Windows Projected File System Race Condition Privilege Escalation (CVE-2026-27927)

CVE-2026-27927 describes a race condition vulnerability within the Windows Projected File System (ProjFS). This vulnerability allows a locally authenticated attacker to elevate their privileges. The vulnerability exists due to improper synchronization when multiple threads or processes access shared resources within ProjFS concurrently. An attacker can exploit this by manipulating the timing of operations to gain unauthorized access or control. The vulnerability was published on April 14, 2026, and affects systems running the Windows Projected File System. Successful exploitation results in privilege escalation, granting the attacker higher-level access to the system. Defenders should prioritize patching this vulnerability.

Attack Chain

1. Attacker gains local access to a Windows system with ProjFS enabled.
2. Attacker crafts a malicious application or script to interact with the Projected File System.
3. The malicious application triggers concurrent access to shared resources within ProjFS.
4. Due to the race condition (CWE-362), the attacker manipulates the timing of file system operations.
5. This timing manipulation leads to improper access control within ProjFS.
6. The attacker gains unauthorized access to sensitive resources managed by ProjFS.
7. The attacker leverages this unauthorized access to execute privileged operations.
8. The attacker successfully elevates their privileges on the system.

Impact

Successful exploitation of CVE-2026-27927 allows a local attacker to elevate their privileges on a vulnerable Windows system. This could allow the attacker to gain complete control over the system, including access to sensitive data, installation of malware, and modification of system settings. The impact is significant because it allows an attacker with limited initial access to compromise the entire system. The number of potential victims is large, as it affects any Windows system using the Projected File System.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-27927 as referenced in the advisory URL.
• Monitor for unusual process creations or file system interactions related to ProjFS using process_creation and file_event logs.
• Deploy the Sigma rule to detect potential exploitation attempts of CVE-2026-27927 based on suspicious process execution.