CVE-2025-21277 is a high-severity vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0) affecting the Microsoft Message Queuing (MSMQ) component. The vulnerability is classified as a CWE-126: Buffer Over-read, which occurs when a program reads data beyond the boundaries of a buffer. In this case, the MSMQ service improperly handles certain inputs, leading to an out-of-bounds read. This flaw can be triggered remotely without requiring authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). Exploiting this vulnerability results in a denial of service (DoS) condition, causing the MSMQ service or potentially the entire system to crash or become unresponsive. The vulnerability does not impact confidentiality or integrity but severely affects availability. Although no known exploits are currently reported in the wild, the ease of exploitation and the lack of required privileges make this a significant risk. The absence of a patch link suggests that remediation may not yet be available, emphasizing the need for immediate mitigation steps. The vulnerability was published on January 14, 2025, and was reserved in December 2024, indicating recent discovery and disclosure.

For European organizations, this vulnerability poses a substantial risk to operational continuity, especially for enterprises relying on Windows 10 Version 1809 systems running MSMQ for critical messaging and queuing services. A successful exploitation could disrupt internal communications, automated workflows, and application integrations that depend on MSMQ, leading to downtime and potential business process failures. Sectors such as finance, manufacturing, healthcare, and government agencies, which often use legacy Windows systems and MSMQ for messaging, could experience significant service interruptions. The denial of service could also be leveraged as part of a broader attack strategy to distract or degrade defenses during more complex intrusions. Given the vulnerability requires no privileges or user interaction, attackers could remotely trigger service outages, increasing the threat surface for remote and distributed work environments common in Europe.

European organizations should immediately identify and inventory all systems running Windows 10 Version 1809 with MSMQ enabled. Since no official patch is currently linked, organizations should implement network-level mitigations such as restricting access to MSMQ ports (typically TCP port 1801) using firewalls and network segmentation to limit exposure to untrusted networks. Employ intrusion detection and prevention systems (IDS/IPS) to monitor and block suspicious MSMQ traffic patterns indicative of exploitation attempts. Additionally, consider disabling MSMQ on systems where it is not essential to reduce the attack surface. For critical systems that must continue using MSMQ, apply strict access controls and monitor system stability closely. Organizations should also plan for an upgrade path to newer, supported Windows versions where this vulnerability is patched. Regularly review vendor advisories for patch releases and apply them promptly once available.