CVE-2025-55328 Overview
CVE-2025-55328 is an elevation of privilege vulnerability in Windows Hyper-V. The flaw stems from concurrent execution using a shared resource with improper synchronization, commonly known as a race condition [CWE-362]. An authorized local attacker can exploit this weakness to elevate privileges on the affected host.
Microsoft published the advisory on October 14, 2025. The vulnerability affects a broad range of Windows client and server releases that ship the Hyper-V role, from Windows 10 1507 through Windows 11 25H2 and Windows Server 2016 through Windows Server 2025.
Critical Impact
Successful exploitation grants an attacker high impact on confidentiality, integrity, and availability of the Hyper-V host, enabling privilege escalation from a low-privileged local context.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (22H2, 23H2, 24H2, 25H2)
- Microsoft Windows Server 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-10-14 - Microsoft publishes the security advisory for CVE-2025-55328
- 2025-10-14 - CVE-2025-55328 published to the National Vulnerability Database
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-55328
Vulnerability Analysis
Hyper-V is the Windows type-1 hypervisor that partitions physical hardware for virtual machines. It relies on several coordinating components, including the Virtual Machine Management Service (vmms.exe), the worker process (vmwp.exe), and kernel-mode drivers such as hvix64.exe and vid.sys. These components share state across privilege boundaries and virtualization contexts.
The vulnerability arises when two or more concurrent execution paths access a shared resource without correct synchronization. An attacker with local, low-privileged access can time operations to interleave with a privileged Hyper-V code path. Winning the race allows the attacker to manipulate the shared state before proper validation completes.
Exploitation requires high attack complexity, reflecting the timing precision needed to trigger the race window reliably. When successful, the outcome is privilege elevation on the host with full impact on confidentiality, integrity, and availability.
Root Cause
The root cause is improper synchronization of a shared resource within Hyper-V, classified under [CWE-362]. A time-of-check to time-of-use style flaw allows attacker-controlled data or handles to change between validation and consumption by a privileged component.
Attack Vector
The attack vector is local. An authenticated attacker running code on a Hyper-V enabled host executes a specially crafted workload that repeatedly invokes the vulnerable code path. By tuning thread priorities, processor affinity, and I/O timing, the attacker aligns their operations with the privileged handler to win the race and gain elevated privileges. No user interaction is required.
Microsoft has not released technical exploitation details. See the Microsoft Security Update Guide for CVE-2025-55328 for vendor guidance.
Detection Methods for CVE-2025-55328
Indicators of Compromise
- Unexpected creation of privileged processes as child processes of vmwp.exe or vmms.exe
- Anomalous handle duplication or token manipulation events originating from non-administrative user contexts on Hyper-V hosts
- Repeated, tight-loop invocation of Hyper-V APIs or IOCTLs from unusual, low-privileged processes
Detection Strategies
- Baseline normal Hyper-V worker and management process behavior, then alert on deviations such as unusual child processes or token elevations
- Correlate high-frequency virtualization syscalls from a single non-admin user with subsequent privilege changes on the same host
- Monitor Windows Event Log channels Microsoft-Windows-Hyper-V-* for unusual error patterns or repeated failures that may indicate race attempts
Monitoring Recommendations
- Enable Windows Defender Application Control and audit-mode logging on Hyper-V hosts to record unexpected binary execution
- Forward Sysmon process creation, image load, and handle events from Hyper-V hosts to a centralized analytics platform for behavioral analysis
- Track patch compliance across all Hyper-V enabled Windows 10, Windows 11, and Windows Server systems to identify unpatched hosts
How to Mitigate CVE-2025-55328
Immediate Actions Required
- Apply the October 2025 Microsoft security updates for CVE-2025-55328 to all Hyper-V enabled hosts
- Inventory Windows systems with the Hyper-V role or Hyper-V Platform feature enabled and prioritize them for patching
- Restrict interactive and remote logon rights on Hyper-V hosts to a minimal set of administrators
Patch Information
Microsoft has issued security updates addressing CVE-2025-55328 across all supported Windows client and server versions listed in the advisory. Refer to the Microsoft Security Update Guide for CVE-2025-55328 for the specific KB articles applicable to each affected build.
Workarounds
- Where feasible, disable the Hyper-V role on hosts that do not require virtualization until patches are applied
- Enforce least-privilege access controls to prevent untrusted users from obtaining local logon on virtualization hosts
- Segregate Hyper-V management hosts from general-purpose user workloads to reduce local attack surface
# 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
# Optionally disable the Hyper-V role on systems that do not require it
Disable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V-All
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
