Microsoft Windows Hyper-V NT Kernel Integration VSP Use-After-Free (CVE-2025-21334)

Historical catalog analysis: CISA added this entry on January 14, 2025. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. Check current vendor guidance before acting.

What the vulnerability is

CVE-2025-21334 is a use-after-free (CWE-416) vulnerability located within the Microsoft Windows Hyper-V NT Kernel Integration VSP. This flaw allows an attacker with local access to the system to escalate their privileges to the SYSTEM level.

Exposure and applicability

This vulnerability affects environments running Microsoft Windows that utilize the Hyper-V NT Kernel Integration VSP. Because this is a local privilege escalation (LPE) vulnerability, the primary exposure path requires the attacker to already have a foothold on the target system. The risk is most acute in multi-tenant or shared virtualization environments where restricting local user capabilities is critical to preventing full host or kernel compromise.

Remediation priorities

Based on our analysis, organizations should prioritize remediation based on the following hierarchy:

1. Patch Deployment: Apply the specific mitigations and updates provided by Microsoft via the Security Update Guide for CVE-2025-21334. This is the primary method for reducing exposure.
2. Asset Identification: Identify all Windows hosts where Hyper-V is active and the NT Kernel Integration VSP is in use to ensure no legacy or isolated systems are missed during the update cycle.
3. Product Decommissioning: In scenarios where vendor mitigations cannot be applied or are unavailable for a specific legacy version, the source suggests discontinuing use of the affected product.

How to validate remediation

To verify that exposure has been reduced, defenders should move beyond simple version checks. We recommend the following validation approach:

• Patch Verification: Confirm through centralized patch management logs that the specific update addressing CVE-2025-21334 has been successfully installed and initialized on all identified Hyper-V hosts.
• Configuration Audit: Verify that the system state reflects the application of vendor-recommended mitigations.

It is important to note that a version number check alone does not prove mitigation; verification must confirm that the patch was applied correctly and the system has been rebooted if required by the vendor to finalize the kernel-level update.

Limits and open questions

There are several unknowns regarding this vulnerability. It is currently unknown whether this flaw has been utilized in known ransomware campaigns. Additionally, while CISA has established a remediation deadline of February 4, 2025, for federal agencies, this date serves as a benchmark rather than a universal requirement for all private sector organizations. Residual risk remains if attackers develop methods to bypass the applied mitigations or if dependencies within the Hyper-V stack introduce secondary vectors.

Source and editorial note

CVE-2025-21334: Microsoft Windows Hyper-V NT Kernel Integration VSP Use-After-Free Vulnerability · Source date: January 14, 2025 · Retrieved August 31, 2026.

Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.

Archive date: January 17, 2025. The displayed post date is assigned three days after the source date to organize this retrospective archive; it does not mean this site published the analysis then. First published by this site: October 28, 2026 at 00:24 UTC.

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