CVE-2021-31840
📋 TL;DR
This vulnerability allows authenticated local attackers on Windows systems with McAfee Agent to perform DLL preloading attacks using unsigned DLLs, leading to privilege escalation and arbitrary code execution. It affects McAfee Agent for Windows versions prior to 5.7.3. Attackers need valid local credentials to exploit this vulnerability.
💻 Affected Systems
- McAfee Agent for Windows
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An authenticated attacker gains SYSTEM-level privileges and executes arbitrary code, potentially leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Malicious insiders or attackers with stolen credentials escalate privileges to install malware, maintain persistence, or move laterally within the network.
If Mitigated
With proper patch management and least privilege controls, impact is limited to isolated incidents that can be quickly contained.
🎯 Exploit Status
Requires local authentication and ability to place DLLs in specific directories. No public exploit code has been disclosed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.7.3 or later
Vendor Advisory: https://kc.mcafee.com/corporate/index?page=content&id=SB10362
Restart Required: Yes
Instructions:
1. Download McAfee Agent 5.7.3 or later from the McAfee support portal. 2. Run the installer with administrative privileges. 3. Restart the system as prompted. 4. Verify the update completed successfully.
🔧 Temporary Workarounds
Restrict DLL loading paths
windowsConfigure Windows to restrict DLL loading from untrusted directories using Group Policy or registry settings.
reg add "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager" /v CWDIllegalInDllSearch /t REG_DWORD /d 0x1 /f
🧯 If You Can't Patch
- Implement strict least privilege principles to limit which users have local login rights
- Monitor for suspicious DLL loading behavior using Windows Event Logs and EDR solutions
🔍 How to Verify
Check if Vulnerable:
Check McAfee Agent version via Control Panel > Programs and Features or using command: Get-WmiObject -Class Win32_Product | Where-Object {$_.Name -like "*McAfee Agent*"} | Select-Object Name, VersionCheck Version:
Get-WmiObject -Class Win32_Product | Where-Object {$_.Name -like "*McAfee Agent*"} | Select-Object VersionVerify Fix Applied:
Verify version is 5.7.3 or higher using the same command and check that no unsigned DLLs are being loaded from untrusted locations.📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing DLL loading from unusual locations
- McAfee Agent logs showing unexpected DLL loading behavior
Network Indicators:
- Unusual outbound connections from systems with McAfee Agent
SIEM Query:
EventID=7 AND (ImagePath="*\McAfee\*" OR ProcessName="*McAfee*") AND (FileName="*.dll")