CVE-2026-20810 is a vulnerability classified under CWE-590, which involves the improper freeing of memory not allocated on the heap, specifically within the Windows Ancillary Function Driver for WinSock on Windows 10 Version 1809 (build 10.0.17763.0). This flaw arises when the system attempts to free memory that was not dynamically allocated on the heap, leading to undefined behavior that can be exploited by an authorized local attacker to escalate privileges. The vulnerability requires the attacker to have local access with some level of privileges (PR:L) but does not require user interaction (UI:N). The attack vector is local (AV:L), and the vulnerability affects confidentiality, integrity, and availability (C:H/I:H/A:H), indicating that successful exploitation can lead to full system compromise. The scope is unchanged (S:U), meaning the impact is confined to the vulnerable component on the same system. The CVSS score of 7.8 reflects a high severity level. Currently, there are no known exploits in the wild, and no official patches have been linked, although the vulnerability was published on January 13, 2026. The flaw is significant because it allows privilege escalation, which can be a stepping stone for attackers to gain administrative control, bypass security controls, and execute arbitrary code with elevated rights. The affected product is an older Windows 10 version (1809), which may still be in use in some organizations due to legacy application dependencies or delayed upgrade cycles.

For European organizations, this vulnerability poses a significant risk, particularly for those still operating Windows 10 Version 1809 in production environments. Successful exploitation can lead to full system compromise, allowing attackers to bypass security restrictions, access sensitive data, and disrupt services. Critical infrastructure sectors such as finance, healthcare, and government agencies that rely on Windows 10 1809 could face operational disruptions and data breaches. The local attack vector means that attackers must already have some form of access, which could be gained through phishing, insider threats, or other initial footholds. Once local access is obtained, this vulnerability facilitates privilege escalation, increasing the severity of an attack. Organizations with weak internal segmentation or insufficient endpoint protection are particularly vulnerable. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as exploit code could be developed following public disclosure. The lack of an official patch at the time of publication means organizations must rely on interim mitigations to reduce exposure.

1. Upgrade to a supported and fully patched version of Windows, preferably a more recent Windows 10 build or Windows 11, to eliminate the vulnerability. 2. If upgrading is not immediately feasible, implement strict local user privilege management to minimize the number of users with local access rights that could exploit this vulnerability. 3. Employ application whitelisting and endpoint detection and response (EDR) solutions to monitor for suspicious local activity indicative of privilege escalation attempts. 4. Enforce network segmentation and limit lateral movement within internal networks to reduce the impact of a compromised local account. 5. Monitor Windows event logs and security telemetry for anomalies related to WinSock driver activity or unexpected memory management errors. 6. Prepare for patch deployment by tracking Microsoft security advisories and applying updates promptly once available. 7. Conduct regular security awareness training to reduce the likelihood of initial local access through social engineering or phishing. 8. Use least privilege principles for all user accounts and services to limit the potential attack surface.