CVE-2025-27491 is a high-severity use-after-free vulnerability (CWE-416) affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This vulnerability exists within the Windows Hyper-V component, which is Microsoft's native hypervisor technology used for creating and managing virtual machines. The flaw allows an authorized attacker with low privileges to execute arbitrary code remotely over a network. The vulnerability arises because the system improperly handles memory management, specifically freeing memory that is still in use, leading to potential exploitation paths such as remote code execution. The CVSS v3.1 base score is 7.1, indicating a high severity level, with attack vector being network-based (AV:N), requiring low privileges (PR:L), and user interaction (UI:R). The attack complexity is high (AC:H), meaning exploitation requires specific conditions or knowledge, and the scope remains unchanged (S:U). The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), meaning successful exploitation could lead to full system compromise. No known exploits are currently reported in the wild, and no patches or mitigation links have been provided yet. The vulnerability was reserved in late February 2025 and published in early April 2025, indicating recent discovery and disclosure. Given that Hyper-V is often used in enterprise environments for virtualization, this vulnerability could be leveraged to compromise virtualized workloads or host systems if exploited.

For European organizations, the impact of CVE-2025-27491 could be significant, especially for enterprises relying on Windows 10 Version 1809 with Hyper-V for virtualization infrastructure. Successful exploitation could lead to remote code execution, allowing attackers to gain control over affected systems, potentially leading to data breaches, disruption of services, or lateral movement within networks. This is particularly critical for sectors such as finance, healthcare, government, and critical infrastructure where virtualization is prevalent and data sensitivity is high. The requirement for low privileges and network access means that internal threat actors or attackers who have gained limited access could escalate their control. The high impact on confidentiality, integrity, and availability means that sensitive data could be exfiltrated or altered, and systems could be rendered unavailable, affecting business continuity. Additionally, the presence of user interaction as a requirement may limit automated exploitation but does not eliminate risk, especially in environments with frequent user activity or social engineering vectors. The lack of patches at the time of disclosure increases exposure risk until mitigations or updates are available.

Given the absence of an official patch at the time of disclosure, European organizations should implement several specific mitigations beyond generic advice: 1) Restrict network access to Hyper-V hosts by implementing strict network segmentation and firewall rules to limit exposure to trusted management networks only. 2) Enforce the principle of least privilege by ensuring that users and services interacting with Hyper-V have minimal necessary permissions, reducing the risk of exploitation by low-privileged attackers. 3) Monitor Hyper-V hosts and virtual machines for unusual activity or indicators of compromise, including unexpected process executions or memory anomalies, using advanced endpoint detection and response (EDR) tools. 4) Disable or limit unnecessary user interactions with Hyper-V management interfaces, and educate users about the risks of interacting with untrusted content or links that could trigger exploitation. 5) Maintain up-to-date backups of virtual machines and critical data to enable recovery in case of compromise. 6) Plan for rapid deployment of patches once Microsoft releases updates addressing this vulnerability, including testing and validation in controlled environments. 7) Consider upgrading affected systems to later Windows versions where this vulnerability is not present or has been resolved, if feasible within organizational policies.