CVE-2026-20853 is a race condition vulnerability classified under CWE-362 affecting the Windows WalletService in Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability stems from improper synchronization when multiple threads or processes concurrently access shared resources, leading to a state where an unauthorized local attacker can manipulate the execution flow to elevate their privileges. This flaw allows attackers without prior authentication or user interaction to gain higher system privileges, potentially enabling full control over the affected system. The vulnerability's CVSS v3.1 score is 7.4, indicating high severity, with an attack vector limited to local access (AV:L), high attack complexity (AC:H), no privileges required (PR:N), and no user interaction (UI:N). The scope remains unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). Although no public exploits are known, the vulnerability poses a significant risk due to the potential for privilege escalation, which can be leveraged for further attacks such as lateral movement or persistence. The lack of available patches at the time of reporting necessitates immediate attention to mitigate risk. The vulnerability is particularly relevant for environments where Windows 10 Version 1809 remains in use, often in legacy or specialized systems. The WalletService component, responsible for managing digital wallet data, is critical, and compromise could lead to exposure or manipulation of sensitive user credentials or payment information. The race condition arises from concurrent execution paths accessing shared resources without proper locking or synchronization mechanisms, allowing attackers to exploit timing windows to corrupt or manipulate data or execution state.

For European organizations, the impact of CVE-2026-20853 is significant due to the potential for local privilege escalation on Windows 10 Version 1809 systems. Successful exploitation could allow attackers to gain administrative privileges, leading to full system compromise, data theft, or disruption of services. This is particularly critical for sectors such as finance, healthcare, government, and critical infrastructure, where confidentiality and integrity of data are paramount. Legacy systems still running Windows 10 1809 are especially vulnerable, as they may lack modern security controls and are often less frequently patched. The vulnerability could facilitate insider threats or attacks from compromised local accounts, enabling attackers to bypass security controls and escalate privileges without detection. Additionally, the high impact on availability could result in denial of service or system instability if exploited. Given the high attack complexity and local access requirement, remote exploitation is unlikely; however, organizations with shared workstations or multi-user environments face increased risk. The absence of known exploits in the wild provides a window for proactive mitigation, but the potential for future exploitation remains high.

1. Apply security patches immediately once Microsoft releases them for Windows 10 Version 1809 to address the race condition in WalletService. 2. Restrict local access to systems running Windows 10 1809 by enforcing strict access controls and limiting user privileges to the minimum necessary. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to monitor for unusual privilege escalation attempts or suspicious process behavior. 4. Conduct regular audits of user accounts and permissions to identify and remediate excessive privileges or unauthorized local accounts. 5. Where possible, upgrade affected systems to a more recent and supported Windows version that includes security improvements and mitigations against race conditions. 6. Employ system hardening techniques such as disabling unnecessary services, including WalletService if not required, to reduce the attack surface. 7. Educate users and administrators about the risks of local privilege escalation and the importance of reporting suspicious activity. 8. Use virtualization or sandboxing for high-risk applications to contain potential exploitation impacts. 9. Monitor system logs for anomalies related to WalletService or privilege escalation events to enable early detection. 10. Develop and test incident response plans specifically addressing local privilege escalation scenarios to ensure rapid containment and remediation.