CVE-2026-69910: Windows Hyper-V Buffer Overflow Vulnerability

CVE-2026-69910 Overview

CVE-2026-69910 is a stack-based buffer overflow [CWE-121] in Windows Hyper-V. An unauthorized attacker can execute code over a network without prior authentication or user interaction. Microsoft published the advisory through the Microsoft Security Response Center (MSRC).

The flaw carries a CVSS 3.1 base score of 9.8. Successful exploitation compromises confidentiality, integrity, and availability of the affected hypervisor host. Because Hyper-V mediates virtualization workloads, code execution at the hypervisor layer places all hosted virtual machines at risk.

Critical Impact
Network-reachable Hyper-V hosts can be compromised by an unauthenticated remote attacker, enabling arbitrary code execution on the virtualization host.

Affected Products

Microsoft Windows Hyper-V (see the Microsoft advisory for the current list of affected builds)
Windows Server editions with the Hyper-V role enabled
Windows client editions shipping the Hyper-V feature

Discovery Timeline

2026-09-08 - CVE-2026-69910 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-69910

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow within the Windows Hyper-V component. Hyper-V processes untrusted input from network-adjacent sources without adequate bounds validation on a stack buffer. An attacker who can reach the vulnerable code path can overwrite adjacent stack memory, including saved return addresses and control-flow structures.

Exploitation does not require authentication, user interaction, or elevated privileges. The attack vector is network-based with low attack complexity. The EPSS score is 0.996% with a percentile near 60.63, indicating meaningful predicted exploitation probability relative to the broader CVE population.

Successful exploitation yields arbitrary code execution in the security context of the vulnerable Hyper-V process. Because Hyper-V runs with high privilege on the host, attackers can pivot from the network into the hypervisor and, from there, into guest workloads.

Root Cause

The root cause is improper bounds checking on data written to a fixed-size stack buffer in Hyper-V. This condition maps to CWE-121 (Stack-based Buffer Overflow). Microsoft has not published component-level source detail beyond the MSRC advisory.

Attack Vector

An unauthenticated remote attacker sends crafted network traffic to a service exposed by the Hyper-V role. The malformed input overflows the stack buffer during parsing. The attacker leverages the overflow to hijack execution and run code on the host. Refer to the Microsoft Vulnerability CVE-2026-69910 advisory for protocol-specific detail as Microsoft releases it.

No verified public proof-of-concept is available at the time of writing. No exploitation in the wild has been confirmed.

Detection Methods for CVE-2026-69910

Indicators of Compromise

Unexpected crashes or restarts of Hyper-V host services (vmms.exe, vmwp.exe) correlated with inbound network activity.
New or unusual child processes spawned by Hyper-V worker processes on the host.
Anomalous outbound connections originating from the Hyper-V host immediately after inbound sessions to virtualization services.

Detection Strategies

Monitor Windows Event Logs for Hyper-V-Worker and Hyper-V-VMMS error, warning, and crash events during and after suspicious network traffic.
Alert on process-creation events where vmms.exe or vmwp.exe spawns interpreters or LOLBins such as cmd.exe, powershell.exe, or rundll32.exe.
Inspect network flows for malformed or oversized packets directed at Hyper-V-managed ports and protocols exposed on host interfaces.

Monitoring Recommendations

Baseline normal Hyper-V process behavior and file-integrity state, then alert on deviations.
Forward Windows security, system, and Hyper-V operational logs to a centralized SIEM for correlation across hosts.
Enable EDR telemetry on all Hyper-V hosts to capture in-memory activity and stack anomalies indicative of overflow exploitation.

How to Mitigate CVE-2026-69910

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-69910 to all Windows Server and Windows client systems running Hyper-V.
Inventory all systems with the Hyper-V role enabled and prioritize internet-adjacent or DMZ hosts for immediate patching.
Restrict network access to Hyper-V management and virtualization services using host firewalls and network segmentation.

Patch Information

Microsoft has published guidance and updates through the Microsoft Security Response Center. Administrators should consult the Microsoft Vulnerability CVE-2026-69910 advisory for the applicable KB numbers, affected build ranges, and update rollups. Apply patches through Windows Update, WSUS, or your endpoint management tooling.

Workarounds

Disable the Hyper-V role on systems that do not require virtualization until patches are applied.
Block untrusted network access to Hyper-V-related ports at perimeter and internal firewalls.
Isolate Hyper-V management traffic on a dedicated management VLAN separated from general user networks.

bash

# Verify Hyper-V role status and disable if unused (PowerShell, run as Administrator)
Get-WindowsFeature -Name Hyper-V
Disable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V-All

# Restrict inbound access to Hyper-V management from an admin subnet only
New-NetFirewallRule -DisplayName "Restrict Hyper-V Mgmt" -Direction Inbound `
  -Program "%SystemRoot%\System32\vmms.exe" -Action Block -Profile Any