CVE-2025-27491 Overview
CVE-2025-27491 is a use-after-free vulnerability [CWE-416] in Windows Hyper-V that allows an authorized attacker to execute code over a network. Microsoft assigned this issue a CVSS score of 7.1 and published the advisory on April 8, 2025. The flaw affects a broad range of Windows client and server platforms running the Hyper-V role, including Windows 10, Windows 11, and Windows Server 2016 through 2025. Successful exploitation requires user interaction and authenticated access, but yields high impact on confidentiality, integrity, and availability of the targeted host.
Critical Impact
Authorized attackers can trigger memory corruption in Hyper-V over the network to execute arbitrary code, potentially escaping virtualization boundaries and compromising the underlying host.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (22H2, 23H2, 24H2)
- Microsoft Windows Server 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-04-08 - CVE-2025-27491 published to NVD by Microsoft
- 2025-07-08 - Last updated in NVD database
Technical Details for CVE-2025-27491
Vulnerability Analysis
The vulnerability resides in the Windows Hyper-V hypervisor component, which provides hardware virtualization for Windows clients and servers. Hyper-V exposes virtualization services to guests and management interfaces over the network. A use-after-free condition in this component permits an authorized attacker to reference memory after it has been released. When triggered, the dangling reference operates on attacker-influenced data, enabling arbitrary code execution on the host. The attack vector is network-based, but exploitation complexity is high and requires user interaction, narrowing the feasible exploitation window.
Root Cause
The root cause is improper object lifetime management within Hyper-V [CWE-416]. A code path releases a kernel object while another path retains a reference to it. Subsequent operations dereference the freed memory, which an attacker can groom to contain controlled data structures. This corruption of kernel memory enables hijacking of control flow within the hypervisor or its virtualization stack.
Attack Vector
An authorized attacker on the network sends crafted requests to a Hyper-V host and induces a victim to perform an action that triggers the vulnerable code path. The flaw is exploitable from a guest virtual machine or from another network-reachable principal with valid credentials. Successful exploitation breaches the isolation boundary that Hyper-V provides between guests and the host, compromising any virtual machine running on the affected system. No public proof-of-concept exploit is currently available, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog.
For technical details, refer to the Microsoft CVE-2025-27491 Advisory.
Detection Methods for CVE-2025-27491
Indicators of Compromise
- Unexpected Hyper-V service crashes, bug checks, or restarts on hosts running the Hyper-V role.
- Anomalous authenticated network connections to Hyper-V management ports from guest VMs or unusual sources.
- Kernel-mode crash dumps referencing vmms.exe, vmwp.exe, or Hyper-V virtualization stack components.
Detection Strategies
- Monitor Windows Event Logs for Hyper-V-Hypervisor, Hyper-V-VMMS, and Hyper-V-Worker channel errors indicating abnormal worker process termination.
- Correlate guest-to-host network activity with subsequent host instability events to identify attempted exploitation patterns.
- Apply behavioral identification on the Hyper-V host for unexpected child process creation by vmwp.exe or vmms.exe.
Monitoring Recommendations
- Track patch compliance state across all Windows hosts with the Hyper-V role enabled.
- Audit privileged account usage capable of authenticating against Hyper-V management interfaces.
- Forward Hyper-V operational logs and host kernel telemetry to a centralized analytics platform for long-term retention and correlation.
How to Mitigate CVE-2025-27491
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2025-27491 Advisory to all affected Windows and Windows Server systems running Hyper-V.
- Prioritize patching on hosts that run multi-tenant workloads or expose Hyper-V services to less-trusted networks.
- Restrict authenticated access to Hyper-V management endpoints to administrative networks only.
Patch Information
Microsoft released a security update addressing CVE-2025-27491 as part of its April 2025 Patch Tuesday cycle. Administrators should consult the Microsoft CVE-2025-27491 Advisory for the specific KB articles applicable to each Windows version, including Windows 10, Windows 11, and Windows Server 2016 through 2025.
Workarounds
- Disable the Hyper-V role on systems that do not require virtualization until patches are deployed.
- Enforce network segmentation between guest virtual machines and Hyper-V management interfaces.
- Require multi-factor authentication for all accounts permitted to interact with Hyper-V administrative services.
# Verify Hyper-V role status and installed updates on a Windows host
Get-WindowsFeature -Name Hyper-V
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
