CVE-2026-21241 is a use-after-free vulnerability classified under CWE-416 affecting the Windows Ancillary Function Driver for WinSock component in Microsoft Windows 11 version 22H3 (build 10.0.22631.0). This vulnerability arises when the system improperly manages memory, freeing an object while it is still in use, which can lead to arbitrary code execution or privilege escalation. An attacker with authorized local access and low privileges can exploit this flaw to elevate their privileges to a higher level, potentially gaining administrative control over the system. The attack does not require user interaction but has a high attack complexity, meaning it requires specific conditions or expertise to exploit successfully. The vulnerability impacts confidentiality, integrity, and availability, as an attacker could access sensitive data, modify system configurations, or disrupt system operations. Although no exploits are currently known in the wild, the presence of this vulnerability in a widely used operating system component makes it a significant risk. The vulnerability was reserved in December 2025 and published in February 2026, indicating recent discovery and disclosure. The lack of available patches at the time of reporting necessitates immediate attention to mitigation strategies to reduce exposure. The CVSS v3.1 base score of 7.0 reflects the high severity, with vector metrics indicating local attack vector, high attack complexity, low privileges required, no user interaction, unchanged scope, and high impact on confidentiality, integrity, and availability.

For European organizations, this vulnerability poses a significant risk, especially for enterprises and government agencies relying on Windows 11 version 22H3. Successful exploitation could allow attackers to escalate privileges locally, bypassing security controls and gaining administrative access. This could lead to unauthorized access to sensitive data, disruption of critical services, and potential lateral movement within networks. Organizations in sectors such as finance, healthcare, energy, and public administration are particularly vulnerable due to the critical nature of their operations and the high adoption rate of Windows 11. The requirement for local access limits remote exploitation but does not eliminate risk, as insider threats or compromised endpoints could be leveraged. The absence of known exploits in the wild provides a window for proactive defense, but the high impact on confidentiality, integrity, and availability necessitates urgent mitigation to prevent potential future attacks.

1. Apply official Microsoft patches immediately once released for Windows 11 version 22H3 to address CVE-2026-21241. 2. Until patches are available, restrict local access to critical systems by enforcing strict access controls and using endpoint protection solutions to monitor and block suspicious activities. 3. Implement least privilege principles to minimize the number of users with local access rights that could exploit this vulnerability. 4. Employ application whitelisting and behavior-based detection tools to identify anomalous privilege escalation attempts. 5. Conduct regular audits of user accounts and permissions to detect and remediate unauthorized privilege changes. 6. Educate IT staff and users about the risks of local privilege escalation vulnerabilities and encourage reporting of unusual system behavior. 7. Use network segmentation to isolate critical systems and reduce the impact of potential exploitation. 8. Monitor system logs and security alerts for indicators of exploitation attempts related to WinSock or privilege escalation activities.