CVE-2025-59259 is a vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0) affecting the Local Session Manager (LSM) component. The root cause is improper validation of the specified type of input, classified under CWE-1287, which relates to insufficient validation of input types leading to unexpected behavior. LSM is responsible for managing user sessions locally and coordinating session-related activities. The flaw allows an authorized attacker—meaning one with some level of access privileges—to send specially crafted input over the network to the LSM service. Due to the improper input validation, this can trigger a denial of service condition, likely by causing the LSM service to crash or become unresponsive, thereby disrupting session management and potentially affecting system availability. The CVSS v3.1 score is 6.5 (medium severity) with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), requiring privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), no confidentiality or integrity impact (C:N/I:N), but high impact on availability (A:H). The exploitability is moderate since it requires privileges but no user interaction, and the attack can be performed remotely over the network. No known exploits are currently reported in the wild, and no official patches have been released yet. This vulnerability is significant for environments still running Windows 10 Version 1809, which is an older but still in-use version in many organizations. The lack of patches means organizations must rely on mitigations until updates become available.

The primary impact of CVE-2025-59259 is on system availability, as exploitation results in denial of service by disrupting the Local Session Manager service. For European organizations, this can lead to interruptions in user session management, potentially causing system instability, forced reboots, or loss of access to critical applications and services. Industries with high dependency on Windows 10 Version 1809, such as manufacturing, healthcare, and government agencies, may experience operational disruptions. Since the vulnerability requires an authorized attacker with network access, insider threats or compromised accounts pose a significant risk. The lack of confidentiality or integrity impact reduces the risk of data breaches but does not diminish the operational impact. In sectors with strict uptime requirements, such as financial services or critical infrastructure, even temporary denial of service can have cascading effects on business continuity and regulatory compliance. The absence of known exploits currently limits immediate widespread impact but also means organizations must proactively prepare. The medium severity rating reflects a moderate but tangible risk to availability that should be addressed to maintain operational resilience.

1. Restrict network access to the Local Session Manager service by implementing strict firewall rules and network segmentation to limit exposure only to trusted hosts and networks. 2. Enforce the principle of least privilege by auditing and minimizing user privileges, especially for accounts with network access to affected systems. 3. Monitor system and network logs for unusual or suspicious activity targeting LSM or related session management components, including repeated connection attempts or malformed input patterns. 4. Prioritize upgrading affected systems from Windows 10 Version 1809 to a more recent, supported version of Windows 10 or Windows 11 where this vulnerability is not present or has been patched. 5. Implement robust endpoint detection and response (EDR) solutions capable of detecting anomalous behavior related to session management services. 6. Prepare incident response plans specifically addressing denial of service scenarios impacting session management to reduce downtime. 7. Stay informed on Microsoft security advisories for the release of official patches or workarounds and apply them promptly once available. 8. Consider isolating legacy systems that must run Windows 10 Version 1809 from critical network segments to reduce risk exposure.