Microsoft Windows Hyper-V NT Kernel Integration VSP Heap-based Buffer Overflow
CVE-2025-21333 is a high-severity heap-based buffer overflow vulnerability in Windows 10 Version 21H2 from Microsoft, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists version 10.0.19044.5371 as the first without the flaw, so updating Windows 10 Version 21H2 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on January 14, 2025, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Windows 10 Version 21H2 to 10.0.19044.5371 or a later version.
- Update Windows 10 Version 22H2 to 10.0.19045.5371 or a later version.
- Update Windows 11 version 22H2 to 10.0.22621.4751 or a later version.
- CISA's required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows 10 Version 21H2 | 10.0.19044.0 up to, but not including, 10.0.19044.5371 | 10.0.19044.5371 |
| Microsoft | Windows 10 Version 22H2 | 10.0.19045.0 up to, but not including, 10.0.19045.5371 | 10.0.19045.5371 |
| Microsoft | Windows 11 version 22H2 | 10.0.22621.0 up to, but not including, 10.0.22621.4751 | 10.0.22621.4751 |
| Microsoft | Windows 11 version 22H3 | 10.0.22631.0 up to, but not including, 10.0.22631.4751 | 10.0.22631.4751 |
| Microsoft | Windows 11 Version 23H2 | 10.0.22631.0 up to, but not including, 10.0.22631.4751 | 10.0.22631.4751 |
| Microsoft | Windows 11 Version 24H2 | 10.0.26100.0 up to, but not including, 10.0.26100.2894 | 10.0.26100.2894 |
| Microsoft | Windows Server 2022, 23H2 Edition (Server Core installation) | 10.0.25398.0 up to, but not including, 10.0.25398.1369 | 10.0.25398.1369 |
| Microsoft | Windows Server 2025 | 10.0.26100.0 up to, but not including, 10.0.26100.2894 | 10.0.26100.2894 |
| Microsoft | Windows Server 2025 (Server Core installation) | 10.0.26100.0 up to, but not including, 10.0.26100.2894 | 10.0.26100.2894 |
| Microsoft | Windows 10 21h2 | before 10.0.19044.5371 | 10.0.19044.5371 |
| Microsoft | Windows 10 22h2 | before 10.0.19045.5371 | 10.0.19045.5371 |
| Microsoft | Windows 11 22h2 | before 10.0.22621.4751 | 10.0.22621.4751 |
| Microsoft | Windows 11 23h2 | before 10.0.22631.4751 | 10.0.22631.4751 |
| Microsoft | Windows 11 24h2 | before 10.0.26100.2894 | 10.0.26100.2894 |
| Microsoft | Windows Server 2022 23h2 | before 10.0.25398.1369 | 10.0.25398.1369 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (microsoft.com).
Official description
Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Heap-based Buffer Overflow
The product writes past the end of a buffer that was allocated on the heap.
How developers prevent this class of flaw
- Pre-design: Use a language or compiler that performs automatic bounds checking.
- Use an abstraction library to abstract away risky APIs. Not a complete solution.
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- vicarius.io/vsociety/posts/cve-2025-21333-elevated-privilege-exposure-in-windows-hyper-v-by-microsoft-detecti…Mitigation, Third Party Advisory
- vicarius.io/vsociety/posts/cve-2025-21333-elevated-privilege-exposure-in-windows-hyper-v-by-microsoft-mitigat…Mitigation, Third Party Advisory
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21333US Government Resource
Technical write-ups (may include proof of concept)
- exploit-db.com/exploits/52436Exploit, Third Party Advisory, VDB Entry
Recent Heap-based Buffer Overflow vulnerabilities
- 7.0 High severity
- 7.0 High severity
- 9.3 Critical severity
- 9.8 Critical severity
- 7.8 High severity
- 7.5 High severity
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