CVE-2026-20857 is a vulnerability classified under CWE-822 (Untrusted Pointer Dereference) found in the Windows Cloud Files Mini Filter Driver component of Microsoft Windows 11 Version 25H2 (build 10.0.26200.0). This flaw arises when the driver dereferences pointers that have not been properly validated or sanitized, allowing an attacker with authorized local access to manipulate pointer values. Exploiting this vulnerability enables privilege escalation, granting the attacker higher system privileges than originally assigned. The vulnerability does not require user interaction and has a low attack complexity, but it does require local privileges, meaning the attacker must already have some level of access to the system. The impact includes full compromise of confidentiality, integrity, and availability of the affected system, as elevated privileges can lead to arbitrary code execution, installation of persistent malware, or disruption of system services. Although no known exploits are currently reported in the wild, the vulnerability's characteristics and high CVSS score (7.8) indicate a significant risk once exploit code becomes available. The vulnerability was publicly disclosed on January 13, 2026, and no official patches have been linked yet, emphasizing the need for vigilance. The Cloud Files Mini Filter Driver is integral to Windows' file synchronization and cloud integration features, making this vulnerability particularly relevant for environments leveraging cloud storage and synchronization. Attackers exploiting this flaw could bypass security controls and gain administrative access, posing a serious threat to enterprise environments.

For European organizations, the impact of CVE-2026-20857 is considerable due to the widespread use of Windows 11 in corporate and governmental environments. Privilege escalation vulnerabilities allow attackers to bypass security boundaries, potentially leading to full system compromise. This can result in unauthorized access to sensitive data, disruption of critical services, and the deployment of ransomware or other malware. Organizations relying on cloud file synchronization features are particularly vulnerable, as the flaw resides in the Cloud Files Mini Filter Driver. The compromise of privileged accounts can also facilitate lateral movement within networks, increasing the risk of large-scale breaches. Critical infrastructure sectors such as finance, healthcare, and government agencies in Europe could face operational disruptions and data breaches. The absence of known exploits currently provides a window for proactive mitigation, but the high severity and ease of exploitation once local access is gained make timely patching and access control essential to prevent exploitation.

1. Monitor Microsoft security advisories closely and apply official patches immediately upon release to remediate the vulnerability. 2. Restrict local access to Windows 11 systems, especially those running version 25H2 (build 10.0.26200.0), by enforcing strict access controls and least privilege principles. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to detect anomalous behavior related to privilege escalation attempts. 4. Disable or limit the use of cloud file synchronization features if not essential, reducing the attack surface related to the Cloud Files Mini Filter Driver. 5. Conduct regular audits of user privileges and remove unnecessary local administrative rights to minimize the pool of potential attackers. 6. Employ network segmentation to contain potential lateral movement if a system is compromised. 7. Educate IT staff and users about the risks of local privilege escalation and the importance of reporting suspicious system behavior. 8. Utilize advanced logging and monitoring to detect attempts to exploit pointer dereference vulnerabilities or unusual driver activity. These targeted measures go beyond generic advice by focusing on the specific affected component and attack vector.