CVE-2026-20825: Windows Hyper-V Information Disclosure

CVE-2026-20825 Overview

CVE-2026-20825 is an improper access control vulnerability in Windows Hyper-V that allows an authorized attacker to disclose sensitive information locally. This vulnerability stems from CWE-284 (Improper Access Control), where the hypervisor fails to properly enforce access restrictions, potentially exposing confidential data to privileged local users.

Critical Impact

An attacker with high privileges on a Hyper-V host can exploit this vulnerability to access sensitive information that should be protected by the hypervisor's isolation boundaries, potentially compromising the confidentiality of virtualized environments.

Affected Products

• Windows Hyper-V
• Windows Server with Hyper-V role enabled
• Windows 10/11 with Hyper-V feature enabled

Discovery Timeline

• January 13, 2026 - CVE-2026-20825 published to NVD
• January 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20825

Vulnerability Analysis

This vulnerability represents an improper access control flaw within Windows Hyper-V, Microsoft's hardware virtualization platform. The issue allows a locally authenticated attacker with elevated privileges to bypass intended access restrictions and disclose sensitive information.

The attack requires local access to the target system and high privileges, limiting the exploitability to scenarios where an attacker has already established a foothold with administrative access. However, in multi-tenant virtualization environments, this could have significant implications for data confidentiality between virtual machines or between guest VMs and the host system.

The vulnerability specifically impacts the confidentiality of data within the Hyper-V environment. There is no direct impact on system integrity or availability, making this primarily an information disclosure issue.

Root Cause

The vulnerability originates from improper access control mechanisms (CWE-284) within Windows Hyper-V. The hypervisor fails to properly validate or enforce access restrictions, allowing privileged local users to access information that should be isolated and protected by the virtualization layer's security boundaries.

Attack Vector

Exploitation of CVE-2026-20825 requires local access to the affected system with high privileges. An attacker would need to:

1. Obtain local access to a Windows system running Hyper-V
2. Escalate or possess high-level privileges (administrator or equivalent)
3. Leverage the improper access control flaw to read sensitive data

The local attack vector and high privilege requirement reduce the likelihood of opportunistic exploitation but remain a concern in environments where privileged insiders or compromised administrator accounts pose a threat.

For detailed technical information about this vulnerability, refer to the Microsoft Security Advisory CVE-2026-20825.

Detection Methods for CVE-2026-20825

Indicators of Compromise

• Unusual access patterns to Hyper-V management interfaces by privileged accounts
• Unexpected queries or attempts to access virtual machine memory or configuration data
• Anomalous behavior from processes interacting with vmms.exe (Hyper-V Virtual Machine Management Service)

Detection Strategies

• Monitor Windows Security Event Logs for unusual Hyper-V management activities from privileged accounts
• Implement endpoint detection rules for abnormal access to Hyper-V components and virtual machine resources
• Deploy behavioral analysis to detect privileged users accessing data outside their normal operational scope

Monitoring Recommendations

• Enable detailed auditing for Hyper-V management operations and virtual machine access events
• Configure alerts for privileged account activity on Hyper-V hosts during non-standard hours
• Review access logs for the Hyper-V Virtual Machine Management Service regularly

How to Mitigate CVE-2026-20825

Immediate Actions Required

• Review and restrict administrative access to Hyper-V hosts to only essential personnel
• Audit current privileged account usage on systems with Hyper-V enabled
• Apply the latest security updates from Microsoft as they become available
• Implement the principle of least privilege for all accounts with access to Hyper-V systems

Patch Information

Microsoft has released security guidance for this vulnerability. Organizations should consult the Microsoft Security Advisory CVE-2026-20825 for patch availability and installation instructions. Apply the recommended security updates through Windows Update or WSUS as soon as they are available.

Workarounds

• Restrict network access to Hyper-V hosts to limit potential attack entry points
• Implement just-in-time (JIT) access for administrative privileges on Hyper-V systems
• Enable Credential Guard and other virtualization-based security features where applicable
• Segment Hyper-V management networks from general corporate networks

# Example: Audit Hyper-V administrative access using PowerShell
Get-LocalGroupMember -Group "Hyper-V Administrators"
# Review and remove unnecessary accounts from the Hyper-V Administrators group