CVE-2026-45641: Windows Hyper-V Type Confusion Remote Code Execution Vulnerability

Technical summary

The vulnerability involves improper type handling in Windows Hyper-V (CWE-125: Out-of-bounds Read; CWE-843: Access of Resource Using Incompatible Type). When the hypervisor processes resource access requests, it fails to validate type compatibility, allowing an attacker to read from or write to memory regions using an incorrect type interpretation. This type confusion enables an attacker to corrupt hypervisor data structures or escape the bounds of allocated buffers, ultimately achieving code execution in the hypervisor context. The attack requires local code execution capability but no user interaction or elevated privileges to trigger.

Business impact

This vulnerability poses a critical risk to organizations running Hyper-V environments. An attacker with any local code execution capability—whether through a previously patched vulnerability, social engineering, or legitimate system access—can escalate to full control of the hypervisor and all guest virtual machines. This breaks isolation guarantees and puts multi-tenant cloud deployments, containerized workloads, and virtual infrastructure at severe risk. Compromised hypervisors can facilitate lateral movement, persistent backdoors, and wholesale data exfiltration from hosted systems.

Affected systems

The vulnerability affects Windows 10 versions 21H2 and 22H2, Windows 11 versions 23H2, 24H2, 25H2, and 26H1, Windows Server 2022, and Windows Server 2025. Any system with Hyper-V enabled—including client operating systems used for development or testing—is potentially affected. Organizations should audit their environment for these specific builds and versions.

Exploitability

The attack vector is local (AV:L) with low attack complexity (AC:L), requiring no user interaction (UI:N) or special privileges (PR:N). An attacker who has achieved local code execution on a Hyper-V host can immediately exploit this flaw without additional steps or user assistance. While the initial foothold requires local access, the impact is severe: complete compromise of the hypervisor with high confidentiality, integrity, and availability impact (C:H/I:H/A:H). The CVSS 3.1 score of 8.4 reflects the combination of easy exploitation and catastrophic impact.

Remediation

Microsoft patches for this vulnerability should be applied immediately to all affected systems. Administrators must prioritize Hyper-V hosts and servers in patch deployment schedules. For systems where patching must be delayed, restrict local code execution opportunities by hardening the host OS, limiting user access, and disabling unnecessary services. Consider network isolation or enhanced monitoring of Hyper-V traffic as interim measures. Verify the patch is applied by checking Windows Update history or using the Security Update Guide reference provided by Microsoft.

Patch guidance

Obtain the latest cumulative security update from Microsoft that addresses CVE-2026-45641 (verify against the Microsoft Security Update Guide for the specific KB articles for your Windows version). Install updates for all affected versions: Windows 10 21H2/22H2, Windows 11 23H2/24H2/25H2/26H1, Windows Server 2022, and Windows Server 2025. Test updates in a non-production Hyper-V environment first to ensure compatibility with your guest VMs and workloads. Schedule patching during maintenance windows when guest VM availability can be temporarily impacted. After patching, confirm version numbers match the advisory recommendations.

Detection guidance

Monitor Windows Event Viewer for unusual Hyper-V-related errors or crashes, particularly in the System and Hyper-V logs. Look for unexpected code execution within hypervisor context or suspicious type confusion errors. Enable Windows Defender Application Control (WDAC) policies on Hyper-V hosts to block unauthorized code execution. Intrusion detection systems should alert on memory corruption indicators on virtualization hosts. Organizations with EDR deployed on the host OS should tune detection for local privilege escalation patterns. Implement file integrity monitoring on hypervisor binaries to detect post-exploitation persistence attempts.

Why prioritize this

This vulnerability merits immediate patching attention due to its combination of high CVSS score (8.4), unrestricted local exploitability, and devastating impact on virtualized infrastructure. Unlike guest OS vulnerabilities, a compromised hypervisor affects all downstream VMs and workloads. The broad version coverage (spanning Windows 10, Windows 11, and Windows Server 2022–2025) means most enterprise environments with Hyper-V deployments require urgent remediation. Organizations operating multi-tenant cloud infrastructure should treat this as a critical security incident requiring expedited patch deployment.

Risk score, explained

The CVSS 3.1 score of 8.4 (HIGH severity) reflects: (1) Local attack vector with no complexity, executable by any local process; (2) Complete compromise of the system with high impact across confidentiality, integrity, and availability; (3) The type confusion flaw is straightforward to trigger once local code execution is achieved; (4) The scope is unchanged (hypervisor compromise does not escape to other systems directly, but enables control of all guest VMs). The score stops short of 9.0+ because it requires prior local code execution, but the impact is severe enough to demand top-tier response.

Frequently asked questions