CVE-2025-21335 is a use-after-free vulnerability classified under CWE-416, found in the Windows Hyper-V NT Kernel Integration Virtual Service Provider (VSP) component on Windows 10 Version 21H2 (build 19043.0). The vulnerability arises when the system improperly manages memory, allowing an attacker to reference freed memory, potentially leading to arbitrary code execution or privilege escalation. Specifically, this flaw enables an attacker with limited privileges and local access to elevate their privileges to SYSTEM level without requiring user interaction. The CVSS v3.1 score is 7.8, indicating high severity, with attack vector local (AV:L), low attack complexity (AC:L), privileges required low (PR:L), no user interaction (UI:N), and impacts on confidentiality, integrity, and availability all rated high (C:H/I:H/A:H). The vulnerability is currently published but lacks publicly available patches or known exploits in the wild. The flaw affects the Hyper-V virtualization stack, which is widely used in enterprise environments for running virtual machines. Exploiting this vulnerability could allow attackers to escape virtual machine constraints or compromise host systems, posing a significant risk to virtualized environments.

For European organizations, the impact of CVE-2025-21335 is substantial, especially for those heavily reliant on Windows 10 21H2 and Hyper-V virtualization technology. Successful exploitation can lead to full system compromise, allowing attackers to gain SYSTEM-level privileges, bypass security controls, and potentially move laterally within networks. This threatens the confidentiality of sensitive data, integrity of critical systems, and availability of services. Enterprises running virtualized workloads, cloud service providers, and organizations using Hyper-V for desktop or server virtualization are at heightened risk. The vulnerability could be leveraged to deploy ransomware, steal intellectual property, or disrupt critical infrastructure. Given the local attack vector, insider threats or compromised user accounts could exploit this flaw to escalate privileges. The absence of known exploits currently provides a window for proactive defense, but the high severity score underscores the urgency of mitigation.

Organizations should prepare to deploy official patches from Microsoft as soon as they become available. In the interim, restrict local access to systems running Windows 10 Version 21H2 with Hyper-V enabled, limiting user privileges to the minimum necessary. Employ strict access controls and monitor for unusual privilege escalation activities or suspicious behavior indicative of exploitation attempts. Disable Hyper-V if it is not required to reduce the attack surface. Use endpoint detection and response (EDR) tools to detect anomalous memory operations or kernel-level exploits. Regularly audit and update virtualization host configurations to follow security best practices. Additionally, segment networks to contain potential breaches and maintain up-to-date backups to recover from possible attacks. Educate users about the risks of local privilege escalation and enforce strong authentication mechanisms to reduce the likelihood of initial compromise.