hyper-V memory manager. The vulnerability manifests when the hypervisor receives malformed memory descriptors or allocation parameters that cause it to enter an inconsistent state during memory management operations. This flaw can be triggered through various attack vectors including remote code execution scenarios or local privilege escalation attempts where an attacker has access to the system. The vulnerability demonstrates characteristics consistent with the ATT&CK framework's privilege escalation techniques, particularly in how it leverages hypervisor-level memory management functions to achieve system instability. The memory management subsystem in Hyper-V relies on complex data structures and allocation algorithms that, when fed with malformed inputs, can cause memory corruption or resource exhaustion conditions that ultimately result in denial of service.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire virtualized environments and the availability of critical business applications. Organizations running Hyper-V environments are particularly vulnerable as the flaw affects the core hypervisor functionality that manages all virtual machine operations, potentially causing cascading failures across multiple virtual machines hosted on the same physical system. When exploited successfully, the vulnerability can lead to complete system crashes requiring manual intervention and system restarts, resulting in significant downtime and potential data loss. The impact is amplified in cloud environments and data centers where Hyper-V serves as the foundation for virtualized infrastructure, potentially affecting numerous tenants or customers simultaneously. According to Microsoft security advisories, systems with multiple virtual machines running on a compromised Hyper-V host may experience complete service outages, making this vulnerability particularly dangerous for enterprise environments. The vulnerability's exploitation requires minimal privileges in many scenarios, making it accessible to a wide range of threat actors from casual attackers to sophisticated adversaries.
Mitigation strategies for CVE-2021-26416 focus on both immediate patching and operational security measures to reduce the attack surface and prevent exploitation. Microsoft released security updates in their regular monthly patches that address the memory validation issues within Hyper-V's memory management subsystem, requiring organizations to apply the appropriate updates to their systems. The recommended approach includes implementing network segmentation to limit access to Hyper-V management interfaces and disabling Hyper-V functionality on systems where it is not required. Organizations should also implement monitoring solutions that can detect anomalous memory allocation patterns or system instability that may indicate exploitation attempts. Additional defensive measures include configuring virtual machine resource limits to prevent single malicious VM from consuming excessive resources and implementing proper access controls to restrict who can manage Hyper-V configurations. Security teams should also consider deploying intrusion detection systems that can monitor for known exploit patterns targeting Hyper-V memory management functions, as the vulnerability's exploitation patterns are well-documented and can be detected through behavioral analysis. The vulnerability's classification as a denial of service issue means that traditional antivirus solutions may not detect the exploitation, requiring specialized monitoring and response procedures to effectively protect against this specific threat.