CVE-2025-21335 is a high-severity use-after-free vulnerability (CWE-416) affecting the Windows Hyper-V NT Kernel Integration VSP component in Microsoft Windows 10 Version 21H2 (build 10.0.19043.0). This vulnerability allows an attacker with limited privileges (low privilege user) on a vulnerable system to elevate their privileges to SYSTEM level by exploiting improper memory management in the Hyper-V Virtual Service Provider (VSP) interface. The use-after-free condition arises when the system incorrectly handles memory objects, leading to the possibility of executing arbitrary code or causing system instability. The vulnerability does not require user interaction and can be exploited locally, meaning an attacker must have some access to the system but can then escalate privileges without further user involvement. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and low privileges required. No known exploits are currently reported in the wild, and no official patches have been linked yet, indicating that mitigation and remediation efforts are critical to prevent exploitation once exploit code becomes available. This vulnerability specifically targets the Windows 10 21H2 version, which is widely used in enterprise environments, particularly those leveraging Hyper-V virtualization for workload isolation and cloud infrastructure.

For European organizations, the impact of CVE-2025-21335 is significant due to the widespread use of Windows 10 21H2 in corporate environments and the reliance on Hyper-V for virtualization and cloud services. Successful exploitation could allow attackers to gain SYSTEM-level privileges, enabling full control over affected machines. This could lead to data breaches, lateral movement within networks, deployment of ransomware, or disruption of critical services. Confidentiality is at high risk as attackers could access sensitive data; integrity could be compromised by unauthorized code execution or system modifications; availability could be affected through system crashes or denial-of-service conditions. Organizations in sectors such as finance, government, healthcare, and critical infrastructure are particularly vulnerable due to the sensitive nature of their data and the criticality of their systems. The lack of known exploits currently provides a window for proactive mitigation, but the potential for rapid weaponization once exploits emerge necessitates urgent attention.

European organizations should immediately identify all systems running Windows 10 Version 21H2 with Hyper-V enabled. Until official patches are released, apply the following mitigations: 1) Restrict local user privileges to the minimum necessary to reduce the risk of local exploitation. 2) Disable or limit Hyper-V usage on endpoints where virtualization is not required, reducing the attack surface. 3) Implement strict application whitelisting and endpoint detection and response (EDR) solutions to detect anomalous behavior indicative of exploitation attempts. 4) Monitor system logs and Hyper-V event logs for unusual activity related to memory management or privilege escalation attempts. 5) Prepare for rapid deployment of official patches once available by maintaining an up-to-date asset inventory and patch management process. 6) Educate IT staff about the vulnerability specifics to ensure timely response and incident handling. 7) Consider network segmentation to isolate Hyper-V hosts from less trusted network segments to limit lateral movement.