CVE-2026-20844 is a use-after-free vulnerability classified under CWE-416 found in the Windows Clipboard Server component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability arises from improper memory management where a previously freed object is accessed, leading to undefined behavior that attackers can exploit to escalate privileges locally. The attack vector is local, requiring the attacker to have access to the system but no prior privileges or user interaction. The vulnerability impacts confidentiality, integrity, and availability, as it can allow arbitrary code execution with elevated privileges, potentially compromising the entire system. The CVSS v3.1 score is 7.4 (high), reflecting the high impact but mitigated by the requirement for local access and high attack complexity. No public exploits or patches are currently available, increasing the urgency for organizations to monitor for updates. The Clipboard Server is a critical Windows component that manages clipboard operations between processes, and exploitation could allow attackers to manipulate clipboard data or execute malicious code. This vulnerability is particularly concerning for environments where legacy Windows 10 1809 systems remain in use, as these systems no longer receive mainstream support and may lack other security improvements present in newer versions.

For European organizations, this vulnerability poses a significant risk, especially in sectors relying on legacy Windows 10 1809 systems such as manufacturing, healthcare, and government agencies. Successful exploitation can lead to local privilege escalation, enabling attackers to gain administrative control, bypass security controls, and deploy malware or ransomware. This could result in data breaches, operational disruption, and loss of sensitive information. The requirement for local access limits remote exploitation but does not eliminate risk in environments with shared workstations, remote desktop access, or insider threats. The lack of patches increases exposure time, and organizations with delayed update cycles or unsupported systems are particularly vulnerable. The Clipboard Server's role in inter-process communication means exploitation could facilitate lateral movement within networks, amplifying the threat. Additionally, the high confidentiality, integrity, and availability impact could affect compliance with European data protection regulations such as GDPR if sensitive data is compromised.

1. Restrict local access to systems running Windows 10 Version 1809 by enforcing strict access controls and monitoring user activity. 2. Disable or limit clipboard sharing features where feasible, especially in high-security environments, to reduce attack surface. 3. Deploy advanced endpoint detection and response (EDR) solutions capable of identifying anomalous memory operations and privilege escalation attempts related to clipboard processes. 4. Implement application whitelisting and least privilege principles to minimize the impact of potential exploitation. 5. Monitor for unusual clipboard or process behavior using security information and event management (SIEM) tools. 6. Prepare for patch deployment by tracking Microsoft advisories and testing updates in controlled environments to ensure rapid remediation once patches are released. 7. Consider upgrading affected systems to supported Windows versions with ongoing security updates to reduce exposure to legacy vulnerabilities. 8. Educate users about the risks of local privilege escalation and enforce policies to prevent unauthorized software installation or execution.