CVE-2025-21379 is a use-after-free vulnerability (CWE-416) identified in the DHCP Client Service component of Microsoft Windows Server 2025, specifically affecting the Server Core installation version 10.0.26100.0. This vulnerability allows a remote attacker to execute arbitrary code on the affected system by sending specially crafted DHCP responses that trigger the use-after-free condition in the DHCP client. The flaw arises because the DHCP client improperly manages memory, freeing objects prematurely and then dereferencing them, which can lead to memory corruption. Exploitation requires the attacker to be able to influence DHCP traffic received by the server, which typically involves network-level access or man-in-the-middle positioning. The CVSS v3.1 score is 7.1 (high), reflecting that the attack vector is adjacent network (AV:A), requiring high attack complexity (AC:H), no privileges (PR:N), but some user interaction (UI:R). The vulnerability impacts confidentiality, integrity, and availability, potentially allowing full system compromise including remote code execution. No patches or known exploits are currently available, but the vulnerability is publicly disclosed and should be considered a significant risk. The Server Core installation is often used in enterprise and data center environments, making this vulnerability particularly relevant for critical infrastructure and cloud services running Windows Server 2025.

For European organizations, this vulnerability poses a significant risk to server infrastructure, especially those relying on Windows Server 2025 Server Core installations for critical services. Successful exploitation could lead to remote code execution, allowing attackers to gain control over affected servers, exfiltrate sensitive data, disrupt services, or pivot within internal networks. This could impact confidentiality through data breaches, integrity by unauthorized modifications, and availability by causing system crashes or denial of service. Given the role of DHCP in network configuration, exploitation could also disrupt network operations. Organizations in sectors such as finance, government, healthcare, and telecommunications, which heavily depend on Windows Server environments, could face operational disruptions and regulatory consequences under GDPR if data is compromised. The lack of available patches increases the urgency for proactive mitigation to prevent exploitation.

Until official patches are released, European organizations should implement several specific mitigations: 1) Restrict DHCP traffic to trusted network segments and limit exposure of DHCP client services to untrusted networks, using network segmentation and firewall rules. 2) Monitor DHCP traffic for anomalous or unexpected DHCP responses that could indicate exploitation attempts. 3) Employ network intrusion detection/prevention systems (IDS/IPS) with updated signatures to detect suspicious DHCP packets. 4) Harden server configurations by disabling unnecessary network services and minimizing the attack surface on Windows Server 2025 Server Core installations. 5) Prepare for rapid deployment of patches once available by maintaining an up-to-date asset inventory and patch management process. 6) Educate system administrators about the vulnerability and ensure strict access controls and logging to detect potential exploitation. 7) Consider isolating critical servers from networks where DHCP traffic could be manipulated by attackers.