CVE-2026-20810 is a vulnerability categorized under CWE-590, which involves the improper freeing of memory that was not allocated on the heap. Specifically, this flaw exists in the Windows Ancillary Function Driver for WinSock in Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability allows an authorized local attacker to perform a free operation on memory not allocated on the heap, leading to undefined behavior such as memory corruption. This can be exploited to escalate privileges locally, granting the attacker elevated rights on the affected system. The CVSS 3.1 base score of 7.8 reflects a high severity due to the impact on confidentiality, integrity, and availability, combined with relatively low attack complexity and no requirement for user interaction. The attacker must have some level of local privileges (PR:L), but no further authentication or user involvement is necessary. The vulnerability is currently published with no known exploits in the wild and no patches released, indicating a window of exposure. The flaw arises from improper memory management in a core networking component, which could be leveraged to execute arbitrary code or disrupt system operations, potentially compromising the entire system. Given the critical role of WinSock in network communications, exploitation could have broad implications for system stability and security.

For European organizations, the impact of CVE-2026-20810 is significant, especially for those still operating legacy Windows 10 Version 1809 systems. Successful exploitation allows local attackers to escalate privileges, potentially leading to full system compromise. This can result in unauthorized access to sensitive data, disruption of services, and the ability to deploy further malware or ransomware. Critical infrastructure sectors such as finance, healthcare, energy, and government agencies are particularly vulnerable due to their reliance on Windows-based systems and the potential high value of the data and services they manage. The vulnerability could facilitate lateral movement within networks, increasing the risk of widespread compromise. Additionally, organizations with less mature patch management or endpoint security practices may face prolonged exposure. The lack of available patches at the time of disclosure further exacerbates the risk, requiring immediate compensating controls to mitigate potential exploitation.

1. Upgrade affected systems to a supported and patched version of Windows, ideally moving away from Windows 10 Version 1809, which is out of mainstream support. 2. Restrict local access to systems running the vulnerable version by enforcing strict access controls and limiting administrative privileges to trusted personnel only. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to monitor and block suspicious local activities indicative of exploitation attempts. 4. Conduct regular audits of user accounts and privileges to minimize the number of users with local access rights. 5. Employ network segmentation to isolate critical systems and reduce the attack surface for local privilege escalation. 6. Monitor system logs and security events for anomalies related to memory corruption or unusual WinSock driver behavior. 7. Prepare incident response plans specifically addressing local privilege escalation scenarios to enable rapid containment and remediation. 8. Stay informed on Microsoft’s security advisories for the release of patches or workarounds related to this vulnerability.