CVE-2025-21333: Microsoft Windows Hyper-V NT Kernel Integration VSP Heap-based Buffer Overflow Vulnerability

What it is

Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability

Exploitation evidence

First exploit evidence seen: 2025-01-14 (earliest date across the sources below).

Exploited in the wild

• CISA KEV: listed since 2025-01-14. Source

Public exploit code

Exploit-DB

• EDB-52436: Microsoft Windows Server 2025 Hyper-V NT Kernel Integration VSP - Elevation of Privilege (2025-09-16)

GitHub proof-of-concept repositories

4 public repositories from 4 accounts, first seen 2025-02-27. Most starred: MrAle98/CVE-2025-21333-POC (232 stars), view repository.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: CISA KEV · Exploit-DB (OffSec) · nomi-sec/PoC-in-GitHub.

How to fix it

CISA required action

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. (source: CISA KEV)

Fixed versions

• microsoft windows 10 21h2: upgrade to 10.0.19044.5371 or later
• microsoft windows 10 22h2: upgrade to 10.0.19045.5371 or later
• microsoft windows 11 22h2: upgrade to 10.0.22621.4751 or later
• microsoft windows 11 23h2: upgrade to 10.0.22631.4751 or later
• microsoft windows 11 24h2: upgrade to 10.0.26100.2894 or later
• microsoft windows server 2022 23h2: upgrade to 10.0.25398.1369 or later
• microsoft windows server 2025: upgrade to 10.0.26100.2894 or later

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

• https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2025-21333 (CISA KEV notes)
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21333 (Patch, Vendor Advisory)
• https://www.vicarius.io/vsociety/posts/cve-2025-21333-elevated-privilege-exposure-in-windows-hyper-v-by-microsoft-detection-script (Mitigation, Third Party Advisory)
• https://www.vicarius.io/vsociety/posts/cve-2025-21333-elevated-privilege-exposure-in-windows-hyper-v-by-microsoft-mitigation-script (Mitigation, Third Party Advisory)

MITRE ATT&CK mitigations for this chain

• M1051 Update Software (for T1068) : Update software regularly by employing patch management for internal enterprise endpoints and servers.
• M1050 Exploit Protection (for T1068) : Security applications that look for behavior used during exploitation such as Windows Defender Exploit Guard (WDEG) and the Enhanced Mitigation Experience Toolkit (EMET) can be used to mitigate some exploitation behavior. Control flow integrity checking is another way to potentially identify and stop a software exploi
• M1048 Application Isolation and Sandboxing (for T1068) : Make it difficult for adversaries to advance their operation through exploitation of undiscovered or unpatched vulnerabilities by using sandboxing. Other types of virtualization and application microsegmentation may also mitigate the impact of some types of exploitation. Risks of additional exploits and weaknesses in t
• M1019 Threat Intelligence Program (for T1068) : Develop a robust cyber threat intelligence capability to determine what types and levels of threat may use software exploits and 0-days against a particular organization.
• M1038 Execution Prevention (for T1068) : Consider blocking the execution of known vulnerable drivers that adversaries may exploit to execute code in kernel mode. Validate driver block rules in audit mode to ensure stability prior to production deployment.
• M1041 Encrypt Sensitive Information (for T1003) : Ensure Domain Controller backups are properly secured.
• M1040 Behavior Prevention on Endpoint (for T1003) : On Windows 10, enable Attack Surface Reduction (ASR) rules to secure LSASS and prevent credential stealing.
• M1027 Password Policies (for T1003) : Ensure that local administrator accounts have complex, unique passwords across all systems on the network.
• M1017 User Training (for T1003) : Limit credential overlap across accounts and systems by training users and administrators not to use the same password for multiple accounts.
• M1026 Privileged Account Management (for T1003) : Windows: Do not put user or admin domain accounts in the local administrator groups across systems unless they are tightly controlled, as this is often equivalent to having a local administrator account with the same password on all systems. Follow best practices for design and administration of an enterprise network t

Detection Generic guidance

• Privilege Escalation: Alert on processes gaining SYSTEM/root unexpectedly, and on exploitation crashes of privileged services.
• Credential Access: Monitor for credential dumping, unusual LSASS access and sudden authentication from new sources.

Response checklist Generic guidance

1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.