CVE-2025-54099 is a stack-based buffer overflow vulnerability identified in the Windows Ancillary Function Driver for WinSock component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This vulnerability arises from improper handling of input data within the WinSock driver, leading to a buffer overflow on the stack. An attacker with authorized local access and low privileges can exploit this flaw to execute arbitrary code with elevated privileges, effectively allowing local privilege escalation. The vulnerability does not require user interaction but has a high attack complexity, meaning exploitation demands specific conditions or expertise. The CVSS v3.1 base score is 7.0, reflecting high impact on confidentiality, integrity, and availability, but limited by the requirement for local access and high complexity. No public exploits or active exploitation in the wild have been reported as of the publication date. The vulnerability is categorized under CWE-121, indicating a classic stack-based buffer overflow issue. The affected version is specifically Windows 10 Version 1809, which is an older release, and no patch links were provided at the time of disclosure, suggesting that remediation is pending or in progress. This vulnerability poses a significant risk to systems still running this legacy OS version, particularly in environments where local user accounts have limited restrictions or where attackers can gain local access through other means.

For European organizations, the impact of CVE-2025-54099 can be substantial, especially in sectors relying on legacy Windows 10 Version 1809 installations. Successful exploitation allows attackers to escalate privileges locally, potentially leading to full system compromise. This can result in unauthorized access to sensitive data, disruption of critical services, and the ability to deploy further malware or ransomware. Organizations with strict regulatory requirements for data protection, such as those governed by GDPR, face increased compliance risks if this vulnerability is exploited. The requirement for local access limits remote exploitation but does not eliminate risk, as attackers may leverage phishing, social engineering, or insider threats to gain initial footholds. The absence of a patch at disclosure heightens the urgency for mitigation. Critical infrastructure, government agencies, healthcare, and financial institutions in Europe are particularly vulnerable due to their reliance on legacy systems and the high value of their data and services. The vulnerability's impact on confidentiality, integrity, and availability underscores the need for immediate attention to prevent potential breaches or service outages.

1. Immediate mitigation should focus on restricting local access to systems running Windows 10 Version 1809 by enforcing strict access controls and limiting user privileges to the minimum necessary. 2. Monitor system logs and security events for signs of local privilege escalation attempts, such as unusual process creations or access violations related to WinSock components. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to detect and block suspicious activities indicative of exploitation attempts. 4. Where possible, upgrade affected systems to a supported and patched version of Windows 10 or later to eliminate exposure to this vulnerability. 5. Until a patch is released, consider isolating legacy systems from critical network segments to reduce the risk of lateral movement following exploitation. 6. Educate users about the risks of local access and enforce policies to prevent unauthorized physical or remote access to endpoints. 7. Regularly review and update security configurations related to network drivers and ancillary services to minimize attack surface. 8. Stay informed about vendor advisories and apply official patches promptly once available to fully remediate the vulnerability.