CVE-2025-29955 is a vulnerability identified in Microsoft Windows Server 2025, specifically affecting the Server Core installation variant. The issue stems from improper input validation within the Windows Hyper-V component. Hyper-V is Microsoft's native hypervisor used to create and manage virtual machines on Windows systems. Improper input validation means that the software fails to correctly verify or sanitize input data, which can lead to unexpected behavior. In this case, the vulnerability allows an unauthorized local attacker to cause a denial of service (DoS) condition. The attacker does not require any privileges (PR:N) or user interaction (UI:N) to exploit this flaw, but must have local access to the system (AV:L). The vulnerability does not impact confidentiality or integrity but affects availability, as it can cause the Hyper-V service or the host system to become unresponsive or crash. The CVSS v3.1 base score is 6.2, categorized as medium severity. The scope is unchanged (S:U), meaning the impact is confined to the vulnerable component and does not extend to other system components. No known exploits are currently reported in the wild, and no patches have been published at the time of this analysis. The vulnerability is tracked under CWE-20, which relates to improper input validation, a common root cause for many security issues. Given the critical role of Hyper-V in virtualization environments, this vulnerability could disrupt virtualized workloads and services running on affected Windows Server 2025 installations, particularly in environments relying on Server Core for minimal footprint and enhanced security posture.

For European organizations, the impact of CVE-2025-29955 can be significant, especially for enterprises and service providers that utilize Windows Server 2025 with Hyper-V for virtualization infrastructure. The denial of service could lead to downtime of critical virtual machines, affecting business continuity, service availability, and potentially causing financial losses. Industries such as finance, healthcare, telecommunications, and government agencies that rely heavily on virtualized environments for critical applications may experience operational disruptions. Additionally, organizations using Server Core installations for hardened security environments may find remediation challenging without impacting service availability. Although the vulnerability requires local access, insider threats or compromised internal systems could exploit this flaw to disrupt services. The lack of confidentiality or integrity impact reduces risks related to data breaches, but availability disruptions can still have cascading effects on dependent systems and services. The absence of known exploits currently provides a window for proactive mitigation before active exploitation emerges.

To mitigate CVE-2025-29955 effectively, European organizations should: 1) Monitor for official patches or updates from Microsoft and prioritize their deployment as soon as they become available, especially in production environments running Windows Server 2025 Server Core. 2) Restrict local access to Hyper-V hosts by enforcing strict access controls, limiting administrative privileges, and using network segmentation to isolate management interfaces. 3) Implement robust monitoring and alerting for unusual Hyper-V service behavior or crashes to detect potential exploitation attempts early. 4) Employ application whitelisting and endpoint protection solutions that can detect anomalous activities related to Hyper-V processes. 5) Conduct regular security audits and vulnerability assessments focusing on virtualization infrastructure to identify and remediate configuration weaknesses. 6) Consider temporary workarounds such as disabling unnecessary Hyper-V features or services if feasible, until patches are applied. 7) Educate internal staff about the risks of local exploitation and enforce policies to prevent unauthorized physical or remote local access to critical servers.