CVE-2026-27926 Windows Cloud Files Mini Filter Driver Privilege Escalation

CVE-2026-27926 describes a vulnerability affecting the Windows Cloud Files Mini Filter Driver. This is a race condition vulnerability where concurrent execution using a shared resource without proper synchronization allows for privilege escalation. A locally authenticated attacker could exploit this vulnerability to gain elevated privileges on the system. The vulnerability resides within the core operating system component responsible for managing cloud file interactions, making it a potentially widespread issue across various Windows deployments that utilize cloud storage integration. Microsoft has assigned a CVSS v3.1 score of 7.0, indicating a high severity. This vulnerability requires local access but does not require user interaction, increasing its potential impact.

Attack Chain

1. The attacker gains local access to the target Windows system.
2. The attacker crafts a malicious application designed to trigger the race condition in the Cloud Files Mini Filter Driver.
3. The malicious application initiates concurrent operations involving shared resources managed by the affected driver.
4. Due to the race condition, the driver incorrectly handles the concurrent operations, leading to an exploitable state.
5. The attacker leverages the exploitable state to overwrite critical system data or execute arbitrary code within the context of the driver.
6. The successful exploitation leads to elevated privileges, allowing the attacker to perform actions normally restricted to administrators or the system.
7. The attacker can then install programs, view, change, or delete data, or create new accounts with full user rights.

Impact

A successful exploit of CVE-2026-27926 enables a local attacker to escalate their privileges on a Windows system. This could lead to complete system compromise, data theft, and the installation of malware. The number of potential victims is extensive, affecting any Windows system utilizing the vulnerable Cloud Files Mini Filter Driver. The primary impact is unauthorized access and control over the compromised system, potentially leading to significant data breaches or operational disruption.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-27926 as soon as possible by referencing the URL in the references section.
• Monitor for suspicious process creation events, especially those originating from unusual locations, that might be indicative of an exploit attempt; use process creation logs and the Sigma rules provided.
• Audit and monitor the execution of programs that interact heavily with the cloud file system (e.g., cloud storage clients, backup solutions) to detect anomalous behavior.
• Implement the provided Sigma rule to detect unexpected modifications to sensitive registry keys, which attackers might use to establish persistence after privilege escalation.