CVE-2026-21247: Windows 10 1607 Hyper-V RCE Vulnerability

CVE-2026-21247 Overview

CVE-2026-21247 is an improper input validation vulnerability in Windows Hyper-V that allows an authorized attacker to execute code locally. This flaw exists within the Hyper-V virtualization platform component, where insufficient validation of user-supplied input can be leveraged to achieve local code execution on affected Windows systems.

Critical Impact

Successful exploitation of this vulnerability allows an authorized attacker with local access to execute arbitrary code on the host system, potentially compromising the confidentiality, integrity, and availability of the underlying virtualization infrastructure.

Affected Products

• Microsoft Windows 10 1607, 1809, 21H2, 22H2 (x64)
• Microsoft Windows 11 23H2, 24H2, 25H2 (x64 and ARM64)
• Microsoft Windows Server 2016, 2019, 2022, 2022 23H2, 2025

Discovery Timeline

• February 10, 2026 - CVE-2026-21247 published to NVD
• February 11, 2026 - Last updated in NVD database

Technical Details for CVE-2026-21247

Vulnerability Analysis

This vulnerability is classified under CWE-20 (Improper Input Validation), indicating that the Hyper-V component fails to properly validate or sanitize input before processing it. In virtualization environments, improper input validation is particularly dangerous as it can allow attackers to break out of expected execution boundaries. The vulnerability requires local access and an authorized user account, meaning the attacker must already have some level of access to the target system. Additionally, user interaction is required for successful exploitation, suggesting the attack may involve tricking a user into performing a specific action.

The local attack vector combined with the requirement for user interaction limits the scope of potential attacks but does not diminish the severity of the impact. Once successfully exploited, the attacker gains the ability to execute arbitrary code, which could lead to complete compromise of the affected system's confidentiality, integrity, and availability.

Root Cause

The root cause of CVE-2026-21247 is improper input validation within the Windows Hyper-V virtualization component. The Hyper-V subsystem fails to adequately validate certain inputs, allowing malformed or malicious data to be processed in unintended ways. This lack of proper boundary checking and input sanitization creates an avenue for code execution when specially crafted input is processed by the vulnerable component.

Attack Vector

The attack vector for this vulnerability is local, requiring the attacker to have authenticated access to the target system. The exploitation process involves:

1. An attacker gains local access to a Windows system with Hyper-V enabled
2. The attacker crafts malicious input designed to bypass validation checks
3. User interaction is required to trigger the vulnerable code path
4. When processed, the malformed input leads to code execution in the context of the Hyper-V process

The vulnerability does not change the scope of the attack, meaning any code execution remains within the same security boundary. However, the potential impact includes high confidentiality, integrity, and availability compromise on the affected system.

Detection Methods for CVE-2026-21247

Indicators of Compromise

• Unusual process activity originating from Hyper-V-related services or components (vmwp.exe, vmms.exe)
• Unexpected child processes spawned by Hyper-V worker processes
• Anomalous memory allocation patterns in Hyper-V virtualization processes
• Suspicious user activity requiring interaction with Hyper-V management interfaces

Detection Strategies

• Monitor Windows Event Logs for Hyper-V-related errors and unusual service behavior
• Implement endpoint detection rules to identify suspicious process chains involving Hyper-V components
• Deploy behavioral analysis to detect anomalous code execution patterns in virtualization contexts
• Utilize SentinelOne's Behavioral AI to identify exploitation attempts targeting input validation flaws

Monitoring Recommendations

• Enable verbose logging for Hyper-V Virtual Machine Management Service
• Monitor for unexpected modifications to Hyper-V configuration files and settings
• Track process creation events for Hyper-V-related executables
• Implement file integrity monitoring on critical Hyper-V binaries

How to Mitigate CVE-2026-21247

Immediate Actions Required

• Apply the latest Microsoft security updates as documented in the Microsoft Security Update Guide
• Review and restrict user permissions on systems with Hyper-V enabled
• Limit local access to Hyper-V hosts to only authorized administrators
• Implement the principle of least privilege for Hyper-V management

Patch Information

Microsoft has released security updates to address this vulnerability. Administrators should consult the Microsoft Security Update Guide for CVE-2026-21247 for specific patch information and update procedures applicable to their affected Windows versions.

Workarounds

• If Hyper-V is not required, disable the Hyper-V feature on affected systems
• Implement strict access controls to limit which users can interact with Hyper-V
• Consider network segmentation to isolate Hyper-V hosts from general network traffic
• Enforce security awareness training to reduce the likelihood of user interaction with malicious content

# Disable Hyper-V if not required (requires restart)
dism.exe /Online /Disable-Feature:Microsoft-Hyper-V-All

# Verify Hyper-V status
Get-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V