CVE-2026-20937: Windows File Explorer Info Disclosure Flaw

CVE-2026-20937 Overview

CVE-2026-20937 is an information disclosure vulnerability in Windows File Explorer that allows an authorized attacker to expose sensitive information through local access. This vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), indicating that the affected component improperly handles access to sensitive data, potentially allowing a lower-privileged user to access information they should not be authorized to view.

Critical Impact

Local attackers with valid credentials can exploit this vulnerability to disclose sensitive information through Windows File Explorer, potentially exposing confidential data, system configurations, or other protected resources.

Affected Products

• Windows File Explorer

Discovery Timeline

• January 13, 2026 - CVE-2026-20937 published to NVD
• January 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20937

Vulnerability Analysis

This vulnerability represents an information exposure flaw within Windows File Explorer, one of the most fundamental components of the Windows operating system. The weakness allows an authenticated attacker with local access to the system to disclose sensitive information that should otherwise be protected.

The vulnerability requires local access and low privileges to exploit, meaning an attacker must first gain access to the target system, either through a legitimate user account or through another initial access vector. Once access is obtained, the attacker can leverage the flaw in File Explorer to access protected information. The confidentiality impact is high, while integrity and availability remain unaffected, indicating this is purely an information disclosure issue.

Root Cause

The root cause of this vulnerability stems from improper access control mechanisms within Windows File Explorer (CWE-200). The component fails to adequately restrict access to sensitive information when processing file system operations, allowing users with standard privileges to potentially view data that should be restricted to higher-privileged accounts or system processes.

Attack Vector

This vulnerability requires local access to exploit. An attacker must first have authenticated access to the target Windows system with at least low-level privileges. The attack does not require user interaction beyond the attacker's own actions, making it straightforward to exploit once local access is established.

The exploitation scenario typically involves:

1. An attacker gaining local access to a Windows system through legitimate credentials or another compromise
2. Using Windows File Explorer to navigate or interact with specific file system locations
3. Exploiting the improper access controls to view sensitive information
4. Exfiltrating or using the disclosed information for further attacks

Since no verified proof-of-concept code is publicly available, the specific technical mechanism for exploitation has not been disclosed. For detailed technical information, refer to the Microsoft Security Update for CVE-2026-20937.

Detection Methods for CVE-2026-20937

Indicators of Compromise

• Unusual file access patterns in Windows File Explorer by low-privileged users accessing sensitive directories
• Unexpected reads of protected files or directories by standard user accounts
• Anomalous File Explorer process behavior including access to restricted system locations
• Evidence of sensitive data being copied or accessed through File Explorer operations

Detection Strategies

• Monitor Windows Security Event Logs for file access events (Event ID 4663) involving sensitive files or directories
• Implement file integrity monitoring on critical system and data directories
• Deploy endpoint detection solutions capable of monitoring File Explorer behavior and file system access patterns
• Audit user access patterns and flag anomalous access to sensitive resources by standard accounts

Monitoring Recommendations

• Enable detailed file system auditing through Windows Security Policy for sensitive directories
• Configure SentinelOne endpoint protection to monitor for suspicious File Explorer activity and information access patterns
• Review Windows Event Logs regularly for unauthorized file access attempts
• Implement data loss prevention (DLP) controls to detect potential data exfiltration following information disclosure

How to Mitigate CVE-2026-20937

Immediate Actions Required

• Apply the Microsoft security update for CVE-2026-20937 as soon as available
• Review and restrict local user access permissions to sensitive files and directories
• Implement the principle of least privilege for all user accounts
• Enable detailed auditing on sensitive file system locations to detect potential exploitation attempts

Patch Information

Microsoft has released a security update to address this vulnerability. System administrators should apply the official patch through Windows Update or WSUS (Windows Server Update Services). The security update details are available through the Microsoft Security Response Center.

Workarounds

• Restrict local access to systems containing sensitive information until the patch can be applied
• Review and tighten NTFS permissions on sensitive directories and files
• Implement additional access controls through Group Policy to limit File Explorer functionality for standard users
• Consider using third-party file managers with enhanced access control capabilities for accessing sensitive data

# Example: Audit sensitive directory access via PowerShell
# Enable auditing on a sensitive folder
$AuditRule = New-Object System.Security.AccessControl.FileSystemAuditRule("Everyone","Read","Success,Failure")
$Acl = Get-Acl "C:\SensitiveData"
$Acl.AddAuditRule($AuditRule)
Set-Acl "C:\SensitiveData" $Acl