CVE-2021-24084: Windows 10 MDM Information Disclosure

CVE-2021-24084 Overview

CVE-2021-24084 is an information disclosure vulnerability in the Windows Mobile Device Management (MDM) component that allows local attackers with low privileges to access sensitive information. This vulnerability stems from improper link following (CWE-59), which can be exploited to read arbitrary files on an affected system. The vulnerability affects various versions of Windows 10 and Windows Server platforms.

Critical Impact

A local attacker with low privileges can exploit this vulnerability to disclose sensitive information from the target system, potentially leading to further attacks or data breaches.

Affected Products

• Microsoft Windows 10 (versions 1803, 1809, 1909, 2004, 20H2)
• Microsoft Windows Server 2016 (versions 1909, 2004, 20H2)
• Microsoft Windows Server 2019

Discovery Timeline

• 2021-02-25 - CVE-2021-24084 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-24084

Vulnerability Analysis

This vulnerability exists in the Windows Mobile Device Management diagnostics functionality. The MDM component improperly handles symbolic links (symlinks), falling under CWE-59 (Improper Link Resolution Before File Access). When the MDM diagnostics process accesses certain resources, it fails to properly validate link targets, allowing an attacker to redirect file operations to arbitrary locations on the filesystem.

The attack requires local access to the target system and low-level privileges. Upon successful exploitation, an attacker can read sensitive files that should otherwise be restricted, leading to high confidentiality impact. The vulnerability does not directly allow code execution or system modification, focusing purely on information disclosure.

Root Cause

The root cause is improper link resolution before file access (CWE-59). The Windows MDM component follows symbolic links without adequate validation, allowing an attacker to create malicious symlinks that redirect file read operations to sensitive system files or user data that should not be accessible to low-privileged users.

Attack Vector

The attack requires local access to the target system. An attacker with low privileges must first gain local access, then create strategically placed symbolic links that the MDM diagnostics component will follow during its normal operations. When the MDM component processes these links, it inadvertently reads and potentially exposes the contents of files the attacker should not have access to.

The exploitation process involves:

1. Identifying the file paths used by the MDM diagnostics functionality
2. Creating symbolic links pointing from those paths to sensitive target files
3. Triggering the MDM diagnostics operation to read through the crafted symlinks
4. Capturing the disclosed information from the redirected file operations

Detection Methods for CVE-2021-24084

Indicators of Compromise

• Unusual symbolic link creation in MDM-related directories or paths
• Unexpected file access patterns from the MDM diagnostics service
• Low-privileged user accounts accessing sensitive system files through indirect means
• Audit log entries showing file reads that don't match normal MDM operational patterns

Detection Strategies

• Monitor for symbolic link creation events in directories associated with MDM diagnostics functionality
• Implement file integrity monitoring on sensitive system files that could be targets of information disclosure
• Use endpoint detection and response (EDR) solutions to track process behavior and file access patterns
• Enable Windows Security auditing for object access to detect anomalous file reads

Monitoring Recommendations

• Configure Windows Event Log auditing to capture symbolic link creation and file access events
• Deploy SentinelOne Singularity platform to monitor for suspicious file system operations and process behaviors
• Review MDM-related process activities for unexpected file access patterns
• Establish baselines for normal MDM component behavior to detect deviations

How to Mitigate CVE-2021-24084

Immediate Actions Required

• Apply the latest Windows security updates from Microsoft to patch the vulnerability
• Review and restrict local access privileges to reduce the attack surface
• Audit user accounts with local access to identify potential threat actors
• Implement the principle of least privilege for all user accounts

Patch Information

Microsoft has released security updates to address this vulnerability. Administrators should apply patches through Windows Update or download them directly from the Microsoft Security Advisory CVE-2021-24084. It is strongly recommended to test patches in a staging environment before deploying to production systems.

Workarounds

• Restrict local access to systems where MDM functionality is not required
• Disable unnecessary MDM diagnostic features if they are not being used in your environment
• Implement strict access controls on sensitive files and directories that could be targeted
• Monitor for and remove unauthorized symbolic links in system directories

# Verify patch status on Windows systems
wmic qfe list brief /format:table
# Check for specific security update related to CVE-2021-24084
wmic qfe get hotfixid | findstr /i "KB"