CVE-2025-21418 is a heap-based buffer overflow vulnerability classified under CWE-122, affecting the Windows Ancillary Function Driver for WinSock in Windows 10 Version 1507 (build 10.0.10240.0). The vulnerability arises due to improper handling of memory buffers within the WinSock driver, which is responsible for network socket operations. An attacker with low privileges on the affected system can exploit this flaw to execute arbitrary code in kernel mode, thereby elevating their privileges to SYSTEM level. The vulnerability does not require user interaction and has a low attack complexity, but requires local access and low privileges to initiate the exploit. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability. The flaw was reserved in December 2024 and published in February 2025, with no known exploits in the wild at the time of disclosure. No official patches have been linked yet, indicating that affected systems remain vulnerable until updates are released or mitigations applied. This vulnerability is particularly critical for legacy Windows 10 installations that have not been updated or upgraded, as attackers gaining SYSTEM privileges can fully compromise affected machines and potentially pivot within networks.

The vulnerability allows local attackers to escalate privileges from low-level accounts to SYSTEM, granting full control over the affected system. This can lead to unauthorized access to sensitive data, installation of persistent malware, disruption of system services, and lateral movement within enterprise networks. The compromise of critical systems running Windows 10 Version 1507 could result in significant operational disruption and data breaches. Since the vulnerability affects core networking components, exploitation could also impact network reliability and availability. Organizations relying on legacy Windows 10 versions, especially in sectors such as government, healthcare, finance, and critical infrastructure, face heightened risks. The lack of a patch at the time of disclosure increases the window of exposure, making timely mitigation essential to prevent exploitation.

Organizations should prioritize upgrading affected systems from Windows 10 Version 1507 to a supported and patched Windows version to eliminate exposure. In the absence of an official patch, applying strict access controls to limit local user privileges can reduce the risk of exploitation. Employing endpoint detection and response (EDR) solutions to monitor for suspicious local privilege escalation attempts is recommended. Network segmentation and the principle of least privilege should be enforced to contain potential compromises. Regularly auditing and removing legacy systems from critical environments will reduce the attack surface. Additionally, organizations should stay alert for official patches or security advisories from Microsoft and apply updates immediately upon release. Implementing application whitelisting and restricting the execution of unauthorized code can further mitigate exploitation risks.