CVE-2021-31843: McAfee Endpoint Security Privilege Escalation

CVE-2021-31843 Overview

An improper privileges management vulnerability exists in McAfee Endpoint Security (ENS) for Windows prior to version 10.7.0 September 2021 Update. This security flaw allows local users to access files which they would otherwise not have access to by manipulating junction links to redirect McAfee folder operations to an unintended location. The vulnerability is classified under CWE-59 (Improper Link Resolution Before File Access), also known as a symlink attack or link following vulnerability.

Critical Impact

Local attackers can leverage this vulnerability to achieve unauthorized file access and potentially escalate privileges on affected Windows systems running vulnerable versions of McAfee Endpoint Security.

Affected Products

• McAfee Endpoint Security for Windows versions prior to 10.7.0 September 2021 Update
• McAfee Endpoint Security 10.7.0 with updates from February 2020 through June 2021
• McAfee Endpoint Security 10.7.0 including April 2020, July 2020, September 2020, and November 2020 releases

Discovery Timeline

• 2021-09-17 - CVE-2021-31843 published to NVD
• 2026-02-24 - Last updated in NVD database

Technical Details for CVE-2021-31843

Vulnerability Analysis

This vulnerability stems from improper handling of filesystem operations within McAfee Endpoint Security's privileged processes. When the security software performs file operations on specific directories, it fails to properly validate whether the target path has been manipulated through junction links (Windows symbolic links for directories).

An attacker with local access can exploit this by creating a junction point that redirects McAfee's folder operations from their intended target to arbitrary locations on the filesystem. Because McAfee ENS operates with elevated privileges (SYSTEM-level permissions), any file operations redirected through these junction links execute with the same elevated privileges, allowing unauthorized access to protected files and directories.

Root Cause

The root cause is CWE-59: Improper Link Resolution Before File Access. The McAfee ENS software does not adequately verify that file paths are genuine before performing privileged operations. Specifically, the application follows junction links without checking whether the resolved path matches the expected destination, enabling attackers to redirect operations to arbitrary filesystem locations through symbolic link manipulation.

Attack Vector

The attack requires local access to the target system. An attacker must:

1. Identify privileged folder operations performed by McAfee ENS
2. Create a junction link (directory symbolic link) at a location McAfee accesses
3. Point the junction link to a target directory the attacker wishes to access
4. Trigger the McAfee operation that follows the junction link
5. The privileged McAfee process will then perform file operations on the redirected target location

This symlink-based attack technique is a well-documented method for privilege escalation in Windows environments where high-privilege applications follow filesystem links without proper validation.

Detection Methods for CVE-2021-31843

Indicators of Compromise

• Unexpected junction links created in McAfee installation directories (typically C:\Program Files\McAfee\)
• Suspicious symbolic link creation events involving McAfee-related paths
• Unusual file access patterns from McAfee processes to unrelated system directories
• Local user accounts creating directory junctions in system-protected locations

Detection Strategies

• Monitor for junction link creation events using Windows Security Event logs or Sysmon
• Implement file integrity monitoring on McAfee installation directories
• Audit symbolic link creation operations by non-administrative users
• Use endpoint detection tools to identify suspicious process behavior from McAfee services accessing unusual paths

Monitoring Recommendations

• Enable detailed file system auditing on Windows endpoints running McAfee ENS
• Deploy SentinelOne's behavioral AI to detect anomalous file access patterns from security software processes
• Configure alerts for junction link creation in system directories
• Monitor for privilege escalation attempts following filesystem manipulation

How to Mitigate CVE-2021-31843

Immediate Actions Required

• Update McAfee Endpoint Security to version 10.7.0 September 2021 Update or later immediately
• Audit systems for unauthorized junction links in McAfee directories
• Restrict local user permissions where possible to minimize attack surface
• Enable enhanced logging to detect potential exploitation attempts

Patch Information

McAfee has addressed this vulnerability in the September 2021 Update for Endpoint Security version 10.7.0. Organizations should apply this update immediately through their standard McAfee deployment mechanisms. Detailed patch information is available in the McAfee Security Advisory SB10367.

Workarounds

• Restrict local user access to systems running vulnerable McAfee ENS versions until patching is complete
• Implement application whitelisting to prevent unauthorized symbolic link creation tools
• Deploy additional endpoint monitoring to detect junction link abuse attempts
• Consider using Windows security policies to restrict symbolic link creation for non-administrative users

# Check McAfee ENS version on Windows
# Run in Command Prompt as Administrator
wmic product where "name like 'McAfee Endpoint Security%'" get name,version

# List junction links in McAfee directories for audit
dir /AL "C:\Program Files\McAfee\" /S