CVE-2026-24290: Windows Projected File System Privilege Escalation

CVE-2026-24290 Overview

CVE-2026-24290 is an improper access control vulnerability in the Windows Projected File System (ProjFS) that enables an authorized attacker to elevate privileges locally. The Windows Projected File System is a feature that allows file system providers to project hierarchical data from a backing data store into a virtual file system, commonly used by applications like Windows Defender and various virtualization solutions.

This vulnerability allows a local attacker with low-level privileges to exploit flawed access control mechanisms within ProjFS to gain elevated system privileges, potentially achieving complete control over the affected Windows system.

Critical Impact

Local privilege escalation vulnerability in Windows Projected File System could allow attackers with initial system access to gain SYSTEM-level privileges and fully compromise affected Windows systems.

Affected Products

• Windows Projected File System (ProjFS)
• Windows Operating Systems with ProjFS enabled

Discovery Timeline

• March 10, 2026 - CVE-2026-24290 published to NVD
• March 11, 2026 - Last updated in NVD database

Technical Details for CVE-2026-24290

Vulnerability Analysis

This vulnerability stems from improper access control (CWE-284) within the Windows Projected File System component. The flaw exists in how ProjFS handles permission validation during certain file system operations, allowing authenticated users to bypass security boundaries and execute code with elevated privileges.

The attack requires local access to the target system and the attacker must have at least low-level privileges to exploit this vulnerability. However, no user interaction is required for successful exploitation, making this vulnerability particularly dangerous in scenarios where attackers have already gained initial foothold through other means such as phishing or social engineering.

Successful exploitation results in complete compromise of confidentiality, integrity, and availability of the affected system, as the attacker can gain SYSTEM-level privileges.

Root Cause

The root cause of CVE-2026-24290 is classified under CWE-284 (Improper Access Control). The Windows Projected File System fails to properly enforce access control checks during specific file system operations. This allows a low-privileged user to manipulate ProjFS operations in a way that bypasses intended security restrictions, ultimately leading to privilege escalation.

The improper access control likely occurs during the handling of virtualized file operations, where the system fails to adequately validate the caller's permissions before executing privileged actions on behalf of the requesting process.

Attack Vector

The attack vector for this vulnerability is local, meaning an attacker must have prior access to the target system. The exploitation sequence typically involves:

1. The attacker gains initial access to a Windows system with an unprivileged user account
2. The attacker identifies that ProjFS is enabled and accessible
3. By crafting specific file system requests to the Projected File System, the attacker can trigger the improper access control condition
4. The vulnerability allows the attacker's code to execute with elevated (typically SYSTEM) privileges
5. With elevated privileges, the attacker can install malware, access sensitive data, create new privileged accounts, or move laterally within the network

For detailed technical information about exploitation mechanics, refer to the Microsoft Security Update for CVE-2026-24290.

Detection Methods for CVE-2026-24290

Indicators of Compromise

• Unusual process execution chains involving ProjFS-related processes with unexpected parent-child relationships
• Processes spawned with SYSTEM privileges from low-privileged user sessions
• Anomalous file system activity targeting virtualized or projected file paths
• Unexpected privilege escalation events logged in Windows Security Event logs

Detection Strategies

• Monitor Windows Security Event logs for Event ID 4672 (Special privileges assigned to new logon) from unusual sources
• Deploy endpoint detection rules to identify suspicious interactions with the Windows Projected File System driver (PrjFlt.sys)
• Implement behavioral analysis to detect privilege escalation patterns following ProjFS operations
• Use SentinelOne's behavioral AI to detect anomalous privilege escalation attempts in real-time

Monitoring Recommendations

• Enable verbose logging for Windows file system operations and audit privilege use
• Configure Windows Advanced Audit Policy to log object access for projected file system paths
• Implement real-time alerting for any process gaining SYSTEM privileges from user-level execution context
• Deploy SentinelOne agents configured with Storyline technology to track full attack chains and correlate ProjFS-related anomalies

How to Mitigate CVE-2026-24290

Immediate Actions Required

• Apply the latest Windows security updates from Microsoft as soon as they become available
• Audit systems to identify where Windows Projected File System is enabled and in use
• Restrict local access to systems where ProjFS is critical, limiting potential attacker entry points
• Ensure endpoint protection solutions like SentinelOne are deployed and updated to detect exploitation attempts

Patch Information

Microsoft has released a security update addressing this vulnerability. Organizations should consult the Microsoft Security Response Center advisory for CVE-2026-24290 for specific patch details, affected product versions, and update guidance.

Apply the security update through Windows Update, Windows Server Update Services (WSUS), or Microsoft Update Catalog based on your organization's patch management infrastructure.

Workarounds

• If ProjFS is not required for business operations, consider disabling the Windows Projected File System feature via Optional Features
• Implement application whitelisting to prevent unauthorized executables from running on critical systems
• Apply the principle of least privilege to limit the number of accounts with local system access
• Use network segmentation to limit the impact of potential privilege escalation on compromised systems

# Check if Windows Projected File System is enabled (PowerShell)
Get-WindowsOptionalFeature -Online -FeatureName Client-ProjFS

# Disable Windows Projected File System if not required (PowerShell as Administrator)
Disable-WindowsOptionalFeature -Online -FeatureName Client-ProjFS -NoRestart