What is the CVSS score of CVE-2026-21248?

CVE-2026-21248 has a CVSS 3.1 base score of 7.3 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.0%.

Which versions of Windows are affected by CVE-2026-21248?

A high-severity heap buffer overflow in Windows Hyper-V allows authenticated attackers with local access to execute arbitrary code, potentially compromising virtualized environments and hosted…. A patch is available.

Is there a public PoC exploit available for CVE-2026-21248?

Yes, a public proof-of-concept exploit is available for CVE-2026-21248. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2026-21248?

Within 24 hours: Inventory all Windows Hyper-V deployments and identify systems with untrusted user access; disable guest VM access for non-essential accounts. Within 7 days: Implement strict role-based access controls limiting Hyper-V administrative privileges, enable Enhanced Session Mode restrictions, and segment Hyper-V hosts from general user networks. Within 30 days: Monitor for vendor patch release and prepare deployment; conduct security assessment of all Hyper-V guest VMs for lateral movement risk.

Windows CVE-2026-21248

HIGH

Heap-based Buffer Overflow (CWE-122)

2026-02-10 secure@microsoft.com

Windows Hyper-V Buffer Overflow Heap Overflow Windows Server 2025 Windows 10 1809 Windows 10 21h2 Windows 10 1607 Windows 11 24h2 Windows Server 2022 23h2 Windows 11 23h2 Windows 11 25h2 Windows Server 2016 Windows Server 2022 Windows Server 2019 Windows 10 22h2 Microsoft

7.3

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

7.3 HIGH

AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

Attack Vector

Local

Attack Complexity

Low

Privileges Required

Low

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 22:02 vuln.today

CVE Published

Feb 10, 2026 - 18:16 nvd

HIGH 7.3

DescriptionCVE.org

Heap-based buffer overflow in Windows Hyper-V allows an authorized attacker to execute code locally.

AnalysisAI

Heap overflow in Windows Hyper-V enables authenticated local users to achieve arbitrary code execution with high privileges on affected Windows and Windows Server systems. An attacker with local access and user-level permissions can trigger memory corruption through user interaction to compromise system integrity and confidentiality. This vulnerability affects Windows 10 1809, Windows Server 2025, and related Hyper-V implementations with no patch currently available.

Technical ContextAI

Classified as CWE-122 (Heap-based Buffer Overflow). Affects Windows 10 1607. Heap-based buffer overflow in Windows Hyper-V allows an authorized attacker to execute code locally.