CVE-2024-20671: Windows Defender Auth Bypass Vulnerability

CVE-2024-20671 Overview

CVE-2024-20671 is a security feature bypass vulnerability affecting Microsoft Windows Defender Antimalware Platform. This vulnerability allows a local attacker with low privileges to bypass security features in Microsoft Defender, potentially leading to a denial of service condition where the antimalware protection becomes unavailable.

Critical Impact

Successful exploitation allows attackers to disable or bypass Microsoft Defender security protections, leaving systems vulnerable to malware and other threats.

Affected Products

• Microsoft Windows Defender Antimalware Platform

Discovery Timeline

• 2024-03-12 - CVE-2024-20671 published to NVD
• 2024-11-29 - Last updated in NVD database

Technical Details for CVE-2024-20671

Vulnerability Analysis

This vulnerability stems from improper default permissions (CWE-276) within the Microsoft Windows Defender Antimalware Platform. The flaw allows an authenticated local attacker to bypass security features, resulting in the potential disruption of antimalware services. The attack requires local access to the system and low-privilege credentials, but does not require user interaction.

The vulnerability primarily impacts system availability rather than confidentiality or integrity. When successfully exploited, attackers can cause high availability impact by disabling or degrading Microsoft Defender's protective capabilities.

Root Cause

The root cause of CVE-2024-20671 is attributed to CWE-276: Incorrect Default Permissions. The Windows Defender Antimalware Platform contains improperly configured default permissions that allow lower-privileged users to manipulate security settings or components they should not have access to. This misconfiguration creates an avenue for attackers to interfere with the normal operation of the antimalware service.

Attack Vector

The attack vector is local, meaning an attacker must have existing access to the target system. The exploitation scenario involves an authenticated user with standard privileges leveraging the incorrect permissions to disable or bypass Windows Defender protections. This could be achieved by modifying critical configuration files, tampering with service components, or exploiting weaknesses in the permission structure that governs Defender operations.

Successful exploitation does not require user interaction and can be executed once the attacker has established local access through other means such as phishing, credential theft, or physical access to the machine.

Detection Methods for CVE-2024-20671

Indicators of Compromise

• Unexpected changes to Windows Defender service status or configuration
• Windows Defender real-time protection being disabled without administrative action
• Audit log entries showing permission modifications to Defender-related directories or files
• MpCmdRun.exe or Defender service exhibiting abnormal behavior or failures

Detection Strategies

• Monitor Windows Security Center events for unexpected Defender status changes
• Implement audit policies to track modifications to %ProgramFiles%\Windows Defender\ directories
• Configure alerts for Windows Defender service (WinDefend) stop or restart events
• Review Windows Event logs for Event ID 5001 (Real-time protection disabled) and related Defender events

Monitoring Recommendations

• Enable Windows Defender Antivirus event logging via Group Policy
• Configure SIEM rules to detect patterns of security feature manipulation
• Implement endpoint detection solutions like SentinelOne to monitor for Defender tampering attempts
• Regularly audit permission settings on Windows Defender installation directories

How to Mitigate CVE-2024-20671

Immediate Actions Required

• Apply the latest Microsoft security updates for Windows Defender Antimalware Platform immediately
• Verify Windows Defender is running and properly configured after patching
• Review and restrict local user permissions where possible to limit exposure
• Monitor for any signs of exploitation attempts on unpatched systems

Patch Information

Microsoft has released a security update to address CVE-2024-20671. The patch corrects the permission issues in the Windows Defender Antimalware Platform. Administrators should apply updates through Windows Update, Windows Server Update Services (WSUS), or Microsoft Update Catalog.

For detailed patch information and download links, refer to the Microsoft Security Update Guide for CVE-2024-20671.

Windows Defender Antimalware Platform typically updates automatically through Windows Update. Verify that automatic updates are enabled and that the platform version has been updated to the patched version.

Workarounds

• Ensure only administrators have write access to Windows Defender directories and registry keys
• Implement application control policies to prevent unauthorized modifications to Defender components
• Use Microsoft Defender for Endpoint or third-party endpoint protection like SentinelOne as an additional security layer
• Monitor and alert on any attempts to stop or disable the Windows Defender service

# Verify Windows Defender service status
sc query WinDefend

# Check current Defender platform version
powershell -Command "Get-MpComputerStatus | Select-Object AMProductVersion, AMServiceVersion"

# Ensure real-time protection is enabled
powershell -Command "Set-MpPreference -DisableRealtimeMonitoring $false"