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 due to improper handling of input data within the WinSock driver, which is responsible for network socket operations. An authorized local attacker can exploit this flaw by crafting malicious input that overflows a stack buffer, leading to corruption of adjacent memory. This memory corruption can be leveraged to execute arbitrary code with elevated privileges, effectively allowing the attacker to escalate their privileges on the affected system. The vulnerability is classified under CWE-121, indicating a classic stack-based buffer overflow issue. The CVSS v3.1 base score is 7.0, reflecting a high severity level. The attack vector is local (AV:L), requiring the attacker to have low privileges (PR:L) but no user interaction (UI:N). The complexity is high (AC:H), suggesting exploitation requires specific conditions or expertise. The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), meaning successful exploitation can fully compromise the system. No known exploits are currently reported in the wild, and no official patches have been linked yet. This vulnerability affects a legacy Windows 10 version (1809), which may still be in use in certain environments. The flaw's presence in a core networking driver makes it particularly dangerous, as it could be used to bypass security boundaries and gain system-level control from a lower-privileged account.

For European organizations, this vulnerability poses a significant risk, especially for those still operating legacy Windows 10 Version 1809 systems, which may be common in industrial, governmental, or specialized enterprise environments where upgrading is slower. Exploitation could lead to full system compromise, allowing attackers to access sensitive data, disrupt critical services, or establish persistent footholds. The local attack vector means that insider threats or attackers who have gained limited access could escalate privileges to compromise entire systems. This is particularly concerning for sectors with strict data protection requirements under GDPR, as breaches could lead to regulatory penalties and reputational damage. Additionally, the high impact on system integrity and availability could disrupt business operations, affecting critical infrastructure or services. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate it, as attackers may develop exploits once the vulnerability details become widely known. Organizations relying on legacy Windows 10 deployments should consider this a priority issue.

Given the absence of an official patch, European organizations should implement several specific mitigations: 1) Conduct an inventory to identify all systems running Windows 10 Version 1809 and prioritize their upgrade to a supported, patched Windows version to eliminate exposure. 2) Enforce strict local access controls and minimize the number of users with local login privileges to reduce the risk of local exploitation. 3) Employ application whitelisting and endpoint protection solutions capable of detecting anomalous behavior indicative of buffer overflow exploitation attempts. 4) Use network segmentation to isolate legacy systems and limit lateral movement in case of compromise. 5) Monitor system logs and security events for unusual privilege escalation activities or crashes related to the WinSock driver. 6) Implement robust user account management and privilege separation to ensure attackers cannot easily gain initial local access. 7) Prepare incident response plans specifically addressing local privilege escalation scenarios. These measures go beyond generic advice by focusing on legacy system identification, access restriction, and behavioral detection tailored to this vulnerability's characteristics.